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Spokane, Washington  Est. May 19, 1883
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Gardening: Slugs get busy in high humidity in spring, fall

A leaf shows a bunch of holes in it caused by slugs last August. (COURTESY PHOTO / Susan Mulvihill)
A leaf shows a bunch of holes in it caused by slugs last August. (COURTESY PHOTO / Susan Mulvihill)

It’s slug season. I’ve already had them eating on some of my plants including one fresh from the garden center.

Slugs are related to snails but without the shell. With no protection from the elements, their moist bodies are very susceptible to drying out and so they live in moist environments close to the soil under leaf litter, low hanging leaves or other debris. They generally feed at night when the humidity is higher and the temperatures cooler and are most active in the spring and again in the fall. In general, they are active between 38 and 88 degrees.

Slugs feed on a wide range of plants including hostas; leafy vegetables like lettuce, cabbage, beans, peppers and zucchini and flowers like dahlias, zinnias, delphiniums and marigolds. Keep in mind, this is not a complete list by any means. Plants slugs tend to avoid include lady’s mantle, lavender, ajuga, iris, columbine, hellebores, peonies and geraniums. Most of these plants have thick, tough or hairy leaves.

Slugs don’t bite leaves. Rather they have rasping mouth parts that scrape the leaf surface, leaving behind random ragged holes and thin places between veins or along the edges. In some cases, they will devour an entire leaf and if there are enough of them they can wipe out an entire row of lettuce in a matter of days.

Successfully dealing with slugs is a multistep process. First, if you notice damage, do some garden clean up around susceptible plants. Remove garden debris, leaf litter, boards, rocks or anything else that shelters the soil. Lightly cultivate around the plants on a hot afternoon to expose them to the heat and drying winds. Repeat this in the fall before the slugs hibernate and again in the spring as temperatures begin to rise.

Set out some cheap beer in shallow tuna or cat food cans. Slugs are attracted to the smell of fermenting grain which is basically what beer is. Set the can so the rim is at the soils surface and fill it half full of beer. The slugs will crawl in and drown. Check the traps regularly, empty and then refill them.

Make your garden an attractive place for predators like frogs, birds and beetles. These animals like nothing better than a tasty meal of slugs and a lot of other garden pests. Best of all they will be working for you 24/7 for the price of providing some food, shelter and water.

Iron phosphate slug baits such as Sluggo or Escar-go are very effective for controlling slugs. They come as grain-base granules that are easy to spread and are nontoxic to other animals and insects. Pellets should be scattered four to six per square foot for effective coverage.

One last, but somewhat expensive method of slug control is to lay down thin copper.

Pat Munts has gardened in the Spokane Valley for over 35 years. She is co-author of Northwest Gardener’s Handbook with Susan Mulvihill. She can be reached at pat@inlandnwgardening.com.

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