Q. Many of my transplants are being eaten by something. I never see any insects, but my lettuce and spinach transplants are being devoured. Even my hostas have ragged holes chewed in the leaves. What is causing this to happen?
A. It sounds as if slugs are causing your problem. These pests prosper in the kind of wet weather we have had lately. They also thrive in soils amended with organic matter or covered with an organic mulch. You do not see them because they feed at night and hide from the heat of the sun during the day.
Slugs look like snails without the shell. They leave a shiny trail of mucous wherever they go. If you look carefully, you should be able to see this trail.
Slugs are not really insects but are classified as mollusks. Consequently, most insecticides do not control them. Pesticides containing the active ingredient metaldehyde have been available for many years and provide good control of slugs. However, this product is toxic for children and pets.
Newer products on the market use iron phosphate as the active ingredient, which is much less toxic for people, pets and other creatures. Iron phosphate is sold under trade names such as Escar-go and Sluggo. These slug baits must be re-applied after rain.
An alternative that has been used with some success is to sink aluminum pie plates into the soil around the affected plants so that the rim is at ground level. Then fill them with beer. Fortunately slugs are cheap drunks, so the least expensive beer will work fine! They are attracted to the beer, fall in and drown. Clean the traps and replenish the beer as needed. There is some evidence that beer (actually the yeast) attracts more slugs to your garden than you might have otherwise.
Other alternatives include surrounding the affected plants with coarse sand, ground eggshells or diatomaecous earth. Slugs do not like to crawl over these jagged materials. They are soft-bodied, and the sharp materials can cut them to death. They must be replenished after rain or heavy dew to be most effective.
Make sure to purchase diatomaceous earth intended for pest control rather than what is sold for use in swimming pool filters. Diatomaceous earth for pools is more finely ground and less effective.
Slugs are much less of a problem during hot, dry weather.
Send questions to Sandy Feather by e-mail at firstname.lastname@example.org or by regular mail c/o Penn State Cooperative Extension, 400 N. Lexington Ave., Pittsburgh 15208.