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Diseases and Insects. Under one head it is thought best to bring together the discussions of the so-called enemies of plants, — the parasitic fungi and the depredating insects, together with the means of control. This composite article therefore comprises:
Diseases due to parasitic fungi .................... 1021
Fungicides, or remedies for these diseases .......... 1027
Catalogue of diseases, with advice ................. 1029
Insects and their depredations on plants ........... 1034
Insecticides and fumigation ...................... 1042
Catalogue of insect depredators, with advice ....... 1047
Spraying ....................................... 1057

The reader now has before him a comprehensive survey of the subject. It is impossible, of course, to list all the plant diseases and all the insect pests in a compilation of this kind; but it is desired that the catalogues shall comprise the most important depredators of the leading horticultural plants. The reader should keep himself informed of the new knowledge and new practice by consulting current publications of the government and the experiment stations.

Diseases of plants.

Disease in plants may be defined as any derangement or disorganization of the normal structure or physiological functions of the plant, as for example the formation of (jails, cankers or distortions, rotting of plant parts, or disturbances in the sap system resulting in wilting, or in the nutritive processes resulting in such symptoms as dwarfing, chlorosis, and the like. Forms of plant diseases are shown in Figs. 1279-1292.

It is often very difficult to distinguish clearly between diseased conditions and abnormalities of other types. Bud-sports, doubling of blossoms, fasciations and many other similar abnormalities, while often the result of reaction to some pathogen, are not apparently always so and they are often spoken of as teratological phenomena. While the reaction of plants to insect attacks in the formation of galls, cankers, and so on, is to be regarded as symptom of disease, the injuries produced by the mere eating away of parts of leaf, stem or fruit are not usually so to be regarded. Even here, however, it is often difficult to draw a sharp line of demarkation. While disease may usually be said to result in ultimate injury, there are apparently certain marked exceptions, as in the case of the root tubercles of legumes caused by the attacks of certain nitrogen-fixing parasitic bacteria. Here increased growth and crop-yield are generally held to result.

Diseases of plants are not something new or of recent development, as the grower is often inclined to think. The crops of the husbandman, from the earliest recorded history of his art, have been afflicted with diseases. In the historical writings of the Hebrews, the Bible, and in the writings of the Greeks and Romans, frequent mention is made of such diseases as rusts, smuts and mildews of grain and canker of trees. To be sure, the extensive and intensive crop-cultivation of modern times, together with the extraordinary worldwide transportation and exchange of crop-products, have greatly favored the distribution of plant pathogens (insects, fungi and bacteria), and afford them exceptional opportunities for destructive development. Nor are cultivated plants alone subject to disease. Disease epidemics among weeds and the wild flowers of the woods may be observed any season in localities in which weather conditions especially favor the causal organisms.

The study of the nature and control of plant diseases, however, is of recent development. The first man really to study plant diseases from the true modern economic point of view, that is, with the object of helping the grower to understand and combat or control diseases in his crops, was Julius Kuhn. This German, the son of a German land-owner and for many years himself the manager of a large agricultural estate, was the founder of an early German agricultural college. He interested himself, among other phases of agriculture, in plant diseases and their control and his book, "Die Krankheit der Kulturgewachse," published in 1858, is to be regarded as the first book of real economic importance on the subject of diseases in plants. In this remarkable volume is given a concise statement of the thoroughly digested and personally tested knowledge of his time, on the nature and control of plant diseases. He also describes a number of new methods, especially for seed treatment of cereals against smuts, which have become the foundation for many of our present-day practices.

Since Kuhn's day there have been remarkable developments in the control of plant diseases. The discovery of bordeaux mixture by the Frenchman Millardet in 1882; the discovery of the formaldehyde treatment of seed for smut by the American plant pathologist, Arthur, in 1896; and the recent development of the use of lime-sulfur solutions and mixtures as a substitute for bordeaux in the spraying of apples and peaches, are but the most noteworthy of the many discoveries and developments in the remarkable growth of this economic science within the last half century.

The economic importance of plant diseases can scarcely be overestimated, as they constitute one of the chief losses in our agricultural resources. The loss from 5 to 25 per cent of many crops from diseases alone each year is so common as to be the general rule. The loss from potato diseases each season in the United States has been carefully estimated at not less than $36,000,000. Yet, it has been conclusively demonstrated by extensive experiments among potato-growers during a continuous period of ten years, that an annual average increase of over forty bushels per acre may be expected from spraying the crop with bordeaux mixture, from three to five times in the season at a total average cost of about $5 per acre. The loss from oat- smut commonly averages from 5 to 25 per cent of the crop, yet it may be absolutely prevented by seed treatment at almost insignificant cost. The loss from scab in the apple crop of New York State often totals not less than $3,000,000 and for the United States a corresponding loss of over $40,000,000. In 1900, the peach-growers of Georgia lost $5,000,000 by brown rot, while the average annual loss from the same disease in the entire United States is never less. Yet in each case here mentioned, as well as in most of the other of our common and destructive diseases, cheap and effective means of control are within the reach of every grower. The value and efficiency of these means have been established beyond doubt. Their profitable application requires only intelligence and practice on the part of the grower.

Symptoms of disease in plants are so varied in character as to make an attempt at wholly satisfactory grouping for practical purposes of doubtful value. Mention of some of the more common types, however, may be useful. The grower must learn by study and experience the more sinking symptoms characteristic of t hose diseases peculiar to the crops that he grows.

Disease may be exhibited in malformations of the leaf, stem, root or fruit, as for example, knots, gulls, tubercles, curling, wrinkling or other distortions. There are such symptoms in crown-gall of trees, black-knot of plums and cherries and leaf-curl of the peach (Fig. 1279). Another type are cankers, dead sunken or roughened areas in the bark of trees or the outer rind of herbaceous stems, as for example in the New York apple- tree canker, the brown- rot canker of peaches, frost cankers of many trees, and anthracnose of beans, melons, and others. The blight type of lesion is also very common. Here are the more or less sudden death of leaves, stems, shoots or blossoms, usually turning dark and drying up. Such symptoms characterize fire-blight of fruit trees, potato- blight (Fig. 1280, from Vt. Sta.), alternaria blight of ginseng and similar diseases, especially in their last stages. The leaf- or fruit-spot type is also very common. Brown or black spots appear in foliage or fruit. They may be brown dead or rotted areas, or spots due to the growth of the parasite on or under the surface. Bordeaux-injury spots on apple foliage, shot-hole leaf injury of stone fruits, leaf- spot of the currant (Fig. 1281), celery or alfalfa, the tar-spot of the maple, the black-spot of the rose and the apple-scab are of this type. Another not uncommon type is that exhibited in certain bacterial and fungous diseases, where the pathogen infests the sap- tube regions of the stems or petioles, resulting in a sudden wilting of leaves and shoots. The wilt diseases of cotton, cucumber, ginseng, watermelon and cowpeas are characterized by this symptom. The yellowing of the foliage, either suffused or localized as spots, rings, and blotches and often accompanied by dwarfing and wrinkling of the affected organs is a common symptom of certain so-called physiological diseases like the peach yellows (Figs. 1282, 1283), little-peach, mosaic disease of tobacco, infectious chlorosis and nitrogen-poisoning of greenhouse cucumbers (Fig. 1284) and other plants.

The causes of disease in plants.

Etiology, or the cause of disease, has been more generally and carefully investigated than any other phase of the subject, so that we now know much regarding the agents primarily responsible for most plant diseases. These agents may be grouped as follows: Slime molds, lowly organisms having characters of both plants and animals (see article Fungi). The club- root of cabbage, cauliflower and other crucifers, is the best known slime-mold disease.

Bacteria, microscopic unicellular plants which multiply very rapidly by simple fusion (see article Fungi). While most species are harmless scavengers of dead organic matter, and a few are known to cause diseases of men and animals, not less than 150 different diseases of plants are now known to be due to the attacks of parasitic bacteria. Some of the commonest bacterial diseases of plants are, fire-blight, crown-gall, olive-knot, soft-rot of vegetables, potato-scab, cucumber-wilt and black-leg of potatoes. Fungi (see Vol. Ill) are perhaps responsible for far the greater number of the diseases of plants. They are the causal agents in such well-known diseases as apple- scab, brown-rot of plums and peaches (Fig. 1285), black-rot of grapes, (Fig. 1286) bitter-rot of apples, brown-rot of lemons, late blight of potatoes, peach leaf-curl, heart-rot and canker of trees, mildew of many plants, rusts and smuts of cereals (Figs. 1287, 1288, Kansas Experiment Station); in fact the mere enumeration of the more common fungous diseases of plants would fill many columns in this volume.

Algae, low forms of green plants, most of them living in water or very damp places. Few are known to produce disease in plants. The red rust of tea is one of the best known algal diseases.
Parasitic angiosperms,—flowering plants, of which there is no inconsiderable number, causing more or less injury to the plants upon which they live. These parasites are usually markedly degenerate in one or more respects, as a result of their parasitism, being often without true roots, or without leaves and frequently without chlorophyl green. As examples we may mention the mistletoes, dodders and broom rapes.

Insects (see page 1034) cause such diseases as galls and similar malformations.

Nematode worms.—minute all but microscopic in size and multiplying rapidly, they constitute one of the greatest crop pests, especially in warm or tropical countries. They usually infest the roots, causing galls or swellings. Some species injure the plants by destroying the fine feeding roots as in the case of the nematode parasites of oats so destructive in certain countries of northern Europe. Over 400 different plants are known to be subject to the nematode root-gall disease. (See pp. 1041-2.)

Physiological disease is a term under which is included all those diseases the cause of which cannot be attributed to some parasitic organism. Their origin is variously attributed to abnormal enzymic activity, disturbed nutrition, and the like. The best-known of these are peach-yellows, chlorosis of the vine, tip-burn (Fig. 1291), mosaic disease of tobacco and leaf-roll disease of potatoes.

The various parasitic organisms cause disease in one of two ways, either by the secretion of toxines and enzymes which at once kill the plant tissues and change them into forms readily available as food for the invader; or the toxins and enzymes secreted merely stimulate or irritate the plant tissues in such a way as to result in abnormal tissue growth or diversion of the food substances of the host to the advantage of the parasite making its home between or in the cells of the host. Both types of disease-production have the same ultimate result, the serious injury or destruction of the infested plant, although the former is usually the more rapid and destructive.
Of the first type, rots, blights and leaf-spots are the best examples, and are characterized by the rapid death and destruction of the affected tissues; of the second type, galls, leaf- curls, rusts and smuts are good examples and are characterized by a rather long period of association of the parasite with the living tissues of its host before marked injury or death of the plant results.

The causal agent is usually associated with the tissues of the host, either the dead or living, during its entire cycle of development. The apple-scab pathogen, Venturia inaequalis, will serve admirably to illustrate. It passes the summer on the surface of leaf and fruit. In the autumn when the infested leaves fall to the ground, the fungus, which as a parasite has invaded only the cuticle of the leaf or fruit, now penetrates the dead tissues and develops there during the autumn the winter form of fruit bodies, the minute globose black perithecia, in which during the warm days of early spring the ascospores are rapidly developed. These ascospores (Fig. 1292), eight in a sac, ripen and are discharged by the spring rains that come during the blossoming period. The old leaves on the ground are filled with millions of these minute perithecia with many sacs of ascospores in each perithecium. The spores are shot into the air during the rain and being exceedingly light are carried to the opening leaves and forming fruits, where they germinate, sending out mycelial threads into the cuticle of leaf or fruit forming the characteristic dense dark green or black mats or crusts, the scab-spots. The leaves become crumpled and injured, the young fruits grow one-sided, or if the stem be attacked, soon drop from the tree, thus giving no set of fruit. On the scab-spots the conidia or summer spores cut off from the tips of upright branches in great numbers, are carried by the wind to other leaves and fruits where, with the next rain, they germinate and give rise to new scab-spots and more conidia.

The life-cycle as given for the apple-scab fungus is typical of many of the fungous pathogens of our crops. It must be remembered, however, that each pathogen has habits peculiar to itself; hence the necessity for the most careful study of each that we may know its habits and peculiarities and thus be able successfully to combat it. The following illustrations will serve to explain and impress this point.

Plowrightia marbosa, the fungus causing black-knot of plums and cherries, requires two seasons to complete its life-cycle. The first season there appears on the knots only conidia, followed the second season by a crop of ascospores, produced in perithecia, which form a black crust on the surface where the conidia were earlier produced. Other pathogens like Exoascus cerasi, the "witches broom pathogen of the cherry, lives from year to year as mycelium in the branch and twigs of the broom-like growths it excites, producing each season a crop of spores on the under sides of the leaves. The blister-rust fungus of the white pine, Cronartium ribicolum, also lives from season to season in the tissues of the pine, producing each spring a new crop of spores. This pathogen exhibits another habit peculiar chiefly to certain of the rust fungi, namely that it has another stage or spore form on an entirely different host plant, in this case, the currant, especially the European black currant. The apple-rust pathogen, Gymnosporangium macropus, exhibits the same habit, passing the winter in galls formed on the twigs of the red cedar. In the spring spores appear on these galls, which germinating in situ give rise to other minute spore bodies, the sporidia. These sporidia are carried by the wind to the young apple leaves and fruit, giving rise there to the rust disease so destructive to certain varieties like the Mclntosh and York Imperial. The spores formed on the rusted leaves and fruit of the apple are carried to the cedar, originating a new crop of galls and thus completing the life-cycle.

While some pathogens may develop in both living and dead tissues of their host, as we have seen in the case of the apple-scab fungus, other pathogens like the rust organism just described or the potato-blight pathogen, Phytophthora infestans, require to be constantly associated with the living tissues of their host The last-mentioned fungus passes the winter as mycelium in the tissues of diseased tubers, grows from thence up through the new shoots, slowly killing them and forming thereon the first crop of conidia, which, carried by the wind to nearby healthy plants, produce the primary infections of the season. The successive crops of conidia produced during the season on the blighted tops are washed into the soil by the rains, find their way to the newly formed tubers, and, infecting them, complete the seasonal cycle of the parasite.

Many fungous pathogens are now known to pass from one generation of the host plant to the next through the seed. The smut parasites of cereals afford remarkable examples of this habit. In the case of the oat- smut fungus, Ustilago avenae, the spores ripen as dusty black masses in the panicles of affected plants just as the healthy plants are in blossom. At this time the two hulls inclosing the grain are open. The wind-scattered spores lodge in the open flowers against the young kernel where they are soon safely housed by the closing hulls. They lie dormant along with the ripened seeds until they are planted. Then as the oat kernels germinate, the smut spores do likewise, sending forth their germ tubes which penetrate the young oat sprouts before they emerge from the hull. The mycelium grows along up through the growing oat straw, finally giving rise to the black spore masses in the unfolding panicle. In the case of stinking smut of wheat the seasonal life- cycle of the pathogen, Tilletia tritici, is much the same, except that the spores are disseminated at threshing time. Some very important differences in the habits of the loose smut pathogens of wheat, Ustilago tritici and of barley, Ustilago nuda, have recently been discovered (1902). The spores of these pathogens are also ripened and disseminated at blossoming time, but on falling within the open blossom they germinate at once, sending their germ-tubes into the tender young kernels. The affected kernels are apparently not injured but continue to develop and ripen. The mycelium of the pathogen within remains dormant until the seeds are planted and begin to grow, at which time the mycelium also becomes active. It grows out into the young shoots and up through the lengthening culms eventually to give rise to the black spore masses of the smutted heads. The bean anthracnose fungus, Colletotrichum lindemuthianum, is also carried over in the seed. Here the fungus in the black spots or cankers on the pods penetrates into the tender cotyledons of the seed within, goes into a dormant condition as the seed ripens, to become active again when the germinating seed lifts these cotyledons from the soil. A new crop of spores is produced, which, if the season be rainy, are splattered on to the stems and leaves of nearby healthy plants and the pathogen becomes established for another season.

While the wind is the most common disseminating agent of fungus spores, often carrying them for great distances, such agents as rain, flowing water, insects and even man himself, are frequently responsible. It is in the dissemination of bacterial pathogens, however, that insects most generally function. The dreaded fire-blight bacteria are disseminated only by insects or man. They pass the winter in a semi-active state in the half-living tissues along the margins of cankers on limbs or twigs, multiply rapidly with the rise of sap and the heat of spring. They ooze from the affected bark in sticky, milky drops. This ooze is visited by bees and flies, which with besmeared legs and mouthparts fly away to visit the opening apple or pear blossoms. Here they leave some of the bacteria in the nectar where they rapidly multiply, to be more widely distributed by each succeeding visitor. They soon penetrate into the tender tissues of the blossom, causing the blossom blight. From these blighted blossoms, sucking insects like the aphids carry the bacteria to the tips of the rapidly growing shoots when in sucking sap they introduce the organisms and twig blight follows. The striped cucumber beetle is probably the chief disseminator of Bacillus tracheiphilus, which causes the cucumber-wilt.

Ecological conditions as affecting disease.

By ecology is meant the influence of such environmental factors as climate, weather, soil and fertilizers, on the disease, its severity, epidemic occurrence, and the like. These factors may influence the severity of the disease by their effect on either the pathogen or the host, or both. For example, most fungous parasites require the presence of water on the host plant in which their spores may germinate, hence severe epidemics of such' diseases as potato-blight, apple-scab, brown-rot of stone fruits and black-rot of grapes usually appear in wet seasons. Moreover, the attacking pathogen is especially favored by wet weather at certain seasons or periods in its development, especially the infection period. Continued spring rains about blossoming time favor apple-scab and peach leaf-curl. Late summer rains bring with them epidemics of late blight of potatoes, brown-rot of peaches or late infections of apple-scab. Frequent or continuous rains during June and July in grape regions are usually accompanied by severe attacks of the black-rot pathogen. The relation of rainfall to the pathogen explains why, when there has been a severe epidemic the previous season, the crop may escape if the following season be dry. There is ever a critical period in the development of the pathogen, usually when it is passing from its resting or winter stage to the active vegetative period of the growing season. Moisture and temperature conditions at such periods largely determine whether the disease will be epidemic or not. Of course the necessary abundance of spores to be disseminated is an evident necessity. Favorable weather alone cannot bring on disease as the grower too often believes.

