Concentrate your slug and snail control efforts early in the garden season as the weather begins to warm and these pests begin to feed and reproduce. Follow-up regularly to eliminate those undetected or newly hatched.
Slugs and snails are grayish or brownish worm-like mollusks 1 to 2 inches long with legless bodies. Snails have spiral shells; slugs do not. Females lay white eggs encased in slime buried in the soil. Young slugs and snails look their parents only smaller.
Methods to control slugs and snails in the garden:
• Hand-picking. Handpick snails and slugs by flashlight at night when they are most active. Drop them into a can or bucket of soapy water where they will drown or kill them by sprinkling table salt on them or crush them. In the vegetable garden, search for slugs and snails near and on leafy crops and also on and around maturing fruiting crops such as strawberries and tomatoes.
Like other mollusks, snails and slugs need to be moist at all times. During the day, they retreat to cool, damp, dark hiding places—under low growing plants or under boards or flower pots. At night they move about freely to feed–even crossing sidewalks and driveways. They are most active beginning about two hours after sunset until about two hours before sunrise. This is when searching out and handpicking slugs and snails is the most effective.
Look for slugs and snails around the stems of plants and also under leaves well up into the plant. The slimy mucus slugs and snails secrete to move over dry surfaces also acts as an adhesive which allows them to move upside down on plant stems and leaves. The mucus also can act as a thread which will allow slugs to lower themselves from one leaf or branch to another as they feed.
In cold weather, search for slugs near the crown of perennial plants where they burrow under to feed on roots. Snails set a hard, transparent film across their shell opening during cold weather and will shelter under boards and plants.
• Trapping. To trap and handpick snails and slugs during the day, place a wide board, a shingle, or an upturned flower pot alongside plants that need protection. The pests congregate in dark, damp places where the soil is moist and or where there is damp mulch or acidic organic material. (They cannot tolerate dry weather or dry or alkaline soil.) Each morning turn over the cover and collect and crush the pests or kill them with a spray solution of 1:1 household ammonia and water.
• Drowning. Drown slugs and snails by placing a shallow pan or tin can with the lip just below soil level filled with beer or 1 teaspoon of baking yeast in 3 ounces of water near plants where the pests feed. Slugs and snails are attracted to the yeast; when they come to drink, they fall in and drown.
• Barriers. Snail and slug bodies are soft and sensitive to sharp objects. Sprinkle diatomaceous earth (ground up, powdery prehistoric shellfish), wood ashes, or fine sand around plants you want to protect. The sharp, gritty edges will deter these soft-bodied pests; they are unable to exude enough slime to get over gritty or sharp edges. Once these barriers become wet with rain or irrigation, snails and slugs cab slide across them on a film of water. Dry chaff and straw and wilted vegetation spread around vegetables seedlings or plants also will act as a barrier.
• Copper barriers. Strips of copper at least 2 inches wide can be used as a barrier along the edges of raised beds. Copper reacts electrochemically to the slug and snail slime and deters the pests from crossing over. Install copper strips in dry weather. Be sure to eliminate snails and slugs trapped inside the barrier because they can’t get out either.
• Soil additives. Mix coarse river sand into humus-rich garden soil; soil that is rich in acidic organic materials attracts snails and slugs but the pests will be deterred or fatally injured by the sharp edges of sand. You can also add worm castings (excrement) to your garden soil. Castings are plant nutrient rich and also alkaline; slugs and snails are deterred by the alkaline.
• Natural enemies. Slugs are a favorite food of snakes and toads (which can eat three times their weight in slugs in a day) and also fireflies.