There are a number of methods of controlling snails and slugs. First of all, remove their hiding places by cleaning up boards, stones, and other debris. Their activity can be limited further by getting rid of any weeds so that the soil dries out more rapidly. If practical, eliminate ground cover plants which harbor these pests. Hand-picking is time consuming but can be effective when done frequently. Draw the snails out by watering the yard in the afternoon. Then go back after dark and collect them. Do this daily when snails are troublesome. One way to keep these pests out of vegetable gardens or away from individual plants is to use a barrier of an irritating substance. They won’t cross over materials like wood ashes, lime, or coarse sand. Place one of these in a band (1 inch wide) around areas to be protected. Barriers are most effective where they remain dry. Often the quickest, most successful control of snails and slugs comes with the use of chemical baits. Baits contain either mesurol (methiocarb) or metaldehyde. If you’ve tried snail baits before without any luck, you may have been using a metaldehyde bait during moist, cool weather. Metaldehyde is not effective when days are cloudy, foggy, or rainy. Mesurol bait is effective under both dry and moist conditions.
Mesurol cannot be used in the vegetable garden. Bait containing metaldehyde can be placed near plants grown for food as long as it does not contact the edible part of the plant. Where a root crop like carrots or beets is involved, place bait on the soil surface away from the plant so that it is not washed onto the edible root. Or, a barrier of bait can be used along the edge of the garden to intercept snails and slugs as they crawl in. It is also helpful to bait areas where they hide.
Apply baits in the late afternoon or evening and repeat applications 2 to 3 times at about 2 week intervals. Do not apply bait in piles, but scatter it lightly over the infested areas. Just before application, water the area, then do not water again for at least 3 days.