The absence of rains at certain stages in their development is for other pathogens equally essential. The loose smuts of cereals afford good examples. Their spores are powdery and wind-borne and if rains fall when they are being disseminated, they are washed to the ground and perish instead of finding their way into the open blossoms of their host. Thus, clear sunny weather during the blossoming period of wheat and oats one season usually means a more or less severe epidemic of smuts the next, while rains at this time, even though there be an abundance of the disease, may mean a clean crop the following year.

On the other hand, weather conditions may determine the severity or absence of certain diseases by its effect on the host. Long-continued cold rainy weather in the spring, especially following a warm spell, results in a slow succulent growth of the developing peach leaves, rendering them especially susceptible to the attacks of the leaf-curl pathogen.

The application of certain fertilizers to the soil is known to have a direct effect, either favorable or unfavorable, on different pathogens.

The application of lime or of manure to the soil tends greatly to increase the scab of potatoes planted thereon; while, on the other hand, liming the soil prevents infection of cabbage and cauliflower by the club-root pathogen. Lime likewise favors the development of the root-rot of tobacco and ginseng caused by Thielavia basicola, while applications of acid phosphate tend to prevent infection by this pathogen. The effect of fertilizers on the susceptibility of the host has also been shown to be marked in certain cases. Barley, when fertilized with nitrogenous manures, becomes very susceptible to attacks of the mildew Erysiphe graminis. Certain varieties of wheat have been observed in Denmark to suffer severely from attacks of the rust Puccinia glumarum only when nitrogenous manures are applied. Excessive applications of barnyard manure to greenhouse cucumbers often cause a physiological disease, the symptoms of which are a curling, and dying of the margins of the leaves, accompanied by marked chlorosis or yellowing. Fertilizers or late continued cultivation of pear trees, by lengthening the period of active twig-growth, favor fire-blight, the bacteria of which infect only tender actively growing tissues.

Control of diseases.

By the term control is meant the profitable reduction of the losses ordinarily sustained from a given disease. The absolute prevention of many plant diseases is either impossible or unprofitable.

There are four fundamental principles upon which all methods of plant-disease control are based, viz.: (1) exclusion, (2) eradication, (3) protection and (4) immunization. Upon the first two are based those measures which are directed primarily against the pathogen, upon the last two those which are directed merely toward the protection of the host from pathogens commonly present in the environment. The order in which these principles are here presented represent the logical, though unfortunately not the historical or usual order of their development and application. We will consider briefly under each some of the more important methods now employed for the control of plant diseases.

1. Exclusion measures are directed toward keeping disease organisms, usually insects, fungi and bacteria, out of areas, regions or countries in which they do not occur. This is commonly attempted by the passing of laws forbidding the importation of plants affected with such parasites. As means of enforcing such regulations, some sort of inspection, either at port of entry or at point of destination, is provided. Inspection in the country from which they are exported is also often required. Absolute quarantine against all importation of certain plants from those countries in which dangerous diseases are known to occur is also being practised in some countries, as for example, prohibiting the importation of potatoes into the United States from those countries in which the black-scab is now known to occur. Exclusion measures, often undertaken when it is too late, are at best under present conditions of doubtful efficiency. Those interested in these methods of control should consult the various pest and disease acts of the different countries of the world. See Inspection, in Vol. III.

2. Eradication.—On the principle of eradication are based those measures which are directed to the elimination of pathogens already established. While absolute eradication is seldom to be effected, the pathogen may often be eliminated to such an extent as to reduce losses therefrom to a profitable minimum. In Denmark, the destruction of all barberry bushes, the alternate host of the grain-rust fungus, Puccinia graminis, has decidedly reduced the severity of this disease in recent years. The careful eradication of all diseased plants is often quite effective even in a small area, like a raspberry or blackberry plantation suffering from the red rust. Here the mycelium of the pathogen lives from year to year in the roots of diseased plants, which each spring send up diseased shoots. On the under side of the leaves of these shoots, the orange-red spores are produced in great abundance, and serve to spread the pathogen to healthy plants. As diseased plants are readily detected in early spring by the pale clustered shoots, they may be removed before spores appear and the pathogen thus eradicated. The black-knot of plums and cherries is most readily and profitably controlled in a similar manner, the knot-affected limbs and twigs being cut out and burned early in the spring before spores appear. The fire-blight of pears is to be controlled only by systematic eradication, first of all cankers in autumn or early spring, then of all blossom blight as fast as it appears and later of the affected twigs when twig-blight comes on. To be effective, the trees must be inspected two or three times each week throughout the growing season and all diseased parts removed at once as soon as discovered.

Another method of eradication especially applicable to seeds, tubers or bulbs, on which spores of the pathogen pass the dormant period, is disinfection. This is accomplished by the application of chemical poisons, either in solution, as powder or as gas, at a strength and for a period of time sufficient to destroy the pathogen without injury to the host. When the pathogen lives over as mycelium in the seed or tuber, the application of heat is sometimes effective. Formaldehyde, as a gas or in solution in water, is now generally employed for the eradication of the smut of oats, the stinking smut of wheat and the potato-scab. (For details of method, see Formaldehyde, p. 1028). The spraying of peach trees with copper-sulfate solution, lime-sulfur solution or bordeaux, just before the buds start in the spring, disinfects the trees by destroying the spores of the leaf- curl fungus which pass the winter on the buds.

Pathogens which attack the underground parts of plants may sometimes be eradicated by disinfection of the soil before planting. Drenching the soil with a formaldehyde solution of a strength sufficient to distribute one gallon of the strong 40 per cent solution to each 100 square feet of surface, wetting the soil to a depth of 6 to 8 inches, has been found to be very effective against damping-off, root-rot and similar diseases in forest tree seed-beds, ginseng seed-beds and in the benches in greenhouses. It is also often effective in the eradication of nematodes in greenhouses. Steaming of the soil is also very effective, destroying insects and weed seeds as well as pathogenic fungi. It is not always conveniently applied.

3. Protection measures are to be employed in those regions in which the pathogen is very generally and very thoroughly established, or in which for one reason or another eradication is impossible or unprofitable. They aim to protect the crop against attacks of the parasite by means of some external barrier. Spraying is the most commonly employed protective measure. In spraying, the susceptible surfaces of the plant are coated with some slowly soluble poison, known as a fungicide. Fungicides are of various types. They are applied in suspension in water, in solution or dry, i.e., in the form of a fine impalpable powder. The fungicide most generally applied in liquid spraying is bordeaux, a colloidal compound formed by the union of lime-milk and copper-sulfate solution. Minute blue gelatinous membranes are formed which remain for a time suspended in the liquid. When sprayed upon the plants the water soon evaporates, leaving a coating of these dried membranes. The active fungicidal principal in these bordeaux membranes is the copper. When leaves or fruit are rewetted by rains enough of the copper in these membranes comes into solution to prevent the germination of the spores of the parasite that may have been deposited thereon. (See under Bordeaux, p. 1028.)

Bordeaux, however, is sometimes injurious to such plants as peaches, plums and apples, and has, within the last few years, been largely replaced as a summer spray, especially for apples. Lime-sulfur, unlike bordeaux, is a solution. It is made by boiling together in water, lime and sulfur. A concentrated solution of certain poly-sulfides of calcium, chiefly penta- and tetra- sulfide, is thus obtained which, when properly diluted is applied in the same way as the bordeaux. (For method of preparation, see Lime-sulfur, p. 1028). When this solution dries on the leaves and fruit, it is rapidly converted by the action of the atmosphere into other calcium compounds and free sulfur. The sulfur is in a very finely divided state and is the active principal of lime-sulfur. It becomes oxidized in the presence of moisture probably as sulfuric or sulfurous acid, which prevents the germination of the spores of the pathogen. Flowers of sulfur and sulfur-flour, when very finely ground and applied dry by dusting or sprayed on in suspension in water, alone or with lime-milk (the so- called self-boiled lime-sulfur) are also quite effective against certain diseases. Dusting with sulfur is employed in combating powdery mildews of grapes, hops, roses and the rust of asparagus.

Lime-sulfur may not be used on potatoes and grapes, as it dwarfs the plants and reduces the yield, while bordeaux has just the opposite effect on these crops. Bordeaux, as already pointed out, is, however, injurious to leaves and fruit of the apple and to the foliage of peaches and certain varieties of plums. It will thus be seen that there is no universal fungicide and also that both the effect on the host and on the parasite must be considered. It is now known for example that while lime-sulfur is very effective against the apple-scab fungus, it has little fungicidal effect on the spores of the bitter-rot pathogen.

To be effective, fungicides must be applied before the disease appears. As the spores of most parasitic fungi germinate during the period of rainy cloudy weather, the fungicide, to be effective, must be applied before and not after such periods. They must not only be thoroughly applied to the susceptible parts but also at the proper stage of growth or development of the plant. To illustrate: the only effective periods for spraying apple trees for scab are: just before the blossoms open (not dormant); just after the petals fall; ten days or two weeks later; and again in late summer just before the late summer rains, to protect the rapidly developing fruit from late infection.

4. Immunization consists in establishing within the plant itself some condition which renders it immune or resistant to the attacks of the pathogens. Immune crops may be developed by selection and propagation of individuals naturally immune, whose immunity has been evidenced by their coming through an epidemic unscathed. Immune varieties may be crossed with susceptible ones having other especially desirable qualities and then by segregation and propagation strains of the crop may be developed combining the resistance or immunity of the one parent with the desirable qualities of the other. Some striking results have been obtained in this line of disease control as witness the wilt- resistant cotton, cowpeas and watermelon, the nematode-free Iron cowpea, rust-resistant wheat, barley, and asparagus, and the anthrac- nose-resistant clover. Nevertheless, this method of control, while the most ideal, is beset with many difficulties and uncertainties. That pathogens, as well as crops, vary, giving strains capable of attacking host plants immune to other strains of the same pathogen, has generally been overlooked by breeders, and doubtless accounts for the frequent failure of supposedly resistant varieties when transferred to new localities. The production of artificial immunity by the injection of some substance into the plant or by the application of certain substances (fertilizers, etc.) to the soil is at most only in the preliminary stages of experimentation and as yet offers but little of practical value to the grower. H. H. Whetzel.

Fungicides.

A fungicide is any material or substance that kills fungi or their spores. The word is used particularly for those substances employed in the warfare against parasitic fungi.
A satisfactory fungicide must be one that does not injure the plants and at the same time is effective against the parasite. For spraying, additional requirements are imposed: it should not dissolve readily in rain-water; it should adhere to foliage and fruit; in some cases it should be colorless in order not to make ornamentals more unsightly than when diseased. The fungicide which has been used most for general purposes is bordeaux mixture. Lately some other preparations, particularly lime-sulfur combinations, have come into use, and in many cases are supplanting bordeaux. There are in addition a large number of other substances which have fungicidal value and are in more limited use for specific cases. The following directions are taken, with modifications, from the author's part in Bailey's "Farm and Garden Rule-Book."

Practices.

Destroying affected parts. —It is important that all affected parts should be removed and burned, if possible. In the fall all leaves and fruit that have been attacked by fungi should be raked up and burned. Diseased branches should be severed at some distance below the lowest visible point of attack. Fungous disease a often spread rapidly, and prompt action is usually necessary. Practise clean and tidy culture.

Rotation of crops.—This is one of the most effective and practical means of heading off fungous diseases. It is especially applicable to diseases of roots or root- crops, but also to many other diseases of annual plants.

Sterilizing by steam.— This is an effective fungicidal practice for several soil - inhabiting organisms which attack roots and stems. This includes nematode worms. It is especially applicable in the greenhouse, where it may be applied (a) through sub-irrigation tile or through specially laid perforated steam pipes in the bottom of the bed. Cover the beds with blankets, introduce steam under pressure of forty to eighty pounds for two hours. Insert thermometers at various places to see that the soil is being uniformly heated. (6) A large galvanized iron tight box may be constructed with finely perforated trays 4 to 0 inches in depth. Soil placed in these trays and steamed for two hours as above will be freed from parasitic organisms. In this case the frames should be sprayed with a solution of formaldehyde, one pint in twelve gallons of water. Steam sterilization of soil may be used on intensively cultivated areas or extensive seed-beds. A portable boiler is necessary. The beds are sterilized after they have been prepared for seed, and just before the seed is sown. A galvanized pan of convenient dimensions and 6 to 8 inches deep is inverted, and the edges are pushed down into the soil 1 or 2 inches. The pan is connected with the steam boiler by means of a steam hose and live steam is run into the pan from twenty to forty minutes under a pressure of eighty pounds and up. The higher the pressure the deeper the soil will be sterilized. The pan must be weighted. Paths should be disinfected by spraying with copper sulfate one pound to fifty gallons of water or with formaldehyde solution one pint to twelve gallons of water. The cost of sterilizing is approximately three-fourths of a cent the square foot. It should be noted that soil-sterilization has an invigorating effect on many plants, and it will be necessary to run greenhouses at a lower temperature (5° to 10°) both night and day. Field-sterilization also kills weed seeds, and with the reduction of the cost of weeding makes the process practicable.

Substances.

Bordeaux mixture.—A bluish green copper compound that settles out when freshly slaked time and a solution of copper sulfate (blue-stone) are mixed. Many formulas have been recommended and used. The 5-5-50 formula may be regarded as standard. In such a formula the first figure refers to the number of pounds of copper sulfate, the second to the stone or hydrated time, and the third to the number of gallons of water. Bordeaux must often be used as weak as 2-2-50, on account of injury to some plants.

To make fifty gallons of bordeaux mixture, proceed as follows:

(1) Pulverize five pounds of copper sulfate (blue vitriol), place in a glass, wooden, or brass vessel, and add two or three gallons of hot water. In another vessel slake five pounds of quicklime in a small amount of water. When the copper sulfate is all dissolved, pour into a barrel and add water to make forty or forty-five gallons. Now strain the lime into this, using a sieve fifty meshes to the inch or a piece of cheese-cloth supported by ordinary screening. Stir thoroughly, and add water to the fifty-gallon mark. The flocculent substance which settles is the effective fungicide. Always stir vigorously before filling the sprayer. Never add the strong time to strong vitriol. Always add a large amount of water to one or the other first. Blue vitriol used alone would not only wash off quickly in a rain, but cause a severe burning of fruit and foliage. Lime is added to neutralize this burning effect of the copper. If the lime were absolutely pure, only slightly more than one pound would be required to neutralize this burning effect. For many purposes an excess of lime is not objectionable and may be desirable.
For nearly ripe fruit and ornamentals an excess of lime augments spotting. In such cases the least amount of lime possible should be used. Determine this by applying the cyanide test (2).

(2) Secure from the druggist 10 cents' worth of potassium ferrocyanide (yellow prussiate of potash) and dissolve it in water in an eight-ounce bottle. Cut a V-shaped slit in one side of the cork, Bo that a few drops of the liquid can be obtained. Now proceed as before. Add lime with constant stirring until a drop of the ferrocyanide ceases to give a reddish-brown color.

(3) When bordeaux mixture is desired in large quantities, stock solutions should be made. Place one hundred pounds of copper sulfate in a bag of coffee-sacking, and suspend in the top of a fifty- gallon barrel, and add water to the fifty-gallon mark. In twelve to fifteen hours the vitriol will be dissolved and each gallon of solution will contain two pounds of copper gulf ate. Slake a barrel of lime, and store in a tight barrel, keeping it covered with water. Lime so treated will keep all summer. It is really hydrated lime. This is often dried, pulverized, and offered on the market in paper bags of forty pounds each, under such names as ground time, prepared time, hydrated lime, and the like. If the paper u not broken, the time does not air-slake for a long time. One and one-third pounds of hydrated time equals in value one pound of quicklime. Air-slaked time cannot be used in preparing bordeaux mixture.

Arsenical poisons can be combined with bordeaux mixture.

Ammoniacal copper carbonate.—For use on nearly mature fruit and on ornamentals. Does not discolor. Weigh out three ounces of copper carbonate, and make a thick paste with water in a wooden pail. Measure five pints of strong ammonia (26° Baume) and dilute with three or four parts of water. Add ammonia to the paste, and stir. This makes a deep blue solution. Add water to make fifty gallons.

Copper carbonate.—For use in the above formula, it may be secured as a green powder, or may be prepared as follows: Dissolve twelve pounds of copper sulfate in twelve gallons of water in a barrel. Dissolve fifteen pounds of sal-soda in fifteen gallons of water (preferably hot). Allow the solution to cool; then add the sal-soda solution to the copper-sulfate solution, pouring slowly in order to prevent the mixture from working up and running over. A fine precipitate is formed which will settle to the bottom if allowed to stand over night. Siphon off the clear liquid. Wash the precipitate by adding clear water, stirring, and allowing to settle. Siphon off the clear water, strain the precipitate through muslin, and allow it to dry. This is copper carbonate. The above amounts will make about six pounds.

Copper sulfate.—See Sulfate of copper.

Corrosive sublimate (mercuric chloride).—Used for disinfecting pruned stubs and cleaned-out cankers, at the rate of one part in 1,000 parts of water. Can be secured from the druggist in tablet form in vials of twenty-five each, and costing 25 cents. One tablet makes a pint of solution. Make and store solution in glass and label "poison.”

Formaldehyde (40 per cent solution of formaldehyde gas in water).—A pungent, clear liquid, very irritating to eyes and nose. Obtained at any drugstore at about 40 cents a pint. Used for potato-scab, oat smut, bunt in wheat, soil disinfection, and so on.

Lime.—Offered for sale in the following forms: (a) Ground rock or ground limestone; air-slaked time is of the same composition, i.e. a carbonate of calcium. (6) Lump, barrel, stone, or quicklime; this is burned limestone, and should test at least 90 per cent oxide of calcium, (c) Prepared, ground, or hydrated time; this is water- or steam-slaked quicklime, dried and pulverized. Used as an applicant to the soil to correct acidity, for club-root of cabbage, and for preparing spray mixtures.

Lime-sulfur.—In the many possible combinations, lime-sulfur is coming to be equally as important as bordeaux mixture, in the control of many plant diseases.

(1) Flowers of sulfur or very finely powdered sulfur is often dusted on plants for surface mildews.

