Snails and Slugs

Common snail (Helix aspersa)

In many parts of the world, snails and slugs are the most damaging of garden pests. Snails and slugs are almost the same, with slug just being snails without a shell. Both cause damage simply by eating the leaves and plant tissue with mouths that are under their bodies. They hide during the day, and eat at night - though they may come out on damp, gray days as well.

It's almost impossible to eradicate snails and slugs since they can come in from neighboring land, on new plants, or even as eggs in the soil of new plants. The eggs looks like clusters of pearls, about 1/8 inch in size. They're often found under boards, rocks and pots and should be destroyed.

Physical controls

Copper pipe sections as slug barriers.

They are out at night after dark, and in the early mornings - especially when it's wet, like after a light rain, or after sprinklers go off.

Hand gathering the snails and slugs (you may want to use gloves or a bag for the slugs, especially) helps control the population.
You can also just walk around the garden killing them with a hand held sprayer with 5% ammonia.
Just putting a board in the garden, elevated an inch above ground will give them a preferred hiding place. So during the day you can just lift the board and collect the snails. Squashing a snail or slug occasionally on the underside of the board helps to attract others.
Beer traps are another way to capture them. Put the beer in a saucer or other shallow container, then place that in the garden so that the lip is even with the soil level. Snails and slugs will crawl in and drown, so you should refill the liquid every day.
Copper bands and strips are a way to snail-proof areas, as they cannot cross these. A band around a citrus tree trunk or a strip around a pot or raised bed will serve to keep snails completely out.

Biological controls

Decollate snails feed on garden snails

Ducks love to eat snails and slugs.

Decollate snails feed on the brown garden snail. They will also feed on succulent leaves or berries near ground-level. They are sold in some areas, and are illegal in some areas.

Chemical controls

The most popular snail pesticides are baits which have metaldehyde or methiocarb in the form of pellets, emulsion or meal. Metaldehyde is the more widely used chemical, which is more effective in dryer, low-humidity climates. Methiocarb, which is more commonly used specifically for slugs, should be used away from fruits and vegetables. If using these in pellet form, always scatter them more loosely rather than into less effective piles. These are poisonous to dogs, who will often eat them.