ISU Extension News

Extension Communications
3614 Administrative Services Building
Ames, Iowa 50011-3614
(515) 294-9915

7/3/00

Contacts:
Donald Lewis, Extension Entomology, (515) 294-1101, drlewis@iastate.edu
Elaine Edwards, Extension Communication Systems, (515) 294-5168, eedwards@iastate.edu

Yard and Garden Column for the Week Beginning July 7

Garden Slug-fest

By Donald R. Lewis
Extension Entomologist
Iowa State University Extension

Ugh! Slugs! Even their name sounds ugly. Slugs are easy to hate. They work under the cover of night in your vegetable garden or your hosta patch to wreak their special kind of havoc. Ugh!

Slugs aren't always a big problem in Iowa. During drought years they almost disappear from sight. Prolonged periods of wet weather, however, have the opposite affect and numbers become noticeable.

What are they?

Slugs are snails without the spiral shell. In other words, they look like a slimy, tannish gray, unsegmented blob with little to distinguish the front from the rear (the eyes on retractable tiny stalks are at the head end). When stretched out, the average Iowa garden slug will be up to 1 inch in length.

Slugs are animals on a very large branch of the Animal Kingdom family tree called Mollusca. The best known molluscs are the clams and oysters, squids and octopuses, and snails and slugs. In spite of the impressive diversity in size and outward appearance, all these animals have a similar body plan: an unsegmented body (called the visceral mass) covered by a heavy fold of tissue (called the mantle), which may or may not include a shell, and a single muscular foot.

The slug and its closest relatives (snails, clams and oysters) are called gastropods. A majority of gastropods live in the ocean and include many of the decorative seashells found along the beach. The name gastropod literally translates from Greek to mean stomach-on-foot. The large fleshy foot that protrudes from the shell of a snail or oyster and on which they crawl, also contains the mouth opening. Gastropods rasp their food. A unique tongue-like organ with rows of minute, hard teeth is used to grate or scrape food from the crawled-upon surface and into the mouth.

Slugs feed at night except if the day is rainy, cloudy or foggy. Otherwise they remain out of sight during the daytime by hiding under mulch, leaf litter or damp debris on the ground. Slugs feed on a variety of plant matter, living or dead and decaying. They eat the tender leaves of most any seedling or transplant, the succulent foliage of plants such as hosta and herbs, flowers and soft fruits (strawberries and tomatoes). Damage generally appears as large, irregular holes of missing plant tissue.

Slugs are in that strange group of animals because each individual has both male and female reproductive organs (hermaphrodite). During mating, two individuals join to accomplish mutual fertilization.

Each mated slug proceeds to lay eggs in moist areas, up to 100 eggs apiece. Baby slugs hatch in one to three weeks and immediately begin to crawl and feed. Development to the full-grown adult stage takes from two months to a year or more, depending upon the species. Iowa slugs generally spend the winter as adults and lay eggs in early spring. New adults are present by midsummer when a second generation is started.

Management options

Slug treatment may be occasionally necessary. Clean up the garden and eliminate slug hiding places as practical. Heavy leaf litter, boards, bricks and other piles of damp debris 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. Pick off the slugs and discard. Diluted vinegar OR ammonia sprays can be spritzed onto exposed slugs with minimal chance of plant damage. The sprays appear to "dissolve" the slugs, which may have a certain appeal to you. Check for slugs at night with a flashlight to improve your efficiency. However, before you spend a lot of time with a flashlight in your garden at night, notify your neighbors so they don't report you to the police. Better yet, invite them along to join the slug hunt.

Traps may make the slugs easier to find. Place flat pieces of board, plant leaf or other material on the ground to create convenient hiding places under which the slugs retreat. Check the traps regularly, pick up and discard.

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, fill almost to the rim with beer and stand back while the slugs slither in and drown. Renew the beer regularly and empty the pan of trapped slugs frequently.

Chemical control of slugs requires a special molluscicide. The most commonly available product contains metaldehyde. Formulations available are liquid, granular or pelleted baits with labels for both vegetable gardens and ornamental beds. Read and follow all label directions before you engage in any chemical slug warfare.

-30-

ml: isugarden


Extension programs are available to all without regard to race, color, national origin, religion, sex, age, or disability.

News Menu | ISU Extension