(2) A paste of equal parts of lime, sulfur, and water. This is painted on the heating-pipes in the greenhouse, and is valuable for keeping off surface mildews.

(3) Home-boiled dilute lime - sulfur. This solution has been widely used in the past as a dormant spray, particularly for San Jose scale and peach leaf-curl. It is likely to be supplanted by (4) or (5). For preparation see page 1043.

(4) Home-boiled concentrated lime-sulfur. —When a great deal of spraying is to be done, a concentrated lime - sulfur solution may be boiled at home and stored in barrels to be used as needed. For method of preparation see page 1043.

Test with a Baume hydrometer, which has a scale reading from 25° to 35°. Dilutions are reckoned from a standard solution testing 32°. If the solution tests only 28°, it is not so strong as standard, and cannot be diluted so much as a solution testing 32°. The table shows the proper dilution for solutions testing 25° to 35° Baume:

1-10 1-15 1-20 1-25 1-30 1-40 1-50 1-60 1-75 1-100
25° 7.4 11 14.7 18.4 22.1 29.5 36.8 44.2 55 73
26" 7.7 11.6 15.4 19.3 23.2 30.9 38.6 46.3 58 77.2
27° 8.1 12.1 16.1 20.2 24.3 32.4 40.5 48.5 60.6 80.7
28° 8.4 12.7 16.9 21.1 25.4 33.8 42.3 50.7 63.5 84.5
29° 8.8 13.2 17.6 22.1 26.5 35.3 44.2 53 66.3 88.2
30° 9.2 13.9 18.4 23 27.6 36.9 46.1 55.3 69 92
31° 9.6 14.4 19.3 24 28.8 38.4 48 58 72 06
32° 10 15 20 25 30 40 50 60 75 100
33° 10.4 15.6 20.8 26 31.2 41.5 52 62.4 78 104
34° 10.8 16.2 21.6 26.8 32.4 43.2 54 64.7 80.8 108
35° 11.2 16.8 22.4 28 33.4 44.9 56 67.4 84.2 113

Decimals are given in all cases, but for practical purposes the nearest even gallon or half gallon can be used, unless appliances for more accurate measurement are at hand. It is understood in making all dilutions that water is added to one gallon of the concentrate to make the stated amount. Do not measure out the stated amount of water and add the concentrated solution to it.

(5) Commercial concentrated lime-sulfur.—As manufactured and placed on the market is a clear amber liquid, and should test 32° to 35° Baume. It costs about 20 cents a gallon retail, and comes ready to pour into the spray tank. For apple and pear diseases. Arsenate of lead can be used with this solution, and increases its fungicidal value.

(6) Scott's self-boiled lime-sulfur.—This is a mechanical mixture of the two substances, and is really not boiled, the heat being supplied by the slaking lime. In a small barrel or keg place eight pounds of good quicklime. Add water from time to time in just sufficient amounts to prevent burning. As soon as the lime begins to slake well, add slowly (preferably through a sieve) eight pounds of sulfur flour. Stir constantly, and add water as needed. As soon as all bubbling has ceased, check further action by adding a quantity of cold water, or pour into a barrel or tank and make up to fifty gallons. Keep well agitated. Very effective against peach scab and brown rot. Several other formulas have been used: 10-10-50 and 5-5-50. Arsenate of lead can be used with this mixture.

By using boiling water and allowing the hot mixture to stand for half an hour, a stronger spray mixture than the above can be secured. It cannot be used safely on peaches, but has been used successfully on grapes for surface mildew. The addition of sulfate of iron or sulfate of copper, one or two pounds to fifty gallons, has been used for apple rust.

Potassium sulfid (liver of sulfur).-Simple solution, three ounces in ten gallons of water. For mildew in greenhouses, on rose bushes and other ornamentals.

Resin-sal-soda sticker.—Resin, two pounds; sal-soda (crystals), one pound; water, one gallon. Boil until of a clear brown color, i.e. from one to one and a half hours. Cook in an iron kettle in the open. Add this amount to fifty gallons of bordeaux. Useful for onions, cabbage, and other plants to which spray does not adhere well.

Sulfate of copper (blue vitriol).—Dissolve one pound of pure sulfate of copper in twenty-five gallons of water. A specific for peach leaf-curl. Apply once before buds swell in the spring. Cover every bud. For use in preparing bordeaux mixture. Costs from 5 to 7 cents a pound, in quantity.

Sulfate of iron (copperas).—A greenish granular crystalline substance. Dissolve one hundred pounds in fifty gallons of water. For mustard in oats, wheat and the like, apply at the rate of fifty gallons an acre. Also for anthracnose of grapes as a dormant spray.

Sulfur (ground brimstone, sulfur flour, flowers of sulfur).— Should be 99 per cent pure. Valuable for surface mildews. Dust on dry or in the greenhouse used in fumes. Evaporate it over a steady heat, as an oil-stove, until the house is filled with vapor. Do not heat to the burning point, as burning sulfur destroys moat plants. To prevent burning, place the sulfur and pan in a larger pan of sand and set the whole upon the oil-stove. Donald Reddick.

Catalogue of diseases.

Abies. Witches' Broom (Aecidium elatinum. Melampsorella elatina).—On fir causing swellings, cankers, and witches' brooms. Control.—Prune off all affected parts.

Abutilon. Rust.—See under Hollyhock.
Contagious Chlorosis.—Variegated leaves.
Control.—Remove variegated leaves and their shoots, keep in dark and remove any further variegated leaves; then the plant should remain green.

Acacia. Rusts (Aecidium sp.).—Distorts branches and twigs.
Control.—Prune off diseased parts.

Acer. Tab-spot (Rhytisma acerinum).—Black tar-like spots on upper side of the leaves.
Control.—Burn all old leaves in fall or winter. Sun Scald or Scorch.—Maples suffer commonly from a drying up of the foliage, due to over-transpiration of water at times when hot winds occur.

Actinidia. Mildew (Uncinula necator).—See under Ampelopsis.

Aesculus. Leaf-spot (Phyllosticta paviae).—Irregular spots develop rapidly, the larger part of the
leaf being involved. Leaves fall prematurely.
Control.—Spray with bordeaux mixture, beginning when the leaves are about half-grown and repeating the process every three weeks.

Agave. Leaf-blotch (Coniothyrium concentricum).—Grayish, more or less circular dead patches, ranging from ½ to 1 inch in diameter.
Control.—Remove and burn diseased leaves.

Allium.—See under Onion.

Almond. Blight. (Coryneum beyerinkii).—See Peach Blight.
Yellows.—See under Peach.

Alnus. Root-tubercles.—Clumps of small tubercles on the roots.
Not important.
Witches' Brooms and Bladdery Deformations Of Flowers (Exoascus sp.—Broom-like tufts of branches and irregular deforming and contortion of fruits.
Control.—See under Peach Leaf-Curl.

Alyssum. Mildew (Erysiphe polygoni).—See under Verbena.
Disease very similar.

Amarantus. White "Rust" or Mildew (Albugo bliti).—See similar disease under Radish.

Amelanchier. Rust (Gymnosporangium sp.).—Orange rust spots on leaves.
Control.—Keep junipers at a considerable distance.
Witches' Broom (Dimerosporium collinsii).—Thick twisted broom-like growth of branches.
Control.—Cut out the brooms.

Ampelopsis. Black-rot.—See under Grape.
Mildew (Uncinula necator).—Powdery mildew growths on upper side of leaf.
Control.—Dust with sulfur.

Anemone. Root-decay (Sclerotinia tuberosa).—Rhizomes decayed and large lumps form on the outside.
Control.—Eradicate affected rhizomes and the cup-like fungous bodies near such plants.
Rust.—Several rusts attack species of Anemone.

Anthurium. Bliqht (Glomerella cincta).—See under Orchids.

Apple. Blight.—The same disease as Pear Blight, which see.
Canker.—Smooth cankers in bark of trunk or limbs usually indicate blight (Bacillus amylivorus); rough ones, New York apple-tree canker (Sphaeropsis malorum), or the nail-head canker (Numularia discreta).
Control.—As soon as noticed, cut away dead bark and wood to the living tissue and paint over with lead paint or coal-tar.
Scab (Venturia inaequalis).—Oliver-green, brownish or blackish scab-like spots on leaves and fruit.
Control.—Rake and burn or plow under old leaves very early in spring. Spray with lime-sulfur 32° Baume, 1-40, or bordeaux, 3-3-50: (1) when blossom buds show pink; (2) when majority of petals have fallen: (3) three weeks after 2, depending upon the weather; (4) if a late attack is feared, spray before fall rains begin.

Apricot. Yellows.—See under Peach.
Black-spot or Scab.—See under Peach.

Aquilegia. Mildew (Erysiphe polygoni). — See under Verbena.
Disease very similar.
Black-spot (Bacillus delphini),—Sunken black spots on leaves and stems.
Control.—Remove and burn diseased parts.

Artemisia. Rust (Puccinia asteris).—Same rust as on Asters, which see.

Artichoke. Soft-rot.—See under Carrot.

Arum. Leaf-spot (Protomyces ari).—Irregular bleached patches on leaves and leaf-stalks of A. maculatum.
Control.—Burn diseased plants.

Asparagus. Rust (Puccinia asparagi).—A rust of the tops which is often so severe as to kill them, thus interfering with root- development.
Control.—Dust with flowers of sulfur about every three weeks while dew is still on in the morning. Use dusting- machines.

Aspidistra. Leaf-blotch (Ascochyta aspidistrae).—Large, irregular, bleached spots with black streaks running across.
Control.—Remove diseased leaves.

Aster. Rust (Puccinia asteris).—Brown rust of leaves.
Control.—Eradicate the affected leaves.

Aucuba. Freezing.—Young leaves suffer from spring frosts.

Auricula. Leaf-blotch (Heterosporium auriculi).—Three or four olive-green spots on each leaf. Spots become brown and fall out.
Control.—Do not have excessive moisture. Spray with potassium sulfid and ventilate well.

Avocado, or Persea. Anthracnose (Colletotrichum gloeosporioides). —See under Pomelo.

Bamboo. Smut (Ustilago shiriana).—Internodes and tips of young shoots attacked. Wild and cultivated bamboo attacked in Japan.
Control.—Bordeaux mixture and sprinkling soil with lime before the shoots appear.

Banana. Rot (Bacillus musae).—Leaf-blades droop, turn yellow; petioles decay, letting leaves drop, and finally whole plant rots to the ground.
Control.—Practise sanitation.

Bean. Anthracnose, or Pod-spot (Colletotrichum lindemuthianum). —Reddish brown, scab-like spots on stems, pods, and veins of leaves, particularly on yellow-podded snap beans. Fungus enters the Deans.
Control.—Use seed only from pods without spots. Spray plants, from beneath and above, every ten days.
Blight (Bacterium phaseoli).—Large papery spots on leaves and watery spots on pods.
Control.—As for Anthracnose.

Beet. Heart-rot (Phoma betae).—Leaves appear spotted late in July, then wilt, and finally a dry heart-rot appears.
Control,—Destroy affected plants. Practise long rotations. Treat seed with formalin, one pint in thirty gallons of water. Scab.—The same disease as Potato Scab, which see.

Begonia. Root-rot (Thielavia basicola),—See under Nicutiana.

Berberis. Rust (Puccinia graminis).—Orange-colored rust spots on under side of leaf.

Betula. Leaf-spot (Gloeosporium betularum).—Round spots with blackish margin.
Heart-rot (Fames igniarius).—See under Fagua.

Blackberry. Crown-gall, or Root-gall (Bacterium tumefaciens). —Swellings, hard or soft, on roots and stem below ground.
Treatment.—Plow up and burn all bushes in a diseased patch. Plant clean roots in a new place. Anthracnose.—See under Raspberry.
Red or Orange Rust.—See under Raspberry.
Leaf-spot.—See under Dewberry. Same disease.

Blueberry. Rust (Calyptospora goeppertiana).—Stem attacked, swollen, spongy, at first pink, changing to brown and blackish. Plants taller than healthy and leaves dwarfed.
Control.—Segregate from species of fir and spruce.

Brassica. See under Cabbage.

Brussels Sprouts. Club-root.—See under Cabbage.

Buxus. Stem-blight (Nectria rousseliana).—Twigs killed, reddish pustules appearing on stems and leaves.
Control.—Remove all diseased parts and burn.

Cabbage. Club-root, or Club-Foot (Plasmodiophora brassicae).— A contorted swelling of roots and sickly wilted tops.
Control.—Destroy affected seedlings. Lime the soil at least eighteen months before planting cabbage, using at the rate of two tons of quicklime to the acre.
Black-rot (Bacillus campestre).—Sap-tubes in leaves and stem turn black and the leaves drop, thus preventing heading.
Control.—Practise crop-rotation. Soak the seed for fifteen minutes in a solution of mercuric chloride, one tablet in a pint of water.

Cactus. Spot (Diplodia opuntiae).—Sometimes a serious disease.

Calathea. Leaf-blight (Cephaleurus parasiticus).—The epidermal cells contain the alga, which spreads over the leaf, blackening and killing it.
Control.—Remove diseased leaves.

Calceolaria. Leaf-blight (Ascribed to a Micrococcus).—Brownish patches on lower leaves, many times bordered by the small veins of the leaf.
Control.—Burn affected plants.

Campanula. Rust (Coleosporium campanulae).—Red and brown rust spots on leaves.
Control.—Segregate from Pinua rigida.

Capsicum. Anthracnose.—Same as on Piper, which see.

Carnation. Rust ( Uromyces caryophyllinus).—Brown, powdery pustules on stems and leaves.
Control.—Spray once in two weeks with a solution of copper sulfate, one pound to twenty gallons of water. Pick off diseased leaves. Keep temperature low.

Carpinus. Black-mold (Dimerosporium pulchrum).—On leaves.
Control.—Spray with any good fungicide.
Heart-rot (Fomes fulvus).—Red-brown decay; crumbles when crushed.
Control.—Surgery methods.

Carrot Soft-rot (Bacillus carototorus).—A soft-rotting of the root identical with the soft rots of other root crops.
Control.—Good drainage of soil. Steam sterilization of soil.
Leaf-spot or Early Leaf-blight (Cercospora apii).—See under Celery.

Carya.—See under Hickory-Nut.

Castanea.—See under Chestnut.

Catalpa. Leaf-blight.—Sudden blackening and dying of leaves in early summer.
Heart-Rot (Polystictus versicolor),—Heart -wood becomes straw-colored and finally soft.
Control.—Surgery.
Root-rot of seedlings (Thielavia basicola).— See under Nicotiana.

Cauliflower.—See under Cabbage.

Celastrus. Mildew (Phyllactinia corylea).—Powdery mildew of leaves.
Control.—Dust with sulfur.

Celery. Earlt Leaf-blight (Cercospora apii).—A spotting and eventual blighting of leaves.
Control.—Spray with ammoniacal copper carbonate, 5-3-50, beginning in seed-bed and keeping new growth covered throughout the season.
Late Blight (Septoria petroselini var. apii).—Blight of foliage appearing late in season and in storage.
Control.—As above. Grow under half shade.

Celtis, Mildew (Peronoplasmopara celtidis).—Definite spots on veins, water-soaked dark green becoming gray.
Control.—Spray with bordeaux mixture.

Cercis. Leaf-spot (Ascochyta pisi).—Spots round, yellowish with brown margin on leaves and stem.
Control.—Spray with dilute bordeaux mixture on first appearance.

Chamaecyparis. Twig Disease (Pestalozzia funerea).—Bark of young branches killed, needles die.
Control.—Prune off affected parts and clean up Utter and burn.
Heart-rot (Steccherinum ballonii).—Kills tops of trees.

Chard (Beta). Leaf-spot (Cercospora beticola).—Brown, purplish bordered spots on leaves.
Control.—Pick off and destroy diseased leaves. Cherry.
Brown-rot (Sclerotinia fructigena).—The flowers decay, the leaves become discolored with irregular brown spots, and the fruit rots on the tree.
Control.—Spray with bordeaux mixture, 4-4-50, or lime- sulfur, 1-40 (1) just before the blossom buds open; (2) just after the blossoms fall; (3) one or two more applications at intervals of ten days.
Powdery Mildew (Podosphaera oxycanthae).—Leaves and twigs affected, often causing defoliation.
Control.— Spray with lime-sulfur, 1-40, or dust heavily with powdered sulfur.
Black-knot. —See under Plum. Same disease.

Chestnut Canker, or Bark Disease (Endothia parasitica).— Sunken or swollen cankers on limbs or trunk. Limbs die and leaves and burs cling in winter.
Control.—Remove diseased parts and burn. Paint all wounds. Little chance of saving trees in infested locality.

Chicory. Stem-spot (Pleospora albicans).—Yellowish-gray spots on lower portion of the stem. Later on smaller branches and leaves. Plant destroyed.
Control.—Eradicate diseased plants.

Chrysanthemum. Leaf-spot (Septoria chrysanthemi).—Small dark brown spots, which increase in size until leaf is killed.
Control.—Pick and burn affected leaves. Spray with bordeaux mixture, 4-4-50.
Rust (Puccinia chrysanthemi).—Reddish brown rust pustules on leaves.
Control—As for Leaf-Spot.

Cineraria. Mildew (Bremia lactucae).—Plants stunted and of a pale color, finally wilting. Same disease on lettuce.
Control.—Remove diseased plants. Do not use same soil again.
Rust.—See under Senecio.

Citrus.—See under Orange, Lemon, Grapefruit, etc. The "wither tip" disease described under Pomelo is common to species of citrus.

Clematis. Leaf-spot (Cylindrosporium clematidis var. jackmanii).
—Causing loss of lower leaves at times. Not serious.

Cocoanut. Bud-rot (Bacillus coli).—Rot of soft tissues of coconut plant and is perhaps responsible for coconut bud-rot.
Control.—Not given.

Coffea. Leaf-disease (Hemileia vastatrix and H. woodii).— Circular discolored areas, turning pale yellow and becoming studded with orange-yellow spots.
Control.—Burn all diseased leaves.

Colchicum. Rust (Uromyces colchici).—Black spots on leaves. Looks like a smut disease.
Control.—Diseased leaves should be burned.

