Slug Stoppers

Slugs can do a lot of damage to tender plants. Learn how to stop them.

April 25, 2011

Every gardener with a moist, shady area knows slugs are pigs. With their rough, file-like tongues, these mollusks devour several times their own body weight in one night, leaving gaping holes in leaves, torn foliage, and-yuck!-slime trails in their wake. Hostas and lettuce are their most common targets, but corn, beans, strawberries, annual flowers, and many other garden favorites are susceptible to attacks. In our test gardens, we've battled the slimers and tried a many different strategies for controlling them. The following tactics work best for us.

Beer trap. This type of trap works because slugs are attracted to the fermented yeast in beer. In a study by Whitney Cranshaw, Ph.D., professor of entomology at Colorado State University, nonalcoholic Kingsbury Malt Beverage was found to attract the most slugs. Michelob and Budweiser placed second and third out of the 12 beverages tested. (We're still waiting for the results from the gardeners' taste test.) "Take a shallow container (such as a sour cream or yogurt cup) and bury it so that it is even with the soil level," explains gardening expert Willi Evans Galloway, who gardens in Seattle. "Then fill the container with beer to within an inch of the rim. The slugs crawl in and drown." For best results, change the beer every few days.

Diatomaceous earth (DE).
After testing all kinds of slug barriers, Jeff Gillman, author of The Truth about Garden Remedies and professor of horticulture at the University of Minnesota, concluded that DE is the most reliable. "DE is a white powder made from the fossilized remains of diatoms, one-celled algae that have a skeleton made of silicon," Gillman says. "To a slithering slug, this lethal powder is extremely sharp and cuts their undersides, causing dehydration." DE does have to be replenished each time it rains, making it a better choice for climates where it does not rain frequently. (Note: Buy only untreated diatomaceous earth formulated for garden use, and wear a dust mask when applying it. DE made for swimming pools is chemically altered and not suitable for use in any garden, much less an organic one.)
You can buy bags of Diatomaceous earth at Gardener's Supply or Planet Natural.

Copper barrier. When a slug crosses a copper barrier, its moist, mucusy body reacts with the copper and it receives an electric shock. Copper barriers can be pushed into the soil to make a vertical fence around a plant or bed, or laid flat. Either way, use 2- to 3-inch strips. Yes, this product can be costly, so save it for your most prized plants or where the slugs are congregating. Rolls of copper barrier are sold at Planet Natural.

Sluggo. This nontoxic slug bait (iron phosphate is the active ingredient) is safer than metaldehyde baits, which can harm pets and wildlife. Sprinkle Sluggo granules around your plants and beds in the evening. Ingesting Sluggo causes slugs to stop feeding and to retreat underground, where they die within three to six days. Galloway tested Sluggo and found that it works well as long as you consistently reapply (about once a week). She uses it in conjunction with beer traps for better control. In dryer regions, you may need to reapply only every two weeks. Sluggo is sold at Gardener's Supply or Harvest Safe.

Red clover. Slugs love this easy-to-grow legume, concludes a recent study from Harper Adams University College in Shropshire, England. Researchers found that when this alternative source of food was planted next to beds, slugs were lured toward the sacrificial clover and away from more valuable plants. Resilient (and beautiful), red clover grows in a wide variety of soils. While the clover lasts, this method substantially reduces slug damage. After it fades, cut it down and incorporate it into the soil as nitrogen-rich organic matter.

Hand-picking. Not every gardener enjoys this (though we know some of you find it to be wicked fun), but the results are guaranteed. "I have yet to find a slug control that is more surefire and easy than a daily hand-picking patrol when pressure is high," Debbie Leung claims. In the early morning and early evening during slug season, pluck as many slugs as you can find (Debbie sometimes collects 200 in a day). Cut them in half or drop them in soapy water to kill them. For easier picking, encourage slugs to congregate by laying wooden boards or roofing shingles along garden paths for slugs to hide under. So which method works best? None of them control slugs 100 percent of the time, but our experience finds that any of the methods combined with hand-picking keeps slugs and their damage to a minimum.

 

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