Hosta growers always seem to have more than their share of slugs. During drought years, slugs almost disappear from sight. Prolonged periods of wet weather, however, have the opposite effect and numbers become noticeable. The grey garden slug, Agriolimax reticulatum, starts very small (less than one-quarter inch) and grows to almost 1 inch in length.
Slugs require a damp environment to survive. They are protected from drying by hiding during the day and feeding at night. Slugs may be found during the daytime by looking under boards, rocks, mulch that had been placed or the foliage of low dense plants.
When slugs are abundant, considerable damage may accumulate on certain hostas. Damage is usually most severe on thin-leafed varieties or in the white margins and centers of variegated varieties.
There is no single, foolproof remedy for slugs, although several common practices can help. Start by cleaning debris from the garden to eliminate slug hiding places. Remove heavy leaf litter, boards, bricks, unnecessary mulch, and other debris in contact with the ground. Dense ground covers that are harboring slugs can be thinned to promote sunshine, air circulation, and drying.
Minor slug problems can be controlled by handpicking. Check carefully around the base of damaged plants and favored hiding places. Night checking with a flashlight or leaving “trap sites” may improve your efficiency. A mild solution of vinegar or ammonia can be sprayed on individual slugs. This, like the apparently factual urban legend of sprinkling salt on slugs, will kill individual slugs but is too labor-intensive for complete success.
Beer is a well-known trap attractant for slugs, though any fermenting or yeast-containing liquid appears to work. The traditional trap design is to bury a shallow pan in the soil with the top edge level with the soil surface. Renew the beer or attractant regularly and empty the pan of trapped slugs frequently.
Chemical treatment occasionally may be necessary. Chemical control of slugs requires a special type of pesticide called a molluscicide. Slug baits can be effective when used in conjunction with the other methods discussed above. The most commonly available baits contain metaldehyde and/or carbaryl combination in liquid, granular, or pelleted baits. These baits can be hazardous if carelessly used where children and pets can be exposed. A newer snail and slug bait contain iron phosphate, an ingredient that is nontoxic to children, pets, and wildlife.
Do not pile slug bait in mounds or clumps. Thinly scatter bait in small spots or narrow strips around susceptible plants and moist, protected locations. Treat at the first sign of damage. Baiting is less effective during very hot, very dry or cold times of the year.