Colocasia. Root-rot (Peronospora trichomata).—Sap-tubes turn yellow and finally entire tuber becomes black.
Control.—Dry tubers thoroughly before storing. Do not plant in soil in which the disease has occurred.

Convolvulus. Mildew (Albugo ipomoeae-panduranae),—Distortions and white or yellow blisters.
Control.—Remove diseased plants and spray with bordeaux mixture frequently.

Cordyline. Blight.—See under Orchids.

Coreopsis. Mildew (Sphaerotheca humuli var. fuliginea).—Powdery mildew of the leaves.
Control.—Dust with sulfur.

Corn. Smut (Ustilago zeae).—Boils on stalks, ears or tassels, at first white, then black, and, when burst open, containing black powder, the spores.
Control.—Cut out developing smut-boils and burn.
Wilt (Pseudomonas stewartii).—Sap-tubes turn yellow and plant wilts and drys up.
Control.—Burn affected plants. Grow varieties not affected.

Cornus. Twig-blight (Diaporthe albocarnis).—Twigs die, bark turns yellow and is covered with numerous small pimples.
Control.—Prune off and destroy affected parts.

Corylus.—See under Filbert.

Cosmos. Stem-blight (Phomopsis stewartii).—Brown spots rapidly enlarging on stems of mature plants. Parts above wilt and die.
Control.—Difficult and no certain methods known. Remove diseased stems and burn.

Cotoneaster. Rhus (Gymnosporangium clavariaeforme).—Orange rust pustules on leaves.
Control.—Keep at a distance from junipers.

Cranberry. Blast, or Scald (Guignardia vaccinii).—Young flower and fruits bloated, older fruits appear scalded or watery.
Control.—Spray five or six tunes with bordeaux mixture. 5-5-50, to which has been added four pounds of resin fish-oil soap. Begin just before the blossoms open.

Crataegus. Rust (Gymnosporangium sp.).—Orange rust pustules on leaves and petioles.
Control.—Keep at a distance from junipers.

Cress. White Mold.—See under Horse-Radish.

Crocus. Root-rot (Rhizoctonia sp.).—Important in France and likely occurring here.
Control.—Sanitation, new soil frequently or soil sterilization.

Cucumber. Blight, or Mildew (Pseudoperonospora cubensis).— A blighting and premature yellowing of the leaves.
Control.—Spray with bordeaux mixture, 5-5-50, every ten to fourteen days after plants begin to run. Wilt.—See under Cucurbita.

Cucurbita. Wilt (Bacillus tracheiphilus).—Sap-tubes are clogged and destroyed, causing the plant to wilt.
Control.—Eradicate the striped beetle. Gather and destroy all wilted leaves and plants.

Cupressus. Root-rot.—See under Pine. Same disease.
Twig Disease.—See under Chamaecyparis.
Witches' Broom (Gymnosporangium ellisii).—Fasciation of branches.
Control.—Prune off affected parts.

Currant. Wilt, or Cane-blight (Botryosphaeria ribis).—Canes die suddenly, the leaves wilting.
Control.—No satisfactory method known. Cut out and burn affected plants.
Rust (Cronartium ribicola).—Brown rust pustules and brown felt-like growth on under side of leaf. Black currants especially susceptible.
Control.—Grow at least 500 feet from white pine trees.

Cycas. Leap-spot (Mycosphaerella tulasnei=Cladosporium herbarum).—Gray spots and final death of leaves.
Control.—Remove and burn affected parts.

Cyclamen. Leaf-spot (Glomerella rufomaculans var. cyclaminis). —Spots circular, slightly water-logged, with sharply defined outlines.
Control.—Destroy affected leaves by burning.
Blight.—Similar to Lilium Leaf-Spot, which see.

Dahlia. Wilt (Sclerotinia sclerotiorum).—White mold on stem, later yellowing and wilting of plant, and finally stem collapses. Control.—Remove and burn affected plants. Green stable manure favors the disease.

Daphne, Leaf-spot (Mycosphaerella laureolae),—Similar to Strawberry Leaf-Spot, which see.
Date. See under Palms.

Delphinium. Black-spot (Bacillus delphini).—Sunken black spots on stem and leaves.
Control.—Remove and burn diseased parts.

Dewberry. Leaf-spot (Septoria rubi).—Small pale spots of dead leaf-tissue finally becoming dotted with black specks.
Control.—No successful method of treatment is known.

Dianthus.—See under Carnation.

Digitalis. Mildew (Peronospora sordida).—Broadly effused, dingy lilac patches of mildew on under surface of leaves.
Control —Spray with bordeaux mixture.

Diospyros. Mildew (Podosphaera oxyacanthae).—Powdery mildew of the leaves.
Control.—Dust with sulfur.

Dracaena. Blight.—See under Orchids.

Eggplant. Anthracnose (Gloeosporium melongenae),—Spots on fruit. Same as on Piper, which see.
Stem Rot (Nectria ipomoeae).—Spreading spots on the stem.
Control.—Spray mixtures may be of avail.

Elaeagnus. Root-tubercles.—See under Alnus. Not destructive

Endive. Rust (Puccinia endiviae).—Rust spots on leaves.
Stem-rot.—See under Chicory.

Eucalyptus. Tumor ( Ustilago vriesiana).—Woody tumors at collar of tree. Production of black soot-like muss of spores between wood and bark.
Control.—Surgery methods.

Euphorbia. Blight (Gloeosporium euphorbiae).—Causes death of floral portion just before flowering time and the parts below are noon blighted.
Control.—Burn affected plants. Spray with bordeaux mixture.

Fagus. Heart-Rot (Fomes igniarius).—White, dry, and somewhat solid decay of heart-wood bordered by fine black lines. Control.—See under Arboriculture, Diseases of Trees.

Ferns. Tip Blight (Phyllosticta pteridis).—Brown spots at or near tips of the fronds covered with minute black dots.
Control.—Remove and burn the blighted leaves and then spray with bordeaux mixture.

Ficus. Leaf-spot (Leptostromella elasticae).—Causes spots on leaves. See also under Fig.

Fig. Leaf-spot (Cercospora bolleana).—Brown spots on leaves. Leaves turn yellow and drop off.
Control.—Spray with bordeaux mixture while leaves are young.

Filbert. Black-knot (Cryptosporella anomala).—Serious stem disease, canker girdles the stems and kills parts above.
Control.—Prune off affected parts and burn.

Forsythia. Leaf-spot (Alternaria forsythiae).—Forms sub-circular spots.
Control.—Spray with bordeaux mixture.

Fraxinus. Rust (Puccinia fraxinata).—Swellings of midribs of leaves and petioles with orange nut spots on them.
Control.—Keep the common grass Spartina cynosuroides away from the trees.

Freesia. Leaf-spot and Wilt (Heterosporium gracile).—Large brown spots with darker margin, numerous; soon the leaves wilt and die.
Control.—Spray with ammoniacal copper sulfate.

Galanthus. Decay (Sclerotinia galanthi).—In place of the flower a shapeless moss is produced covered with brown mildew. Tubers decay also.
Control.—-Remove all affected parts and burn. Use new soil thereafter.

Gardenia. Rust.—See under Coffea. Same disease.

Genista. Root-tubercles.—Beneficial.

Gentiana. Rust (Puccinia gentianae).—Lower leaves first attacked, become yellow and die. Disease gradually works upward.
Control.—Destroy affected plants.

Geranium. Mildew (Plasmopara geranii).—Downy mildew of leaves.
Control.—Spray with bordeaux mixture.

Gladiolus. Smut (Urocystis gladioli).—Black smut pustules on corms.
Control.—Destroy affected corms. Use new soil.

Gleditsia. Leaf-spot (Leptostroma hypophylla).—Leaflets become covered with small black specks, causing some of them to turn yellow and fall.

Gooseberry. Mildew (Sphaerotheca mora-uvae).—A powdery mildew of the fruit and young growth of English varieties.
Control.—-Spray with potassium sulfide, one ounce to two gallons of water, at intervals after leaves begin to unfold.

Grape. Black-rot (Guignardia bidwellii).—Brown circular spots on leaves, black, elongated, sunken pits on petioles, canes, etc., and on the berry a brown rot with shriveling and wrinkling.
Control.—Spray with bordeaux mixture, 4-1-50, before rains. Spray (1) when the third or fourth leaf unfolds; (2) as soon as the blossom- have fallen; (3) when berries are size of a pea; (4) about two weeks later. Two more applications if wet season.
Downy Mildew, or Leaf-blight (Plasmopara viticola).—White frost-like patches on under side of the leaf.
Control.—Some as Black-Rot.

Grapefruit. Leaf-spot (Pestalozzia guepini).—Large spots with dark margins. Leaves fall prematurely. On other species of Citrus also.
Control.—Destroy affected leaves.

Guava. Anthracnose (Glomerella psidii).—Circular brown, decayed areas on fruit. Like apple bitter-rot.
Control.—None given.

Hedera. Leaf-spot and Leaf Blight (Vermicularia trichella).— Rapid blackening of the etiolated portion of the leaf.
Control.—Remove and burn affected leaves and spray with bordeaux mixture.

Helianthus. Rust (Puccinia helianthi).—Red rust pustules on leaves of most species of Helianthus.
Control.—No specific control measures worked out.

Helleborus. Leaf-blotch (Coniothyrium hellebori).—Large circular brownish blotches of scorched appearance, covered with minute black dots.
Control.—Cut off and burn affected leaves.

Hemerocallis. Leaf-spot.—See under Freesia.

Hibiscus. Leaf-spot (Phyllosticta idaecola).—Indistinct brown spots with whitish centers.
Control.—Burn affected leaves.
Mildew (Microsphaera euphorbiae).—Powdery mildew of leaves.
Control.—Dust with sulfur.

Hickory-nut. Leaf-spot (Marsonia juglandis).—Large leaf-spot, causing premature dying of leaves.
Control.— Spraying with bordeaux mixture may be of value.

Hollyhock. Rust (Puccinia malvacearum).—All parts of plant show reddish brown pustules.
Control.—Eradicate mallow. Pick off diseased leaves and burn. Spray every week with bordeaux mixture, 4-3-50.

Horse-Radish. White Mold (Cystopus candidus).—Deforming and swelling of leaves and stems, with white powdery surface growth.
Control.—Hardly important enough on the radish to necessitate control.

Hyacinthus. Blight (Pseudomonas hyacinthi).—Serious pest in the Netherlands. Sap-tubes filled with yellow slime.
Control.—Destroy all affected plants.

Hydrangea. Leaf-blight (Phyllosticta hydrangeae).—Leaf-spot disease which becomes serious at times.
Control.—Destroy diseased leaves as soon as noticed.

Iberis. Club-root.—Sec under Cabbage.

Impatiens. Mildew (Plasmopara obducens).—Downy mildew of the leaves.
Control.—Remove affected leaves and spray with bordeaux mixture.

Ipomoea. Robt (Coleosporium ipomoeae).—Common rust spotting of leaves.
Control.—Destroy affected leaves.
Mildew.—See under Convolvulus.

Iris. Leaf-blight (Botrytis galanthina).—First the leaves and flowers are much distorted and covered with black mold growth; later the bulb may be destroyed.
Control,—Eradicate diseased plants and grow in new soil.

Juglans. Leap-spot (Gnomonia leptostyla).—Brown leaf-spot, causing defoliation.
Control.—Collect and burn fallen leaves. Spray with bordeaux mixture while leaves are young.

Juniperus. Cedar Apples (Gymnosporangium spp.).—Large or small red and woody growth at tips of branches. Gelatinous in wet weather.
Control.—Prune off affected parts. Keep apples, pears, and hawthorns at a distance.

Kale. Black-rot.—See under Cabbage.

Kohlrabi. Club-root.—See under Cabbage.

Laburnum. Leaf-spot (Peronospora cystisi).—Leaves become brown-spotted. Seedlings killed.
Control.—Spray with bordeaux mixture.
Contagious Chlorosis.—See under Abutilon.

Larix. Canker (Dasyscypha willkomii).—Canker of trunk and branches, usually around base of trunk.
Control.—Eradicate diseased parts, using tree surgery methods.

Laurus. Witches' Broom (Exobasidium lauri).—Branched out growths, antler-like, 2 or 3 feet in length, springing from the leaves.
Control.—Prune off affected parts.

Lemon. Brown-rot (Pythiacystis citrophthora).—White mold on surface of fruit.
Control.—Not destructive in orchard. Add copper sulfate to water when washing lemons to prevent infection of healthy ones.

Leaf-diseases.—Not well understood. Probably controllable by spraying.

Lespedeza. Mildew (Microsphaera diffusa).—Powdery mildew of leaves.
Control.—Dust with sulfur.

Lettuce. Drop, or Rot (Sclerotinia libertiana).—Base of stems or leaves rots off, allowing leaves to drop.
Control.—Sterilize soil with steam before planting.
Mildew.—See under Cineraria.

Ligustrum. Anthracnose (Gloeosporium cingulatum).—Affected areas light brown cither oblong on one side of the stem or completely girdling it.
Control.—Destroy by burning affected plants.

Lilium. Leaf-spot (Botrytis sp.).—Orange-brown or buff blotches on leaves, stem and flowers of L. candidum. May be same as Tulipa Mold, which see.
Control.—-Eradicate diseased plants.

Lily-of-the-Valley. Stem-rot.—See under Paeonia.

Liriodendron. Twig Blight (Myxosporium longisporium.).—Killing twigs.
Control.—Prune off diseased twigs.

Lobelia. Canker (Phoma devastatrix).—Portions of the stems covered with minute black dots.
Control.—Remove diseased plants. They never bloom.

Lonicera. Canker (Nectria cinnabarina).—Rough canker on limbs covered with flesh-colored or red bodies.
Control.—-Prune off or cut out all affected parts and cover wounds with tar.

Lupinus.—See under Pea.

Lychnis. Smut (Ustilago violacea).—Pollen-sacs filled with black dust which escapes and discolors the flower.
Control.—Destroy the affected plants and use new soil.

Lycopersicum.—See under Tomato.

Magnolia. Leaf-spot.—See under Grapefruit.

Malva. Rust.—See under Hollyhock. Same disease.

Mangifera. Black Blight (Dimerosporium mangiferum).—Intense black velvety patches on both surfaces of the leaves.
Control.—Spray with any good spray mixture.

Matthiola. Club-root.—See under Cabbage.

Mentha. Rust (Puccinia menthae).—A most destructive rust disease.
Control.—None given.

Mignonette. Leaf-spot (Cercospora resedae).—First reddish discoloration of leaves. Later small depressed spots with brownish or yellowish margin.
Control.—Spraying with bordeaux mixture gives good results.

Morus. Leaf-spot (Cercospora moricola).—Not serious.
Leaf-blight (Pseudomonas mori).—Wilting and death of leaves. Cankers girdle the twigs.
Control.—Prune off diseased parts and burn.

Muscari. Smut (Urocystis colchici).—Long black powdery streaks on leaves.
Control.—-Destroy affected plants by burning. Use new soil.

Mushroom. Mold (Mycogone perniciosa).—Mushrooms develop abnormally as monstrous soft growths. These develop into a moldy mass and putrify.
Control.—Affected beds should be thoroughly cleaned and sprayed with copper sulfate, one pound to fifty gallons of water.

Muskmelon. Downy Mildew.—See under Cucumber.
Wilt.—See under Cucurbita.

Narcissus. Leaf-spot (Ramularia narcissi).—Spots on leaves and stem.
Control.—Burn diseased parts and spray with bordeaux mixture.

Nasturtium. White "Rust." (Cystopus candidus).—See under Horse-Radish.

Nectarine. Yellows, etc.—See under Peach.

Nerium. Black Mold (Capnodium foedum).—Black velvety-like growth on leaves.
Control.—Spray with bordeaux mixture.

Nicotiana. Root-Rot (Thielavia basicola).—Blackening and rotting of the roots of seedling plants.
Control.—Steam sterilization of seed-beds.
Mosaic or Calico Disease.—Enzymic disease. Mottling of leaf. Spread by touch.

Oak. Anthracnose (Gnomonia veneta).—Brown spotting on under side of leaves, along veins. Brown pustules on spots. Death of leaves and twigs. See under Arboriculture, Diseases of Trees.
Control.—Collect and burn all diseased twigs and leaves. Spray with bordeaux mixture frequently from time buds swell.

Oenothera. Leaf-galls (Synchytrium fulgens).—Yellow swellings on the leaves.
Control.—Destroy affected leaves.

Okra.—See under Hibiscus.

Olive. Limb-gall, or Knot (Pseudomonas oleae).—Knots or galls on the twigs and limbs.
Control.—Remove and burn affected limbs.

Onion. Mildew (Peronospora schleideniana).—Causes a wilt or blight of the leaves.
Control.—Spray with bordeaux mixture, 5-5-50, to which has been added one gallon of resin sal-soda sticker. First application when third leaf has developed, repeating every ten days until harvest time.
Smut (Urocystis cepulae).—Black pustules on leaves and bulbs. Seedlings may be killed outright.
Control.—Grow seed in new soil. Drill in with the seed one hundred pounds of sulfur and fifty pounds of air-slaked lime to the acre.

Opuntia. Spot (Diplodia opuntia).—Sometimes a serious pest of cactus.

Orach. Galls (Urophlyctis pulposa).-Glassy swellings on leaves, stems and flowers of Chenopodium
and Atriplex.
Control.—Burn affected plants.

Orange. Black-mold (Capnodium citri).—Black mold-like growth on leaves and fruit.
Control.—Spray with any good fungicide.

Orchids. Leaf-blight (Glomerella cincta).—Leaf dies back from the tip, turning brown.
Control.—Burn affected leaves. Spray frequently then with bordeaux mixture.

Ornithogalum. Warts (Synchytrium niesii).—Dirty white warts on leaves, bounded by a dark line. Control.—Burn diseased leaves.

Paeonia. Stem-rot and Wilt (Sclerotinia paeoniae).—Gradual wilting and dying of leaves caused by decay of stem at or near surface of soil.
Control.—Spray the stems frequently with a strong fungicide. Burn affected plants.

Palms. Leaf-spot (Gloeosporium allescheri}.—May cause ultimate death of leaves.
Control.—Frequent spraying with bordeaux mixture and eradication of diseased leaves may prove beneficial.

