Sandra Mason: Keeping hungry slugs out of your garden

Sandra Mason: Keeping hungry slugs out of your garden

I love to graze my garden, especially when ripe, juicy strawberries are ready for plucking. However, my recent experience has tempered my love of grazing.

Just as I was ready to indulge in one of my last strawberries, I happened to notice someone (or something) else had beat me to my gastronomic delicacy. There in its slimy slippery glory was a tiny slug totally gorging its hermaphroditic self on my intended joy. UGH!

Rainy, humid weather is perfect for slug smorgasbords. Slugs can cause heavy damage on thin-leaved plants growing in shady areas such as hostas and impatiens.

With prolonged rainfall, slugs expand into sunnier areas, feeding on a wide range of plants including lettuce, spinach, petunias, chrysanthemums, daisies and begonias. Seedlings may be stripped of all their leaves virtually overnight.

The most common species is the gray garden slug, which is usually about 3/4 inch long but may be up to 11/2 inches long. Although called gray, they come in white, yellow, lavender, purple or blackish with brown specks and mottled areas.

Plant damage appears mainly as ragged holes in the middle of the leaf rather than along the margins. Slugs quickly dehydrate in the sun, so they feed mainly at night or on foggy, rainy days. They are safely tucked away in moist mulch when you are lamenting about plant damage. Since slugs produce lots of slime as they move, their tell-tale signs of silvery slime trails may be seen on the plant or on sidewalks during the day.

Our recommended gardening technique of mulching with organic mulches has a dark side since it can also increase slug populations during wet weather. Plus, our continuous plantings of hostas create slug highways.

Habitat modification is one of the most effective strategies in reducing slug populations. At least during wet weather, you may want to pull organic mulch away from plants heavily damaged by slugs. Once weather dries and heats up, pull mulch back around plants. Avoid watering late in the day since this creates moist conditions conducive to slug activity.

Older slug baits contained metaldehyde, which is quite toxic to mammals and birds. Newer baits made with iron phosphate are safer but can still cause vomiting in dogs. As with all pesticides, use according to label directions to lessen exposure to people and nontarget animals.

With high-value plants, copper strips that extend an inch or more below and above the soil line will keep out slugs. The copper apparently generates an electrical charge as a slug zapper.

Most other slug remedies are not reliably effective. The mucus that slugs produce allows them to cross the edge of a razor blade without harm; therefore, the use of sharp gravel or cinders is of questionable value. Beer in shallow dishes can be effective in drowning some slugs, but has little benefit in large areas. Diatomaceous earth is helpful if it stays dry, so it is not very effective during wet weather. Salt, lime and other chemicals may disrupt the soil fertility until nothing will grow. Because slugs are mollusks, insecticides are not effective; however, I heard a saut pan with garlic and butter is particularly effective. Bon apptit!

Garden walks

— From 9 a.m. to 4 p.m. on June 22, the Champaign County Master Gardener Garden Walk will feature eight gardens and plenty of shopping at the Idea Garden. Visit area garden centers for tickets. For more information, call 333-7672 or visit

— The Iroquois County Historical Society Garden Walk and Garden Faire will take place June 29-30 with gardens in the Donovan/Iroquois area and Faire at Iroquois Park. For more information, call 815-432-2215.

— From 3 to 7 p.m. on June 30, the Village Gardeners Garden Walk will take place in St. Joseph, featuring six stops. Visit area garden centers for tickets. Also, you can purchase tickets on walk day from 2:45 to 5 p.m. at the southeast corner of Main Street and U.S. 150.

Sandra Mason is unit educator, horticulture and environment, for the UI Extension, Champaign County. Contact her with questions or comments at 801 N. Country Fair Drive, Champaign, IL 61821, call 333-7672, email or fax 333-7683.

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