Slugs are an occasional problem for most Iowa gardeners. Hosta growers, on the other hand, seem to always have more than their share of slugs. During drought years slugs almost disappear from sight. Prolonged periods of wet weather, however, have the opposite affect and numbers become noticeable.
Slugs are close relatives of snails, clams and oysters. Slugs have soft, unsegmented bodies and look very similar to snails but without the external shell. When stretched out the average Iowa garden slug will be up to 1 inch in length.
Slugs require a damp environment to survive. Periodic drying that occurs in Iowa gardens may be one of the factors that limits this animal to relative obscurity except in wet years. Slugs are protected from drying by hiding during the day and feeding at night. They spend the daytime hiding in soil crevices or under boards, rocks, mulch, debris or the foliage of low, dense plants.
Feeding damage appears as large, irregular holes. When abundant, they may cause considerable damage to newly transplanted bedding plants and large-leafed ornamentals such as hostas.
Slug treatment may be occasionally necessary, but not always. Cleaning up the garden and eliminating slug hiding places may help. Heavy leaf litter, boards, bricks and other piles of damp debris in contact with the ground should be removed. 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 may improve your efficiency, or you can leave "trap sites" to be checked on a regular basis. Good slug "traps" or convenient hiding places under which the slugs will retreat include overturned pots and a piece of board or asphalt shingle.
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 control of slugs will require a special molluscicide. The most commonly available product contains metaldehyde in liquid, granular or pelleted baits. New to the market is a formulation of iron phosphate in pelleted bait form. Early research reports on iron phosphate slug bait (sold as "Sluggo") show mixed results. Let us know if it works for you. Slug batis are available for both vegetable gardens and ornamental beds. Read and follow all label directions.
This article originally appeared in the June 15, 2001 issue, p. 74.