Pandanus. Black Canker (Nectria pandani).—Kills branches and entire plants. Black pustules on bark oozing black tendrils.
Control.—Cut out diseased portions as noon as noticed.

Pansy. Leap-spot (Peronospora violae).—Discolored spots with pale violet growth on them.
Control.—Spray with bordeaux mixture.

Papaver. Mildew (Peronospora arborescens).—Downy mildew of wild and cultivated poppies. Especially injurious to seedlings of garden species.
Control.—Spray with bordeaux mixture.

Parsley. Leaf-scorch (Septoria petroselini).—Small scattered brown patches, which increase in size until whole leaf is covered.
Control,—Spray early with dilute bordeaux. Pick off and burn affected leaves.

Parsnip. Leaf-blight.—See under Celery, Early Leaf-Blight.

Pea. Mildew (Erysiphe polygoni).—A powdery mildew on pods and leaves.
Control.—Dust dry sulfur over the plants.

Peach. Blight (Coryneum beyerinkii).—A spotting, gumming and death of the buds and twigs, particularly in the lower parts of the tree. The fruit drops.
Control.—For California conditions, two applications bordeaux mixture, 6-5-30, or lime-sulfur, 1-10, (1) in November or December, and (2) in February or March. Leaf-curl (Exoascus deformans).—Leaves curl and wrinkle.
Control.—Spray with lime-sulfur, 1-11, before buds swell.
Brown-rot (Sclerotinia fructigena).—Rot on fruit and cankers on limbs.
Control.—Spray with self-boiled lime-sulfur, 8-8-50, adding two pounds arsenate of lead. Spray (I) about time shucks are shedding from young fruit; (2) two or three weeks later; (3) one month before fruit ripens.
Scab, or Black-spot (Cladosporium carpophilum).—Black scab- like spots on fruit.
Control.—Self-boiled lime-sulfur applied as under Brown-Rot.
Yellows.—A fatal disease. Red spots in fruit. Tuft-like growth of new shoots and finally yellow foliage.
Control.—Burn affected trees.

Pear. Blight (Bacillus amylovorus).—Flowers, young fruit, twigs, and leaves turn black and die. Limbs die back and sunken cankers form in bark.
Control.—Eradicate all wild hawthorns, pears and apples. Inspect and remove all blighted parts of tree. Paint wounds with coal-tar.
Scab.—Very similar disease to Apple Scab, which see.

Pecan. Leaf-blotch (Mycosphaerella convexula). — Dark-colored blotches covered with minute black dots on leaves in midsummer.
Control.—None given.

Pelargonium. Dropsy.—Translucent spotting of leaf. Spots finally die.
Control.—Withhold water until absolutely necessary.

Persimmon. Anthracnose (Glomerella rufomaculans).—Similar if not identical to Piper Anthracnose, which see.

Petunia. Wilt.—See under Dahlia.

Phlox. Stem-canker (Pyrenochaeta phloxidis).—Canker just above the ground on the stem. Plant dies; first turning yellow and then falls over.
Control.—Diseased stems should be removed and burned.

Physalis. Wilt (Bacillus solonacearum).—Pith of stem turns brown, sap-tubes filled with viscid ooze.
Control.—Get rid of insects such as potato beetle and burn all affected plants.

Picea. Leaf-spot and Leaf-cast (Phoma sp.).—Causes discoloration and dropping of noodles. Black dots on affected needles.
Control.—Clean up all fallen needles and burn.
Drought Injury.—Drying up of needles. Water in dry weather.

Pine. Root-rot (Armillaria mellea).—Tops turn yellow and die, swelling of trunk at surface of ground. Decay of roots with black threads abundantly present. Toadstools around base of tree.
Control.—Dig up and burn and destroy all toadstools near the affected trees.

Pineapple. Heart-rot.—Browning of the axis of the fruit, due to excessive moisture at time of ripening.
Control.—Keep down humidity in greenhouses.

Piper. Anthracnose (Gloeosporium piperatum).—Spots on leaves of plants. Also apple bitter-rot fungus (Glomerella rufomaculans) causes similar spots on the fruits.
Control.—Frequent spraying with bordeaux mixture,

Platanus. Anthracnose.—See under Oak. Same disease.

Plum. Black-knot (Plowrightta morbosa).—Black tumorous swellings from 1 to several inches in length, on limbs and twigs.
Control.—Burn all affected parts in the fall. Burn whole tree if badly affected.
Brown-rot.—See under Peach.

Polygonum. Tar-spot (Rhytisma bistortae).—Black tar-like spots on leaves.
Control.—Burn affected leaves.

Pomegranate. Internal Rot (Sterigmatocystis castanea).—Central cavity of fruit occupied by a black sporulating fungus.
Control.—None known.

Pomelo. Wither-tip (Colletotrichum gloeosporioides).—Anthracnose cankers of stem, spots on leaves and flowers and general wilting of tips of branches.
Control.—-Prune off affected parts and spray with bordeaux mixture.

Populus. Heart-rot (Polyporus sulphureus).—Red rot of the wood, which finally breaks up into cubes.
Control.—Surgery methods.

Potato. Early Blight (Alternaria solani).—-Circular spots, usually in July and final blighting of whole leaf.
Control.—Spray with Bordeaux mixture, every ten days, beginning when plants are 6 to 8 inches high. Late Blight and Potato-Rot (Phytophthora infestans).— Quick-spreading watery appearing spots in leaves.
Mildew on under side. Plants appear as scalded by hot water. Tubers rot in soil or soon after digging.
Control.-Spray with bordeaux mixture, 5-5-50, at least three applications and in wet seasons, six or more may be necessary. Use from forty to one hundred gallons per acre.
Scab (Oospora scabies).—A scabby and pitted roughness of the tubers.
Control.—Keep lime and ashes off the land. Soak uncut seed tubers in a solution of formalin, one pint to thirty gallons of water for two hours. Avoid land that has grown scabby potatoes.

Potentilla, Leaf-spot.—See under Strawberry.

Primula. Rot (Botrytis sp.)—Similar to rot of Paeonia, which see.

Prune.—See under Plum.

Primus.—See under Cherry, Plum and Peach.

Pseudotsuga. Blight (Sclerotinia fuckeliana).—Gray mold of seedlings and younger shoots of older
trees in moist situations.
Control.—Spray with bordeaux mixture.

Psidium.—See under Guava.

Pyrus.—See under Apple and Pear.

Quince. Blight.—See under Pear.
Rust (Gymnosporangium globosum).—Orange rust of fruit.
Control.—Destroy red cedars in the neighborhood, also wild apples and hawthorns. Spray as for
Apple Scab.

Radish. White "Rust" or Mildew (Albugo candidus).—A whitish powdery growth on the leaves and petioles, often causing distortion.
Control.—Steam sterilize the soil before planting.
Club-root.—See under Cabbage.
Black-rot.—See under Cabbage.

Ranunculus. Mildew (Plasmopara pygmaea).—Downy mildew of leaves.
Control.—Spray with bordeaux mixture.

Raspberry. Anthracnose (Gloeosporium venctum).—Circular or elliptical, gray scab-like spots on the canes.
Control.—Remove diseased canes as soon as fruit is picked. Avoid taking young plants from diseased plantings.
Crown-gall.—See under Blackberry.

Red, or Orange Rust (Gymnoconia interstitialis).—Dense red powdery growth on under side of leaves of black varieties and blackberries.
Control.—Dig up and destroy affected plants. Leaf-spot.—See under Dewberry. Same disease.

Retinospora. Gall (Gymnosporangium sp.).—Swellings on limbs and twigs with red-brown pustules covering them.
Control.—Prune off affected parts and keep at a distance from species of Pomeae.

Rhamnus. Rust (Puccinia coronata).—Irregular yellow blotches, with yellow pustules on under side of leaf. Also on fruit and flowers.
Control.—Keep at a distance from "rusted" cereals and other grasses.

Rheum. Soft-rot.—See under Carrot.

Rhododendron. Galls (Exobasidium rhododendri).—Galls of the size of a pea or larger, at first pale green, then red and brownish covered with white bloom.
Control.—Leaves bearing galls should be removed and burned.

Rhubarb. Soft-rot.—See under Carrot.

Rhus. Canker and Twig Blight (Endothia parasitica).—See under Chestnut. Causes death of twigs.

Ribes.—See under Currant and Gooseberry.

Richardia. Soft-rot (Bacillus aroideae).—Soft rotting of corms (bulbs) and leaves.
Control.—Change soil every three or four years. Reject corms which show the disease.

Robinia. Heart-rot (Trametes robiniophila and Fomes rimosus). —Heart-wood converted into punk. Shelf-like bodies grow from wounds.
Control.—Surgery methods.

Rose. Mildew (Sphaerotheca pannosa).—A white powdery mildew on new growth.
Control.—In greenhouses, keep steam-pipes painted with a paste of equal parts lime and sulfur mixed in water. Out-of- doors roses should be dusted with sulfur flower or sprayed with potassium sulfid, one ounce to three gallons of water. Stem-blight.—Similar to Raspberry Anthracnose, which see.

Rubus.—See under Raspberry.

Salix. Rust.—Numerous species of the rust fungi produce red rust spots on the leaves.
Control.—-Keep at a distance from species of conifers.
Heart-rot (Trametea suaveolens).—Enters through wounds.
Control.—Surgery methods.

Salsify. Mildew ( Albugo trogopogonis). — Distortion and white blisters on host.
Control.—Eradicate affected plants and grow on new soil apart from wild and cultivated species of the Composite.

Sambucus. Cankers.—See under Lonicera.

Sarracenia. Blight.—See under Orchids.

Saxifraga. Rust (Puccinia pazschkei and P. saxifrage}.—Dark brown concentric circles of rust pustules on upper surface of the leaves.
Control.—Burn affected leaves.

Scilla. Bulb-rot (Sclerotinia bulborum).—Yellow stripes and blotches on leaves in early summer, with olive-brown mold on them. Rots the bulb later.
Control.—Destroy affected plants. Spray with potassium sulfid. Use new soil thereafter.

Sedum. Leaf-spot (Septoria sedi),—Dark circular blotches appear on the leaves and defoliation occurs.
Control.—Destroy affected parts by burning.

Sempervivum. Rust (Endophyllum sempervivi).—Brown rust pustules rupturing epidermis of leaf.
Control.—Destroy affected plants as the fungus lives over from year to year in the some plant.

Senecio. Rust (Coleosporium senecionis).—Orange patches on under surface of leaf.
Control.—Keep at a distance from species of Pinus. Burn affected plants to protect neighboring pines.

Sequoia. Blight.—See under Pseudotsuga.

Silene. Smut.—-See under Lychnis.

Solanum.—See under Potato, Eggplant, etc.

Sorbus. Blight.—See under Pear.

Spinach. Anthracnose (Colletotrichum spinaceae).—Spots on leaves, at first minute and watery, gradually increasing in size and becoming gray and dry.
Control.—Gather and destroy all diseased leaves. Mildew (Peronospora effusa).—Gray, slightly violet, patches of a velvety texture on under side of leaves.
Control.—As for Anthracnose, which see.

Spiraea. Rust (Triphragmium ulmariae).—Reddish yellow and dark brown rust pustules on leaves.
Control.—Burn affected parts.

Squash. Wilt.—See under Cucurbita.

Strawberry. Leaf-spot, or Leaf-blight (Mycosphaerella fragariae).—Small purple or red spots appearing on leaves. Leaf appears blotched.
Control.—Spray with bordeaux mixture, 4-4-50, soon after growth begins and make three or four additional sprayings during season.

Sweet Pea. Mildew.—See under Pea.

Sweet Potato. Black-rot (Ceratocystis fimbriata),—Black shank and a black rot of tuber.
Control.—Never use sprouts from affected potatoes. Steam sterilize hotbeds.
Rots.—The sweet potato is susceptible to a large number of rots, soft, dry, hard, white, etc.
Control.—Use soil which has not grown diseased sweet potatoes heretofore.

Syringa. Mildew (Microsphaera alni).—White powdery mildew on upper surface of leaves.
Control.—Dust with sulfur.
Twig and Bud Disease (Phytophthora syringae).—Tips of twigs killed.
Control.—Prune off twigs.

Thalictrum. Red-spot (Synchytrium anemones).—Red eruptions on stem, leaf and flower. Causing at times swelling and crumpling of the organ.
Control.—Burn affected parts.

Thuja. Root-rot (Polyporus schweinitzii).—Diseased wood yellowish, cheesy, brittle when dry.
Heart-rot (Fomes carneus).—Causes pockets in the affected wood.
Control.—Remove all affected wood, using surgery methods.

Tilia. Leaf-spot (Cercospora microsora).—Causes spotting and defoliation.
Control.—Two sprayings in Massachusetts resulted in longer retention of the leaves.

Tomato. Leaf-spot (Septoria lycopersica}.—At first small spots appear, which spread until the whole leaf is consumed. Fruit may be attacked.
Control.—Spray with bordeaux mixture, 4-4-50, making the first application two weeks after the plants are set out and repeating every two weeks throughout the season.
Downy Mildew.—See under Potato. Late Blight.
End-rot.—Due to lack of sufficient soil moisture.
Control.—Water soil in dry periods.

Toxylon (Maclura). Rust (Physopella fici).—Pale cinnamon- brown rust pustules on under side of
leaf.
Control.—Destroy by burning the affected leaves.

TropaeoIum.—See under Horse-Radish.

Tsuga. Heart-rot (Trametes pini).— Light brown decay pitted with small oblong cavities, which are white-lined. Sap-rot (Fomes pinicola).—Soft decay of sap-wood.
Control.—Surgery methods.

Tulipa. Mold (Sclerotinia parasitica}.—Olive-brown, velvety patches formed on leaves, stem, and flowers; also, later, small black lumps at base of stems.
Control.—Burn affected plants.

Turnip. Club-root.—See under Cabbage. Same disease.
Soft-rot.—See under Carrot. Same disease.

Ulmus. Tar-spot (Gnomonia ulmea).—Black spots on upper surface of leaves.
Control.—Burn old leaves in fall or winter.
Heart-rot (Pleurotus ulmarius).—Soft rotting of wood.
Control.—Surgery methods.

Vaccinium. Leaf-blister (Exobasidium vaccinii).—Large blisters on leaves, petioles and stems, of a red or purple color. White bloom beneath.
Control.—Remove and burn diseased parts.

Verbena. Mildew. (Erysiphe cichoracearum and others).—Powdery mildew growths on leaves.
Control.—Spray with any good fungicide or dust with powdered sulfur.

Veronica. Leaf-Spot (Septoria veronicae).—Well-defined spots on leaves.
Control.—Pick off and burn affected leaves.

Vinca. Leaf-spot (Sphaeropsis vincae).—Leaves disfigured by spots which occur on the stem at times as well.
Control.—Destroy diseased parts of plants.

Violet. Root-rot (Thielavia basicola).—Plants make poor growth; roots rotted off.
Control.—Start in steam-sterilized soil, and transfer to sterilized beds.

Vitis.—See under Grape.

Walnut. Blight (Pseudomonas juglandis).—Black spotting of fruit and black cankers on the stems. Twigs and fruit-spurs lulled.
Control.—None known except such as mentioned under Pear Blight. Grow immune varieties. Anthracnose, or Leaf-blight (Marsonia juglandis).—See under Hickory-Nut. Same disease.

Watermelon. Mildew.-See under Cucumber.

Wilt (Fusarium vasinfecta). — Wilting of leaves and plant dries up.
Control.—None recommended. Resistant varieties should be grown.

Yucca. Leaf-blotch.—See under Agave.

Zea.—See under Corn.

Zinnia. Wilt.—See under Dahlia.
Donald Reddick.

Insect enemies of plants.

The animals which constitute the insect world play an important part in most horticultural operations. The busy bee is an indispensable aid in the production of many fruits, but the equally busy jaws of canker-worms or other insects oftentimes seriously interfere with man's plans for profitable crops. Horticulturists should become more intimately acquainted with their little friends and foes in the insect world. Not only from the economic standpoint is this knowledge necessary in the business of growing plants, but the striking peculiarities of form, coloring, structure, habits, and the wonderful transformations of insects afford one of the most interesting fields in nature. The life-stories of many insects, if told in detail, would rival in variety and interest many a famous fairy tale. The science that treats of insects, or entomology, has now reached the stage at which its devotees are no longer looked upon with ridicule in most communities. At the present time more than 350 trained men are officially employed in entomological work in the United States and Canada.

What they are.—An insect is an animal which, in the adult stage, has its body divided into three distinct regions: the head, the thorax and the abdomen (Fig. 1293). The head bears one pair of antennae, and there are always three pairs of legs and usually either one or two pairs of wings attached to the thorax. By these characteristics one can usually readily distinguish an adult insect from any other animal. Among the near relatives of insects in the animal world are the cray-fish, sow-bugs, and crabs, but these are mostly aquatic animals, breathing by true gills; they have two pairs of antennae, and at least five pairs of legs. Centipedes, or "hundred-legged worms," and millipedes, or "thousand-legged worms," are also nearly related to insects, but they have the thorax and abdomen forming a continuous region, and with six to 200 segments, each bearing one or two pairs of legs; they have one pair of antennae. The layman usually classes such animals as the spiders, mites and daddy - long - legs among the insects, but they form a distinct class, as they have the head and thorax grown together, no antennae, and have four pairs of legs.

How they are constructed.—Insects are constructed on an entirely different plan from the higher animals. Their supporting skeleton is outside, it being simply the skin hardened more or less by a horny substance, known as chitin. This firm outer wall, or skeleton, supports and protects the muscles, blood-vessels, nerves, and other organs within. The mouth-parts, antennae and eyes of an insect are attached to its head, and all are exceedingly useful organs, as will be shown later in discussing the feeling and the other sensations of an insect. An insect's wings and legs are always borne by the thorax. The wings are primarily organs of flight, but are used as musical organs by some of the grasshoppers and crickets. Female canker-worm moths, bed-bugs, and some other insects have practically no wings, and the house-flies, mosquitos, male bark lice, and similar insects have but one pair of wings. Insects use their legs primarily for locomotion; some have their front legs modified for catching other insects for food; others have hind legs fitted for jumping, while the honey-bee has little "pockets" on its hind legs for carrying pollen to feed its young.

