Although slugs are not insects, they can cause considerable damage that is not unlike insect damage. Slugs, which are mollusks, and snails look alike in the early stages, but slugs do not form a shell in their older stages. Slugs are 1/4 inch to 8 inches long, depending on the species. They vary in color from cream to grayish black, and some species are spotted. As slugs move about they leave a trail of slime.
Slugs are favored by mulch in the field and are able to overwinter in protected places beneath the mulch. They lay eggs in groups in cracks and holes in the soil. Thus, their entire life cycle can be completed in the strawberry field. Slugs require 3 to 7 months to attain adulthood. Most injury from slugs is encountered during damp, rainy spring months.
Slugs of all sizes make small, moderately deep holes in ripening berries. Most of the feeding takes place at night or on dark, overcast days; however, the Arion slug is very aggressive and has been seen feeding on bright sunny days. Holes made by the slugs can be almost anywhere on the fruit; however, feeding usually takes place under the cap. It is fairly easy to identify slug injury by the telltale slimy trail left on the surface of the fruit.
Slug control begins with the removal of nesting and breeding places such as boards, stones, trash piles, and compost piles. Traps made of wet boards or burlap bags can be set in the evening. Remove and destroy the trapped slugs in the morning. If slug damage is severe, a pesticide application might be necessary. Bait formulations usually provide control where slugs are a problem. Diatomaceous earth, a desiccant, also can be applied if a nontoxic material is desired.