The arrangement of the internal organs in insects is interesting and somewhat peculiar. The alimentary or food canal in larvae is a nearly straight tube, occupying the central portion of the body; in adult insects it is usually much longer than the body and is more or less folded; from the mouth the food passes through a pharynx, an esophagus, sometimes a crop and a gizzard, a stomach, and a small and large intestine. The nervous system of an insect is similar to that in the higher animals, but it extends along the venter instead of the back. There is a little brain in the upper part of the head, and two nerve cords extend from this around the food-canal to another ganglion or nerve center in the lower part of the head; two nerve cords then extend longitudinally along the venter and connect a series of nerve centers or ganglia, typically one for each segment of the body. From each of these ganglia or little brains nerves arise, which supply the adjacent organs and ramify throughout the body. In insects, all parts of the body cavity that are not occupied by the internal organs are filled with a rich, colorless or slightly greenish blood. There is no system of tubes like our arteries and veins, in which the blood is confined and through which it flows. There is a so-called "heart" above the food-canal, along the middle line of the back; it is a tube consisting of several chambers communicating with each other and with the body cavity by valvular openings. The blood is forced through this heart into the head, where it escapes into the body cavity. It then flows to all parts of the body, even out into the appendages, in regular streams which have definite directions, but which are not confined in tubes. They, like the ocean currents, are definite streams with liquid shores. Insects do not breathe through the mouth, as many suppose, but through a series of holes along the sides of the body. These openings, or spiracles, lead into a system of air- tubes, called tracheae. These trachea; branch and finally ramify all through the insect. Insects have no lungs, but the tracheae sometimes connect with air-sacs or bladders in the body, which help to buoy up the insect when flying. Thus the relation between the circulation of the blood and respiration is not nearly so intimate in insects as in man. In insects the air is carried to all the tissues of the body in the tracheae and the blood simply bathes these tissues. Just how the blood is purified and how the waste matter is disposed of in insects are not yet clearly understood. Aquatic insects breathe by either carrying down bubbles of air from the surface entangled under their wings, or they may be provided with organs known as tracheal gills; these are usually plate-like expansions of the body that are abundantly supplied with tracheae, in which the air is brought practically in contact with the air in water, and may thus be purified. More than 4,000 different muscles have been found in a single caterpillar. Notwithstanding their delicate appearance, these muscles are really very strong and their rapidity of action is wonderful; in certain gnats the muscles move or vibrate the wings 15,000 times a second.

Their sensations.—Insects can see, feel, hear, taste and smell, and they may also possess other senses, as a sense of direction. Many insects have two kinds of eyes. On each side of the head the large compound eye is easily recognized (Fig. 1294); each compound eye is composed of many small eyes, from fifty in some ants to many thousands in a butterfly or dragon-fly. Between these compound eyes, from one to four simple eyes are to be found in many adult insects. Caterpillars and other larvae possess only simple eyes. It is thought that each facet of the compound eye sees a part of an object; thus the whole eye would form a mosaic picture on the insect's brain. The simple eyes doubtless see as our eyes do, and seem to be best adapted for use in dark places and for near vision. Insects do not see the form of objects distinctly, but their eyes are doubtless superior to ours in distinguishing the smallest movements of an object. It is now supposed that no insects can distinctly see objects at a greater distance than 6 feet. It must be a sixth sense, a sense of direction, which enables the bee to find its way for a mile or more back to its home. Insects are doubtless able to distinguish the color of objects, and some insects seem to prefer certain colors. Blue is said to be the favorite color of the honey-bee, and violet that of ants; ante are also apparently sensitive to the ultra-violet rays of light, which man cannot perceive. It is generally supposed that the shape and high colors of flowers attract insects; but recent experiments seem to show that insects are guided to flowers by the sense of smell rather than by sight. The hard outer skin of an insect has no nerves distributed in it, hence it is not sensitive; but it is pierced with holes, in which grow hairs that are in connection with nerves at their base. It is by means of these sensory hairs that insects feel, and are sensitive to touch on most parts of the body. Doubtless insects are not deaf, for we know that many of them make sounds, and it must naturally follow that they have ears to hear, for there is every reason to suppose that they make these sounds as love-songs to attract the sexes, as a means of communication, or possibly to express their emotions. Some think that bees and ants hear sounds too shrill for our ears. Insects have no true voice, but produce various noises mechanically, either by rapid movements of their wings, which causes the humming of bees and flies, of by friction between roughened surfaces on the body or its appendages, thus producing the rasping sounds or shrill cries of some crickets and grasshoppers. The house-fly hums on F, thus vibrating its wings 335 times in a second, while the wing tone of the honey-bee is A. Usually the males are the musicians of the insect world, but it is the female of the familiar mosquito which does the singing, and the "biting" also. The male mosquito doubtless hears the song of his mate by means of his antenna, as the song causes the antennal hairs to vibrate rapidly. Organs which are structurally ear- like have been found in various parts of the body of insects. The common brown grasshoppers of the fields have a large ear on each side of the first segment of the abdomen; one can easily distinguish with the naked eye the membrane or tympanum stretched over a cavity. Many of the long-horned green grasshoppers, katydids and crickets have two similar ears on the tibia of each front leg. Some think that mosquitos have the faculty of the perception of the direction of sound more highly developed than in any other class of animals. Insects undoubtedly possess the sense of taste. When morphine or strychnine was mixed with honey, ants perceived the fraud the moment they began to feed. The substitution of alum for sugar was soon detected by wasps. Bees and wasps seem to have a more delicate gustatory sense than flies. Taste organs have been found in many insects, and are usually situated either in the mouth or on the organs immediately surrounding it. Many experiments have shown that the antennae are the principal organs of smell in insects. Blow-flies and cockroaches which have had their antennae removed are not attracted by their favorite food, and male insects find their mates with difficulty when deprived of their antennae. The familiar world which surrounds us may be a totally different place to insects. To them it may be full of music which we cannot hear, of color which we cannot see, of sensations which we cannot perceive. Do insects think or reason? Why not? Their actions are said to be the result of inherited habit or instinct. But some of them have been seen to do things which require the exercise of instinctive powers so acute and so closely akin to reason that one can hardly escape the conclusion that some insects are endowed with reasoning powers.

Their number, size and age.—Experts guess that there are from 2,000,000 to 10,000,000 different kinds of insects in the world. Only about 400,000 of these have yet been described and named by man. Between 30,000 and 40,000 are now known in North America. Four-fifths of all the kinds of animals are insects; some single families of insects are said to contain more species than one can see stars in a clear sky at night; and there are as many butterflies as birds in North America. The larger part of the land animals are insects, and it is asserted that the larger proportion of the animal matter existing on the lands of the globe is probably locked up in the forms of insects. Insects vary in size from little beetles, of which it would take 100, placed end to end, to measure an inch, up to tropical species 6 or 8 inches in length, or of equal bulk to a mouse. Insects have a very long, but, as yet, very imperfect pedigree extending through the geological ages to Silurian times. Fossil remains of many different kinds of insects have been found in the rocks (Fig. 1295); even such delicate insects as plant- lice left their impress on the rocks ages ago. In the carboniferous or coal age, the insect world was evidently quite different from that of today, for fossils of veritable insect mammoths have been found; dragon-flies with a wing-expanse of 2 to 3 feet then existed. Insect fossils found in the tertiary rocks indicate that there were even more kinds of insects then than now.

Their growth and transformations. Fig. 1296.—Insects begin life as an passed as an egg; in some cases the egg stage is passed within the body of the mother, which then gives birth to living young. The eggs of insects exhibit a wonderful variety of forms, sizes, colors and characteristic markings. A single scale insect may lay thousands of eggs, while some plant-lice produce only one. Remarkable instinct is often shown by the mother insect in placing her eggs where her young will find proper .food. From their birth the young of some of the lowest or most generalized insects closely resemble their parents, and they undergo no striking change during their life; hence are said to have no metamorphosis. In the case of grasshoppers, stink- bugs, dragon-flies, and many other insects, the young at birth resemble their parents, but have no wings. As they grow, wings gradually develop and often changes in markings occur, until the adult stage is reached. The growth, however, is gradual, and no striking or complete change occurs, and these insects are said to undergo an incomplete metamorphosis. The young insects in all stages are called nymphs (Fig. 1297); thus insects with an incomplete metamorphosis pass through three different forms during their life: an egg, the young or nymph stage, and the adult. From the eggs of butterflies, moths, flies, beetles, bees and some other insects, there hatches a worm-like creature, much unlike the parent insect. It is called a larva (Fig. 1298); the larvae of butterflies and moths are often called caterpillars (Fig. 1299); maggots are the larvae of flies (Fig. 1300); and the term grub is applied to the larvae of beetles and bees (Fig. 1301). When these larvae get their full growth, some of them go into the ground where they form an earthen cell, while others proceed to spin around themselves a silken home or cocoon (Figs. 1302- 1304). In these retreats the larvae change to a quiescent or lifeless-appearing creature which has little resemblance to either the larva or the parent insect. It is call a pupa (Fig. 1305). The pupae of butterflies are often called chrysalids. Flies change to pupae in the hardened skin of the maggot. Some pupae, like those of mosquitos, are very active. Wonderful changes take place within the skin of the pupa. Nearly all the larval tissues break down and the insect is practically made over, from a crawling larva to a beautiful, flying adult insect. When the adult is fully formed, it breaks its pupal shroud and emerges to spend a comparatively brief existence as a winged creature. Such insects are said to undergo a complete metamorphosis, and pass through four strikingly different stages during their life: the egg, the worm- like larva, the quiescent pupa, and the adult insect. Such remarkable changes or transformations make the story of an insect's life one of intense interest to one who reads it from nature's book. Various kinds of adult insects, or imagoes, are shown in Figs. 1306-1311. No two kinds of insects have the same life-story to tell. Some pass their whole life on a single host; some partake of only a certain kind of food, while others thrive on many kinds of plants; some are cannibals at times, and others, like the parasites, are boarders within their host, while many prey openly on their brethren in the insect world. Usually the life of the adult insect is brief, but ants have been kept for thirteen years, and the periodical cicada has to spend seventeen years as a nymph Underground before it is fitted to become a denizen of the air. The winter months may be passed in any of the different stages of the insect's life. Two very closely allied insects may have very different life habits.

How they grow.—Many persons think that the small house-flies grow to be the large ones. While most insects feed after they become adults, they get little or none of their growth during their adult life. Insects grow mostly while they are larvae, or nymphs. The maggots from which the little house-flies develop doubtless do not have as luxuriant or favorable feeding-grounds as do those of the larger flies. In thirty days some leaf-feeding caterpillars will increase in size 10,000 times; and a certain flesh-feeding maggot will in twenty-four hours consume two hundred times its own weight, which would be paralleled in the human race if a one- day-old baby ate 1,500 pounds the first day of its existence! The skin of insects is so hard und inelastic that it cannot stretch to accommodate such rapid growth. But nature obviates this difficulty by teaching these creatures how to grow a new suit of clothes or a new skin underneath the old one, and then to shed or molt the latter. The old skin is shed in its entirety, even from all the appendages, and sometimes remains in such a natural position where the insect left it as to easily deceive one into thinking that he is looking at the insect rather than at its cast-off clothes. Some insects are so neat and economical that they devour their old suits or skins soon after molting them. Larvae, or nymphs, may molt from two or three to ten or more times; the larvae do not often change strikingly in appearance, but the nymphs gradually acquire the characters and structures of the adult.

How they eat.—To the horticulturist, the mouth- parts of an insect are its most important organs or appendages. The mouth-parts are built on two very different plans. Grasshoppers, beetles, caterpillars and grubs have two pairs of horny jaws, working from side to side, with which they bite or chew off pieces of their food, that then pass into the food- canal for digestion (Fig. 1312). The scale insects (Fig. 1313), plant-lice, true bugs (Fig. 1314), mosquitos and others have these jaws drawn out into thread-like organs, which are worked along a groove in a stiff beak or extended under-lip. Such insects can eat only liquid food, which they suck with their beak-like mouth-parts. The insect places its beak on the surface of the plant, forces the thread-like jaws into the tissues, and then begins a sucking operation, which draws the juices of the plant up along the jaws, and the groove in the beak into the food-canal of the insect. Thus a sucking insect could not partake of particles of poison sprayed on the surface of a plant. Its mouth-parts are not built for such feeding, and as it is impracticable to poison the juice of the plant, one is forced to fight such insects with a deadly gas, or each individual insect must be actually hit with some insecticide. A knowledge of these fundamental facts about the eating habits of insects would have saved much time and money that have been wasted in trying to check the ravages of sucking insects with paris green and similar poisons. Some insects, like the fruit flies, have mouth-parts fitted for lapping up liquids.

Beneficial insects.

The horticulturist has many staunch and true friends among the insects. The honey-bee, the many wild bees, and other insects, as they visit the blossoms to get food for themselves, for their young, and honey for man, leave an insurance policy in the shape of tiny grains of pollen, which often insures a crop of fruit that otherwise might be extremely uncertain. The honey-bee is often accused of biting into ripe fruits, especially grapes. They have not yet been proved guilty, and careful, exhaustive experiments have shown that they will not do it under the most favorable circumstances. Wasps and other strong-jawed insects are responsible for most of this injury, the bees only sipping the juice from the wound. See Bees, Vol. I. Most of the pretty little beetles known to every child as "lady-bugs" eat nothing but injurious insects; many other beetles are also predaceous. Man is also often deeply indebted to many of the two-winged insects or true flies whose larvae live as parasites inside the body of insect pests or feed upon them predaceously. Were it not for the ravenous larvae of the "lady-bugs" and of the syrphus flies, plant-lice of all kinds would soon get beyond control. While man must recognize these little friends as valuable aids in his warfare against the hordes of insect pests, it will rarely be safe to wait for the pests to be controlled by their enemies. Fig. 1315 shows a tomato worm bearing the cocoons of a parasite. Fig. 1310 shows one of the predaceous beetles destroying a cutworm.

Injurious insects.

There are now several thousand different kinds of insects that may be classed as injurious in the United States and Canada. Over 600 kinds were exhibited at the Columbian Exposition in 1893. All of these may not be injurious every year, as most insect pests have periods of subsidence, when certain factors, possibly their enemies or perhaps climate conditions, hold them in check. The put- look for American horticulturists, so far as injurious insects are concerned, is not encouraging. Nowhere else in the world are insects being fought as intelligently, successfully and scientifically as in America, yet we never have exterminated, and it is very doubtful if we ever will, a single insect pest. This means that American horticulturists will never have any fewer kinds of insects to fight. On the contrary, there are many more insect pests now than in our grandfather's early days, and new pests are appearing every year. This alarming state of affairs is largely due to two causes, for both of which man is responsible. Man is continually encroaching upon and thereby disturbing nature's primitive domain and the equilibrium which has there become established between animals and plants. In consequence, insects like the Colorado potato beetle, the apple-tree or the peach- tree borers have been attracted from their original wild food-plants to man's cultivated crops, which often offer practically unlimited feeding-grounds. Most of the new insect pests, however, are now coming to America from foreign shores. American horticulturists are continually importing plants from the ends of the earth, and oftentimes the plants are accompanied by one or more of their insect pests. Some comparatively recent introductions of this kind are the sinuate pear- borer, the pear midge, the gypsy moth, the brown-tail moth, the horn-fly and the elm leaf-beetle; such standard pests as the Hessian fly, the cabbage butterfly, the currant-worm, the codlin-moth (Fig. 1296) came in many years ago. Of the seventy-three insects which rank as first-class pests, each of them almost annually causing a loss of hundreds of thousands of dollars, over one-half have been introduced from foreign countries, mostly from Europe. It is a significant fact that usually these imported insects become much more serious pests here than in their native home; this is doubtless largely due to the absence of their native enemies, to more favorable climatic conditions here, and to a less intense system of agriculture in this country. Most of our worst insect pests of the fruits, of the garden crops, of the granary, of the household, of the greenhouse, and practically all of our most dangerous scale insects, are of foreign origin. Man will continue to encroach on and disturb nature's primitive domain, and commercial operations will never cease, nor is there much hope of ever effectually quarantining our shores against these little foes; hence there seems to be no practicable way to stop this increase of the insect enemies of the horticulturist. The one who is the best fitted by nature, and who best fits himself with a knowledge of these pests and how to fight them, will usually be the one to survive and reap the reward of profitable crops. No part of a plant, from its roots to the fruit it produces, escapes the tiny jaws or the sucking beaks of insects.

Root-feeding insects. —Many of the small fruits and vegetables are often seriously injured by insects feeding on the roots. The grape-vine fidia (the grub of a small beetle) and the grape phylloxera plant-louse live on grape roots. Strawberries often succumb to the attacks of the grubs of several small beetles known as strawberry-root worms, and to the large white grubs of the May beetles. The roots of cabbages, radishes and other cruciferous plants are often devoured by hordes of hungry maggots. These underground root-feeding insects are difficult pests to control, like any other unseen foe. Sometimes they can be reached successfully by injecting a little carbon bisulfide into the soil around the base of the plant. The cabbage maggots can be prevented largely by the use of tarred paper pads placed around the plants, or by pouring a carbolic acid emulsion at the base of the infested plants. The strawberry root-feeders are best controlled y frequent cultivation and a short rotation of crops.

Borers.—These are the larvae of several different kinds of insects, which burrow into and feed upon the inner bark, the solid wood, or the interior pith of the larger roots, trunks, branches, and stems or stalks of many horticultural plants. Nearly every kind of fruit trees is attacked by its special kind of borer, as are also many of the smaller vine and bush-fruits and garden crops. Borers are often the most destructive of insect pests. The two apple-tree borers, the round- headed (Fig. 1316) and the flat-headed species, and the peach-tree borer (Fig. 1311) doubtless cause the death of as many apple and peach trees in America as all other enemies combined. The fruit-bark beetles, or "shot-hole" borers, usually attack only unthrifty or sickly fruit trees, and a tree once infested by them is usually doomed. Two borers, one the grub of a beetle and the other the caterpillar of a moth, sometimes tunnel down the stems of currants and gooseberries. Raspberries and blackberries (Fig. 1317) also suffer from two or thee kinds of borers, one working in the root, one in the stem, and a maggot bores down and kills the new shoots. A caterpillar closely allied to the peach- tree borer lives in squash vines, often ruining the crop. The potato-stalk weevil sometimes does much damage in potato fields. Sometimes one can prevent borers from getting into a fruit tree with a paper bandage closely wrapped around the part liable to be attacked, or by the application of some "wash." Most of the washes recommended will prove ineffectual or dangerous to use. Gas-tar has given good results, but some report injury to peach trees from its use; Hence one should first experiment with it on a few trees. No way has been found to keep borers out of the small fruits or garden crops; usually if infested canes, stems or plants are cut out and burned early in the fall or whenever noticed, most of the borers will be killed. When borers once get into fruit trees, the "digging-out" process is usually the only resort, although some report that they readily kill the depredator by simply injecting a little carbon bisulfide into the entrance of his burrow and quickly closing it with putty.

Bud- and leaf-feeding insects.— The buds and leaves of horticultural crops often swarm with legions of biting and sucking insects. A mere enumeration of the different kinds of these pests would weary the reader. Some insects, like the rose chafer, work on several different kinds of plants, while many others attack only one or two kinds. In apple orchards, the opening buds are seized upon by the the hungry bud-moth and case-bearing caterpillars, by the newly hatched canker-worms, and by tent-caterpillars, whose tents or "sign-boards" are familiar objects in many orchards. These pests continue their destructive work on the leaves. The pear slug often needs to be checked in its work of skeletonizing the leaves of the pear and cherry. The pear psylla, one of the jumping plant- lice, is a very serious menace to pear-growing in many localities; the fruit is either dwarfed or drops from badly infested trees, and sometimes so many little pumps sucking out its life finally cause the death of the tree. The little blue grapevine flea-beetle often literally nips the prospective crop of fruit in the bud, or the rose-chafer may swarm over the vines and eat the foliage or blossoms. Currant gooseberry growers realize that eternal vigilance against the familiar green currant worms is the price of a crop of fruit. The asparagus beetles would soon appropriate every asparagus shoot that appears in many localities. It is a continual struggle against insect pests to get a paying crop of almost any vegetable. The several kinds of cabbage caterpillars would soon riddle the leaves. The hungry striped cucumber beetles can hardly wait for the melon, squash, or cucumber vines to come up. Two sucking insects, the harlequin cabbage bug and the squash stink-bug, are equally as destructive as their biting relatives. The bud- and leaf-feeding insects are usually readily controlled by spraying some poison on their food, or by hitting them with some oil or soap spray. As the female moths of canker-worms are wingless, a wire trap or sticky bandage placed around the trunk of the tree in the late fall and early spring, to capture the moths as they crawl up the tree to lay their eggs, will greatly help to check these serious pests. The collection and burning of the conspicuous egg-rings of the tent-caterpillars at any time between August and the following April will greatly reduce the vast numbers of tents or signboards of shiftlessness in apple orchards. Hand - picking or collecting is the most successful method of controlling the rose-chaufer, harlequin cabbage bug and the squash stink-bug in many cases. Prompt action, guided by a knowledge of the insect's habits and life- history, and any intelligent use of materials and apparatus, are essential in any successful effort to control these bud- and leaf-feeding pests of the horticulturist.

Fruit-eating insects.—"Wormy" apples, pears, quinces, plums, peaches, cherries, apricots, grapes, currants and nuts are often the rule rather than the exception. The codlin-moth or apple-worm often ruins from one-third to one-half of the crop each year in many localities; it also infests pears seriously. The apple maggot tunnels its way through and through the flesh of a large percentage of the apples in the northern sections of the country. Most of the wormy plums, peaches, cherries and apricots are the work of the grub of that worst insect enemy of the stone fruits—the plum curculio; the plum gouger, a similar insect, whose grub works in the pit of plums, is equally destructive to this fruit in some states. "Knotty" quinces are largely the work of the adults of the quince curculio, while its grub often ruins the fruit with its disgusting worm-hole. There is also a grape curculio that, with the aid of the caterpillar of a little moth, works havoc in grapes. Currants and gooseberries are often wormy from the work of two or three different kinds of maggots and caterpillars. Two kinds of fruit flies attack the cherry; infested cherries may show no external signs of the presence of the maggot reveling in the juices within. Various small beetles known as weevils, are responsible for most wormy nuts. Most of the fruit-eating insects are out of the reach of the ordinary insecticides. The codlin-moth is a noted exception, however, for the peculiar habit that the little caterpillar has of usually entering the blossom end of the fruit and feeding therein for a few days, gives the man with a poison spray a very vulnerable point of attack. It is only necessary to spray a bit of poison into the open calyx cup within a few days after the petals fall, and let nature soon close the calicos and keep the poison therein until the newly-hatched caterpillar includes it in its first menu. Often 95 per cent of the apples that would otherwise be ruined by the worms are saved by an application of paris green at this critical time.

Plant-lice.—Scarcely a plant escapes the little suction pump or beak of some kind of a plant-louse or aphis. More than 300 different kinds of plant-lice have been identified in the United States, and nearly every kind of fruit, flower, farm or garden crop has its special plant-louse enemy, which is often a serious factor in the production of a crop. These little creatures are so small, so variable, so hard to perceive, present so many different forms in the same species, and have such varied and interesting life-stories to tell, that what is known about them is but a mere beginning as compared to what is yet to be learned. It would take a large volume to include the interesting stories which might be told of the lives and of the relations with ants of some of the commonest of these plant-lice. No other group of insects presents so many curious, varied, interesting, and wonderful problems of life as do the aphids. In the aggregate, the damage done by plant-lice is very great. At times hundreds of acres of peas have been ruined by on aphid. Nursery stock often suffers severely and bearing fruit trees are often seriously injured by them. About forty different kinds of aphides live in greenhouses where a perpetual warfare has to be waged against them. In four years nearly 100 generations of a common aphis have been reared in greenhouses, and there were no indications of any egg-stage or of male forms during this time, so that they may thus breed indefinitely in houses, their young being born alive and no males appearing. The standard remedies for plant-lice are whale-oil soap, kerosene emulsion, and tobacco in various ways (as a decoction, dry as a dust, or in the form of similar extracts), and these are successfully used to kill the aphides in all situations.

Scale insects.—Since the advent of San Jose1 scale into the eastern United States; scale insects of all kinds have attracted world-wide attention. They are all small insects, and derive their name from the fact that their tender bodies are protected by hard, scale-like coverings secreted by the insects. Thus protected, they are difficult insects to kill, and as they are easily transported on nursery stock, buds or cions, and also multiply rapidly, the scale insects are justly to be considered as among the most dangerous and destructive of injurious insects. A single female San Jose scale may rear a brood of from 100 to 600 young, and there may be four or five generations a year; and more than 2,000 eggs have been laid by a single Lecanium scale. The scale insects, the dreaded San Jose species included, can be controlled successfully by judicious, intelligent and timely work with sprays of lime-sulfur, crude petroleum, or hydrocyanic acid gas, which should be used in the case of nursery stock. Since 1889 fumigation with hydrocyanic acid gas has been extensively practised in the citrus orchards of California, and now Florida and South African fruit-growers are also using it in their orchards. Large gas-tight tents or boxes are placed over the trees and the gas then generated within. Much nursery stock is now treated with the gas in tight boxes or houses; this is required by law in many states, and it should be practised in other regions. Recently greenhouses, railway coaches, rooms in private houses, and whole flouring mills have been effectively fumigated with this gas.

Insects are preserved in collections by securing them in tight cases by means of a pin inserted through the thorax, or through the right wing if the subject is a beetle. Moths and butterflies are pinned in position on a spreading-board until thoroughly dried. See Figs. 1318-1322. Every horticulturist should make a collection of injurious insects.

Insect literature for horticulturists.—Horticulturists should keep in close touch with the experiment stations and state entomologists of their own and of other states, and also with the Department of Agriculture at Washington; for it is from these sources that the best and latest advice regarding injurious insects is now being disseminated free, either by personal correspondence or by means of bulletins. Among the books, one or more of which may well find a place in a horticulturist's library are the following: Weed's "Insects and Insecticides," Lodeman's "The Spraying of Plants," Saunders' "Insects Injurious to Fruite," Sanderson's "Insect Pests of Orchard, Farm and Garden," and Slingerland and Crosby's "Fruit Insects." M. V. Slingerland. C. R. Crosby

Other invertebrate animals.

Mites.—Mites belong to the class of animals known as Arachnida, which are closely related to insects. Spiders and scorpions also belong in this group. Mites are small creatures, usually possessing four pairs of legs when mature, and the body is not divided into three divisions as in the case of insects. The greenhouse red-spider (Tetranychus bimaculatus) is one of the most common and injurious species. It occurs on a wide variety of plants grown under glass and also out-of-doors on the foliage of many wild and cultivated plants. It is about 1/50 in. long and varies in color from yellow through orange to brown and dark green, often with a darker spot on each side of the body. It spins a very delicate silken web-like nest over its breeding- ground. It can be killed on the foliage of plants grown in the open with soap solution, dusting with sulfur, and hydrated lime, or by using a flour-paste spray. In greenhouses, it is best controlled by repeated spraying with water, using much force and little water to avoid drenching the beds.

The clover mite (Bryobia pratensis) is a minute, spider-like, oval, reddish brown mite about 3/100 inch in length with long front legs. It attacks the foliage of many fruit and forest trees as well as clover and grasses. The tiny, round, reddish eggs often occur in great numbers on the bark of trees in winter giving the branches a reddish color. It may be controlled by the same treatment as for red-spider. In addition, the eggs may be killed with a lime-sulfur solution while the trees are dormant.

The pear-leaf blister-mite (Eriophyes pyri) differs from most other mites in having only two pairs of legs and in its elongate body. The mite is only 1/125 inch in length; it burrows in the tissue of the leaf, causing blister-like galls. The eggs are laid within the gall, and some of the mites when mature leave through a small opening and migrate to new leaves. The mature mites hibernate under the bud-scales. This pest is controlled by applications of lime-sulfur or miscible oils while the trees are dormant.

Nematodes.—A species of nematode worm (Heterodera radicicola) lives parasitically in the roots of a wide variety of wild and cultivated plants producing enlarged knots or swellings. This disease is known as root-knot and is more prevalent in light soils. It is especially troublesome in greenhouses. The adult female worm is flask-shaped, .5 to 1 mm. in length, pearly white in color, and is found within the knots on the roots. Each female lays several hundred eggs. The young, worms may continue within the same root or migrate through the soil to others. Nematode root-galls have been found on nearly 500 different species of plants. It is especially destructive to okra, hollyhock, Amarantus tricolor, peach, snapdragon, celery, heart-leaved basil, wax gourd, beet, rape, red pepper, balloon vine, melon papaw, catalpa, endive, watermelon, coffee, muskmelon, cucumber, squash, pumpkin, carrot, deutzia, California poppy, fig, soybean, pecan, morning-glory, lettuce, gourd, sweet pea, flax, tomato, tobacco, peony, ginseng, passifiora, petunia, tuberose, cherry, pomegranate, eggplant, potato, salsify, clovers, violet, Old World grape. See page 1023.

This pest may be controlled in greenhouses by the use of live steam to sterilize the soil or by a weak solution of formaldehyde, one part, 36 to 40 per cent formaldehyde, to one hundred parts water, applied at the rate of one to one and one-half gallons to every square yard of soil surface of shallow beds. After the application, the soil should be thoroughly stirred and planting should not be done till at least ten days later. Under field conditions, the problem is more difficult. The most feasible method is a system of crop-rotation in which an immune crop is grown for at least two years between susceptible crops. One of the most resistant crops is the Iron variety of cowpea. Clean cultivation should be practised so as to destroy all susceptible plants.

Insecticides.

Insecticides are substances used to kill insects, as poisons, washes and gases. Insects are subject to many natural checks, such as wind, rains, sudden changes of temperature, the attacks of parasites and predaceous enemies, and are often destroyed in great numbers by bacterial and fungous diseases. In spite of these natural checks it is, however, usually necessary to resort to a spray or some other artificial insecticide for the protection of our crops.

The essential requirements for a satisfactory insecticide are: efficient killing power, safety to the foliage, cheapness and ease of application. The choice of an insecticide for any particular case will depend upon a number of factors: upon the structure, habits, and life-history of the insect to be killed; and upon the susceptibility of the host plant to injury, its mode of growth and the conditions under which it is cultivated. Some insects, as the plant-lice, are soft-bodied and provided with a thin and delicate integument; others, like the beetles and wireworms, have hard, horny shells impervious to ordinary spray liquids; some insects bite off and swallow portions of the plant, while others merely suck out the sap by means of a slender tube; some are injurious in the larval stage, others as adults; some attack the roots, some the foliage and fruit, while others burrow in the trunk and branches. Plants vary greatly in their susceptibility to injury from the use of insecticides; the peach and Japan plum have especially tender foliage, while the apple is not so easily injured. All these points and many more must be considered in selecting an insecticide which will be adapted to the control of any injurious insect. Our methods of fighting insects are constantly changing as new facts are discovered, new methods devised and new insecticides invented. Our present methods are the results of a more or less unconscious cooperation extending over many years between the practical grower, the student of insect life and the progressive manufacturers of spraying materials and spray machinery.

Insecticides may be classed into those which are eaten with the food and kill by poisoning; those that kill by contact with the insect's body; and fumes of gases used for fumigation. The poisons are effective against the biting or chewing and lapping (fruit flies) insects; the contact insecticides are used as a rule against sucking insects; and fumes and gases are employed principally in greenhouses and for the fumigation of nursery stock, stored seeds, and citrus trees.

Poisoning insecticides.

The most widely used substance for the poisoning of insects if arsenic in its various compounds. For this purpose only compounds insoluble in water can be used, as soluble arsenic is very injurious to foliage.

White arsenic.—This is the cheapest form in which arsenic can be obtained. It is a white powder, soluble in water and very injurious to foliage. A cheap and efficient insecticide may be prepared from it as follows:

For use with bordeaux mixture only. Sal-soda, two pounds; water, one gallon; arsenic, one pound. Mix the white arsenic into a paste and then add the sal-soda and water, and boil until dissolved. Add water to replace any that has boiled away, so that one gallon of stock solution is the result. Use one quart of this stock solution to fifty gallons of bordeaux mixture for fruit trees. Make sure that there is enough lime in the mixture to prevent the caustic action of the arsenic.

For use without bordeaux mixture. Sal-soda, one pound; water, one gallon; white arsenic, one pound; quicklime, two pounds. Dissolve the white arsenic with the water and sal-soda as above, and use this solution while hot to slake the two pounds of lime. Add enough water to make two gallons. Use two quarts of this stock solution in fifty gallons of water.

As there is always some danger of foliage injury from the use of these home-made arsenic compounds, and as they cannot be safely combined with the dilute lime-sulfur when used as a summer spray, they are now rarely employed in commercial orchard spraying. Paris green.—Paris green is composed of copper oxid, acetic acid and arsenious oxid chemically combined as copper-aceto- arsenite. By the National Insecticide Law of 1910, paris green must contain at least SO per cent arsenious oxid and must not contain arsenic in water-soluble form equivalent to more than 3 H per cent arsenious oxid. For many years paris green has been the standard insecticide for orchard use, but is now largely replaced by the safer and more adhesive arsenate of lead. In spraying apples, paris green is used at the rate of one-half pound to one hundred gallons of water or bordeaux mixture. When used with water, lime twice the bulk of the paris green should be added to lessen the danger of foliage injury. Paris green cannot safely be used with either the dilute lime-sulfur as used for summer spraying or with the self-boiled lime-sulfur.

London purple.—London purple is an arsenite of lime and is a by-product in the manufacture of aniline dyes. Its composition is variable, the arsenic content varying from 30 to 50 per cent. Owing to the presence of much soluble arsenic it is likely to cause foliage injury, and it is now little used in commercial spraying.

Arsenate of lead.—Arsenate of lead was first used as an insecticide in 1893, in Massachusetts. It is now almost entirely replaced by paris green for orchard work throughout the country. It adheres better to the leaves, may be used at considerably greater strength without injuring the foliage and may be combined with a dilute lime-sulfur solution or with the self-boiled lime-sulfur. Chemically, arsenate of lead may be either triplumbic arsenate or plumbic-hydrogen arsenate. The commercial product usually consists of a mixture of these two forms, the proportion depending on the method of manufacture employed. It is usually sold in the form of a thick paste, but for some purposes the powdered form is preferred. Under the National Insecticide Law of 1910, arsenate of lead paste must not contain more than 50 per cent water and must contain the arsenic equivalent of at least 12½ per cent arsenious oxid. The water-soluble arsenic must not exceed an equivalent of three-fourths of 1 per cent of arsenic oxid. In the best grades of arsenate of lead paste the chemical is in a finely divided condition, and thus when diluted for use remains in suspension for a considerable time. Arsenate of lead is used at various strengths, depending upon the insect to be killed and on the susceptibility of the foliage to injury. Four pounds in one hundred gallons can be used on the peach if combined with the self-boiled pine-sulfur; on apple, four or five pounds in one hundred gallons is usually sufficient; on grapes for lulling the grape root-worm beetles and the rose-chafer, eight to ten pounds in one hundred gallons have been found necessary. The poison is more readily eaten by these beetles if sweetened by two gallons of molasses in one hundred gallons, but, unfortunately, the addition of molasses greatly decreases the adhesiveness of the poison. Some species of fruit flies may be controlled by the use of sweetened arsenate of lead sprayed on the foliage of the plants at the first appearance of the flies. They lap up the poison with their fleshy tongue-like mouth-parts and succumb before ovipositing.

Arsenite of zinc.—Arsenite of zinc is a light fluffy powder and contains the equivalent of about 40 per cent arsenious oxid. It has been used extensively on the Pacific slope as a substitute for arsenate of lead. It kills somewhat more quickly and is fairly safe on apple foliage when used with bordeaux mixture or with lime. When sweetened with molasses, it is injurious to foliage. One pound of zinc arsenate is equivalent to about three pounds of arsenate of lead. In orchard experiment's, as a rule, it has not shown that it is superior to the latter.

Hellebore.—Hellebore is a light brown powder made from the roots of the white hellebore plant (Veratrum album), one of the lily family. It is applied both dry and in water. In the dry state, it is usually applied without dilution, although the addition of a little Sour will render it more adhesive. In water, four ounces of the poison is mixed with two or three gallons, and an ounce of glue, or thin flour paste, is sometimes added to make it adhere. A decoction is made by using boiling water in the same proportions. Hellebore soon loses its strength, and a fresh article should always be demanded. It is much less poisonous than the arsenicals, and should be used in place of them upon ripening fruit. It is used for various leaf-eating insects, particularly for the currant-worm and rose-slug.

Contact insecticides.

The most important contact insecticides are soaps, sulfur, sulfur compound, and oily or resinous emulsions.

Soaps.—The most commonly used soap solution is that prepared from fish-oil soap. The commercial brands of this soap are usually by-products and contain many impurities; further, many of them contain on excess of free or uncombined alkali and are thus likely to injure young and tender foliage. A good fish-oil soap may be prepared by the following formula: Caustic soda, six pounds; water, one-half gallon; fish-oil, twenty-two pounds. Dissolve the caustic soda in the water and then add the fish-oil gradually under constant and vigorous stirring. The combination occurs readily at ordinary summer temperatures, and boiling is unnecessary- Stir briskly for about twenty minutes after the last of the oil has been added. There is now on the market a good brand of insecticide soap prepared from cotton-seed oil soap stock or from an impure grade known as pancoline.

Sulfur.—Sulfur may be obtained in two forms,—flowers of sulfur and flour of sulfur. In the form of a powder or dust, sulfur is especially valuable against red-spider. In California, flowers of sulfur mixed with equal parts of hydrated lime is blown on the trees for the control of red-spider and mite. It may also be used for the same purpose mixed with water at the rate of one pound in three gallons of water, to which has been added a little soap to keep the sulfur in suspension. The mixture should be agitated constantly during spraying. The sulfur remains longer in suspension if it is first made into a paste with water containing one-half of 1 per cent of glue. Page 1028.

Lime-sulfur solution.—A solution of lime-sulfur was first used as an insecticide in California in 1886. It is now the standard remedy for blister mite, San Jose scale and similar scales, as well as an efficient fungicide. The lime-sulfur solution may be purchased in the concentrated form or may be prepared as follows: Lump lime (95 per cent calcium oxid), thirty-eight pounds; lump lime (90 per cent calcium oxid), forty pounds; sulfur, eighty pounds; water, fifty gallons. Make a paste of the sulfur with about ten gallons of hot water. Add the lime. As the lime slakes, odd hot water as necessary to prevent caking. When the lime has slaked, odd hot water to make fifty gallons and boil one hour, stirring constantly. Water should be added from time to time to keep the liquid up to fifty gallons. Store in air-tight hardwood barrels. Test the strength of the solution with a Baume hydrometer and dilute for use according to the following table (see also p. 1029):

Dilutions For Dormant And Summer Spraying With Lime-sulfur Mixtures

Emulsions.—Emulsions are oily or resinous sprays in which these substances are suspended in water in the form of minute globules, a condition brought about by the addition of soap. They form an important class of contact insecticides, useful particularly against scale insects and plant-lice.

Kerosene emulsion.—Kerosene emulsion is the oldest of our contact insecticides. It is especially valuable for use against plant- lice and other small, soft-bodied insects. It is prepared by the following formula: Soap, one-half pound; water, one gallon; kerosene, two gallons. Dissolve the soap in hot water; remove from the fire and, while still hot, add the kerosene. Pump the liquid back into itself for five or ten minutes or until it becomes a creamy mass. If properly made, the oil will not separate on cooling. For use on dormant trees, dilute with five to seven parts of water. For killing plant-lice on foliage, dilute with ten to fifteen parts of water.—-Crude-oil emulsion is mode in the same way by substituting crude oil in place of kerosene. The strength of oil emulsions is frequently indicated by the percentage of oil in the diluted liquid: for a 10 per cent emulsion, add seventeen gallons of water to three gallons of stock emulsion; for a 1.5 per cent emulsion, odd ten and one-half gallons of water to three gallons of stock emulsion; for a 20 per cent emulsion, add seven gallons of water to three gallons of stock emulsion; for a 25 per cent emulsion, add five gallons of water to three gallons of stock emulsion.

Distillate emulsion. — Distillate emulsion is widely used in California. Distillate (28° Baume), twenty gallons; whale-oil soap, thirty pounds; water, twelve gallons. Dissolve the whale- oil soap in the water which should be heated to the boiling point, add the distillate and agitate thoroughly while the solution is hot. For use, add twenty gallons of water to each gallon of the stock solution.

Carbolic acid emulsion.—This spray is used in California for mealy-bugs, plant-lice, and the soft brown scale: Whale-oil soap, forty pounds; crude carbolic acid, five gallons; water, forty gallons. Dissolve the soap completely in hot water, add the carbolic acid, and heat to the boiling point for twenty minutes. For use, add twenty gallons of water to each gallon of stock solution.

Miscible oils.—There arc now on the market a number of concentrated oil emulsions, known as soluble or miscible oils, intended primarily for use against the San Jose scale. For this purpose they are fairly effective when diluted with not more than fifteen parts of water. To lessen danger of injury to the trees, applications should not be made when the temperature is below freezing, nor when the trees are wet with snow or rain. Methods have been devised for preparing these concentrated emulsions at home, but as there is considerable danger attending the process, it is better to buy them ready-made.

Tobacco.—Tobacco is one of our most useful insecticides. The poisonous principle in tobacco is an alkaloid nicotine, which in the pure state is a colorless fluid, slightly heavier than water, of little smell when cold and with an exceedingly acrid burning taste even when largely diluted. It is soluble in water and entirely volatile. It is one of the most virulent poisons known; a single drop is sufficient to kill a dog. Commercial tobacco preparations have been on the market for many years. The most important of these are block leaf, "black leaf 40," and nicofume.

Black Leaf.—Black leaf was formerly the most widely used tobacco extract. It contains only 2.7 per cent nicotine and has now been replaced by the more concentrated extracts. It is used for plant-lice at the rate of one gallon to sixty-five gallons of water.

"Black leaf 40."—"Black leaf 40" is a concentrated tobacco extract containing 40 per cent nicotine sulfate. Its specific gravity is about 1.25. In this preparation the nicotine is in a non-volatile form, it having been treated with sulfuric acid to form the sulfate. "Block leaf 40" is used at strengths varying from one part in 800 parts of water to one part in 1,000 parts. It can be satisfactorily combined with other sprays, as for example, lime-sulfur solution, arsenate of lead, and the various soap solutions. When used with water, about four pounds of soap should be added to make the mixture spread and stick better.

Nicofume is a tobacco extract containing 40 per cent of nicotine in the volatile form. It is intended primarily for use in greenhouses. Strips of paper soaked in this preparation are smudged in greenhouses to destroy aphids.

Tobacco is also used in the form of dust for the same purpose. It is especially valuable against root-lice on asters and other plants. Tobacco extracts can be made at home by steeping tobacco stems in water, but as they vary greatly in nicotine content and are sometimes likely to injure tender foliage, it is better to buy the standardized extracts.

Pyrethrum.—A very fine, light brown powder, mode from the flower-heads of species of pyrethrum. It is scarcely injurious to man. Three brands are on the market:

Persian insect-powder, made from the heads of Pyrethrum roseum, a species also cultivated as an ornamental plant. The plant is native to the Caucasus region.

Dalmation insect-powder, made from Pyrethrum cinerariae folium.

Buhach, made in California from cultivated plants of Pyrethrum cinerariae folium.

When fresh and pure, all these brands appear to be equally valuable, but the home-grown product is usually considered most reliable. Pyrethrum ^soon loses its value when exposed to the air. It is used in various ways:

(1) In solution in water, one ounce to three gallons. Should be mixed up twenty-four hours before using.

(2) Dry, without dilution. In this form it is excellent for thrips and lice on roses and other bushes. Apply when the bush is wet. Useful for aphis on house plants.

(3) Dry, diluted with flour or any light and fine powder. The poison may be used in the proportion of one part to from six to thirty of the dilutent.

(4) In fumigation. It may be scattered directly upon coals, or made into small balls by welting and molding with the hands and then act upon coals. This is a desirable way of dealing with mosquitos and flies.

(5) In alcohol, (a) Put a part of pyrethrum (buhach) and four parts alcohol, by weight, in any tight vessel. Shake occasionally, and after eight days filter. Apply with an atomizer. Excellent for greenhouse pests. For some plants it needs to be diluted a little. (b) Dissolve about four ounces of powder in one gill of alcohol, and add twelve gallons of water.

(6) Decoction. Whole flower-heads are treated to boiling water, and the liquid is covered to prevent evaporation. Boiling the liquid destroys its value.

Good insect-powder can be made from Pyrethrum roseum, and probably also from P. cinerariaefolium, grown in the home garden.

Bait, vegetable bait.—Spray a patch of clover or some other plant that the insects will eat with paris green or some other arsenical; mow it close to the ground, and while fresh place it in small piles round the infested plants. To avoid wilting of the bait, cover the heaps with a shingle or piece of board.

Bran-arsenic mash.—White arsenic, one-half pound, or paris green, one pound; bran, fifty pounds. Mix thoroughly and then add enough water to make a wet mash. Sugar or molasses may be added, but is unnecessary. Poisoned baits are used against cutworms and grasshoppers.

Kansas grasshopper bait.—This bait is the most efficient means of controlling grasshoppers yet devised. It is prepared as follows: Bran, twenty pounds; paris green, one pound; syrup, two quarts; oranges or lemons, three fruits; water, three and one-half gallons. Mix the bran and paris green thoroughly in a wash-tub while dry. Squeeze the juice of the oranges or lemons into the water; chop the pulp and peel fine and add them also. Dissolve the syrup in the water and wet the bran and poison with the mixture, stirring at the same time so as to dampen the mash thoroughly.
Sow the bait broadcast in the infested area early in the morning.

Criddle mixture.—Mix one pound of paris green with one-half barrel of horse droppings, and add one pound of salt if the material is not fresh. For use against grasshoppers.

Gas tar is used extensively for painting wounds to keep out the moisture and prevent the entrance of insects. It is also sometimes used on peach trees to keep out the borers. In this case it should be applied in the spring only, as there is danger of injuring the trees in the fall.

Asphalt.—Certain grades of asphalt have been used successfully on peach in California to keep out the Pacific peach tree-borer. Experiments in the eastern states indicate that it may be used to advantage against the common peach tree-borer.

Hot-water.— Submerge affected plants or branches in water at a temperature of about 125°. For aphis. It will also kill rose-bugs at a temperature of 125° to 135°.

Gasolene torch.— The gasolene torch has been successfully used for the control of scale insects on date palms in Arizona. The trees are first pruned closely, drenched with gasolene and fired. They are then scorched with a gasolene Blast torch.

Flour paste.—Mix a cheap grade of wheat flour with cold water, making a thin batter, without lumps; or wash the flour through a wire screen with a stream of cold water. Dilute until there is one pound of flour in each gallon of mixture. Cook until a paste is formed, stirring constantly to prevent caking or burning. Add sufficient water to make up for evaporation. For use, add eight gallons of this stock solution to one hundred gallons, of water. Used for red spider in California.

General practices.

Cleanliness.—Much can be done to check the ravages of insects by destroying their breeding-pi aces and hiding- places. Weeds, rubbish, and refuse should be eliminated.

Hand-picking often still the best means of destroying insects despite all the perfection of machinery and of materials. This is, particularly true about the home grounds and in the garden. The cultivator should not scorn this method.

Promoting growth.—Any course that tends to promote vigor will be helpful in enabling plants to withstand the attacks of plant-lice and other insects.

Burning.—Larvae which live or feed in webs, like the tent- caterpillar and fall web-worm may be burned with a torch. The lamp or torch used in campaign parades finds its most efficient use here.

Banding.—To prevent the ascent of canker-worm moths and gypsy-moth caterpillars, various forms of sticky bands are in use. For this purpose there is no better substance than "tree tangle-foot." It may be applied directly to the tree-trunk, but when so used leaves an unsightly mark and requires more material than when the following method is used: First place a strip of cotton batting 3 inches wide around the trunk; cover this with a strip of tarred paper 5 inches wide; draw the paper tight and fasten at the lap only with three or four tacks. Spread the tanglefoot on the upper two-thirds of the paper, and comb it from time to time to keep the surface sticky. Burlap bands are made by tying or tacking a strip of burlap around the trunk and letting the edges hang down. The larvae will hide under the loose edge, where they may be killed. Banding U now little used for codlin-moth, since spraying with poison has been found so much more effective.

Fumigation.

Poisonous gases are widely used in killing insects under certain conditions. Hydrocyanic acid gas is employed in the fumigation of greenhouses and citrus trees. It is a most deadly and effective material. In Europe, fumigation with this gas is known as cyaniding and cyanization. Nicotine preparations are used extensively in greenhouse fumigation. Carbon bisulfid is employed almost exclusively for the treatment of stored grains and seeds.

Hydrocyanic add gas.—This gas is generated by adding potassium or sodium cyanide to dilute sulfuric acid. The gas is a deadly poison, and great care should be taken not to inhale it. One breath is fatal!

Potassium cyanide is a white amorphous salt that readily absorbs moisture when exposed to the air. Pure potassium cyanide contains 40 per cent of cyanogen (CN) by weight. When potassium cyanide (KCN) is placed in dilute sulfuric acid the cyanogen (CN) unites with the hydrogen (H) of the acid (H2SO4) to form hydrocyanic acid gas (HCN). In the preparation of this gas for fumigation purposes use a potassium cyanide which is at least 98 per cent pure. The chemicals should always be combined in the following proportions: Potassium cyanide, one ounce; sulfuric acid, one fluid ounce; water, three fluid ounces.

Always use an earthen dish, pour in the water first, and add the sulfuric acid. When all is ready, drop in the proper quantity of potassium cyanide and retire immediately, before the gas arises. Fig. 1323 shows a device used abroad (from the "Gardening World") for dumping the cyanide (at 4) into the acid by means of a cord that extends outside the house.

White-fly.—The quantity of chemicals used for a given space will depend on the nature of the insects to be killed and the susceptibility of the plants to injury. This quantity is usually indicated by amount of potassium cyanide required for each 100 cubic feet of space. For treating white-fly on tomatoes in greenhouses, use one ounce to 3,000 cubic feet, letting the fumigation continue all night. The same treatment applies for cucumber. Fumigate on dry, dark nights when there is no wind. The house should be as dry as practicable and the temperature not above 60° F.

Greenhouses.—-No one formula can be given for fumigating with hydrocyanic acid gas the different kinds of plants grown in greenhouses; as the species and varieties differ greatly in their ability to withstand the effects of the gas. For the general run of greenhouse subjects, the practice is to use one ounce of potassium cyanide, one ounce of sulfuric acid, two ounces water, to each 2,000 cubic feet of space. The cyanide should be 98 per cent pure. Fumigate at night when there is no wind and when the plants are dry and the house cool; leave the house closed till morning, and open it up and let it air out before entering it. This applies to chrysanthemums, cinerarias, azaleas, bulbs, carnations and other common plants.

Ferns and roses are very susceptible to injury, and fumigation, if attempted at all, should be performed with great care. In cases of doubt, or when there is reason to suspect that the plants are particularly susceptible, and when one does not have definite instructions, it is well to fumigate with the weakest strength in use, and increase it in subsequent fumigations if the insects are not killed and if the plants are not injured.

Violets are very susceptible to injury from tobacco fumigation, and commercial growers therefore regularly use hydrocyanic acid gas for the control of green-fly" and "black-fly," two species of plant-lice. The latter is much more difficult to kill. For over-night fumigation from one- fourth to onfr-half ounce potassium cyanide to each 1,000 cubic feet is generally used. Sometimes one ounce potassium cyanide to each 1,000 cubic feet is used, the fumigation continuing only from twenty-five to thirty-five minutes. This treatment is more likely to injure the plants. Violets may be injured severely by the gas without the leaves being burned. This injury consists in a weakening of the plants which defers blooming for several weeks.

Dormant nursery stock may be fumigated with hydrocyanic acid gas in a tight box or fumigating-house made especially for the purpose. Fumigating-houses are built of two thicknesses of matched boards with building-paper between, and are provided with a tight-fitting door and ventilators. The stock should be reasonably dry to avoid injury, and should be piled loosely in the house to permit a free circulation of the gas. Use one ounce of potassium cyanide for each 100 cubic feet of space, and let the fumigation continue forty minutes to one hour.

A fumigating-house is shown in Fig. 1324 (from a bulletin on "The San Jos6 Scale," by A. E. Stene. of the Rhode Island State Board of Agriculture and College of Agriculture). It is a house or box as nearly airtight as possible. The floor should have a movable slat grating on which the plants may be laid, some distance from the ground, to allow of circulation of the gas. The house shown in the cut is 8 feet high in front and 6 feet in rear, and the larger room contains 980 cubic feet, requiring approximately ten ounces of cyanide. The other rooms allow of smaller quantities to be fumigated. The doors opening from the outside provide quick discharge of the air when fumigation is completed.

Fumigation of citrus trees.—In this case, the tree to be fumigated with the hydrocyanic acid gas is covered with an octagonal sheet tent (Fig. 1325) made of six and one-half ounce special drill or eight-ounce special army duck, and the gas is generated in the ordinary way beneath it. The tent is so marked that when in position it is an easy matter to determine the distance over the tent and the circumference at the ground. When these figures are known, the proper dosage may be obtained from the following chart, which has been prepared for a strength of one ounce of cyanide for each 100 cubic feet of space:

The top line of numbers, beginning at 16 and continuing to 68, represents the distance in feet around the bottom of the tent. The outer vertical columns of larger numbers running from 10 to 49 represent the distance in feet over the top of the tent. The number of ounces of cyanide to use for a tree of known dimensions is found in that square where the vertical column

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==Cultivation==
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===Propagation===
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===Pests and diseases===
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==Species==


==Gallery==
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==References==
*[[Standard Cyclopedia of Horticulture]], by L. H. Bailey, MacMillan Co., 1963




==External links==
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