Slugs in the Garden

Phil Peters
Adams County Master Gardener

Slugs are among the most easily recognized pests of Pennsylvania gardens. Who hasnít seen the glistening transparent slime trails left in the wake of their passage through the hosta bed? Or encountered them on a wet sidewalk? Or come across them in the woodpile or under some stone or debris in the garden?

Slugs are mollusks, gastropods to be exact. They lack the hard spiral shells of their snail cousins. They move on their bellies, actually a large foot muscle, secreting a slimy mucus trail as they do. The mucus trail facilitates their passage over uneven terrain and protects their soft underbelly from abrasion over sharp surfaces. It also helps them adhere to otherwise slippery surfaces. As the trail dries, it hardens to a clear cellophane-like ribbon betraying the passage of the pest. Slugs also secrete mucus over their entire bodies for protection and to prevent drying out.

The slug species found in Pennsylvania are drab in color, brown and gray or a combination of the two being the usual colors. Gray garden slugs are often small, ĺ to 1 inch in length. However, some species, such as the dusky slug or the leopard slug, can grow much larger, up to 2 to 4 inches when extended. This latter, Limax maximus, is the large grayish-yellow slug with black markings we see so often.

Emerging or hatching in the spring when the temperatures begin to reach above 40ļ F., slugs prefer cool, moist surroundings. Consequently they come out to feed at night and spend the day resting beneath logs, stones, leaves and plant debris or anywhere else that helps them retain their body moisture and does not get warm enough for them to begin to dry out.

The eggs are small BB-sized clear balls laid in a hollow in the earth or under logs. You may have come across these while preparing the garden since they are often laid in the same environment that the adults favor. The young that emerge in the spring become sexually mature by late summer. Each individual possesses both male and female organs, so once they have mated both can lay eggs. Mature individuals lay between 10 and 40 eggs. The adults can live up to three years, wintering over in fallen plant debris.

Even if you donít see the actual creature, the slime trail and the shredded leaf that it leads to are sufficient to tip you off to the presence of slugs in the garden. They feed on many kinds of plants grown in the garden, be it a flower garden or a vegetable garden. They especially like strawberries and hostas. This should come as no surprise as these plants offer the cover and moist environment the mollusks prefer.

While it is nearly impossible to eliminate slugs entirely, it is possible to control them and the damage they inflict. The easiest control measure is to make sure there is nowhere for them to take shelter during the day. Clean up any garden debris, organic material, leaves, wood, etc. that will afford shelter. Remove flat stones or bricks and boards from the garden area if possible. Make sure compost piles and sites for waste materials are at a distance from the garden. When mulching, apply no more than 3 inches of mulch. This will retain enough moisture for the plants but dry sufficiently to dissuade slugs from hiding in it.

There are chemical products on the market that will control slugs and snails. Be sure to read the labels carefully and follow the instructions for use as these products can be harmful to children, pets and beneficial insects. Unless you have a serious infestation, organic measures are much cheaper and can be just as effective.

If there are only occasional individuals, these can simply be picked off the plant and disposed of in a can of soapy water. Or you can trap them and dispose of the ones you catch. Setting out a board or a damp piece of burlap or newspaper in the evening will attract them beneath it. In the morning remove the slugs and drop them in a can of soapy water.

For some reason slugs are especially drawn to beer and other yeast containing liquids. One effective way to trap slugs in the garden is to bury a half-full can of beer up to its rim or set out a throw-away aluminum pan filled with some beer near where slugs are damaging plants. The slugs will be attracted to beer and die happy.

Another solution is to surround the planting with diatomaceous earth. This product may be picked up at most garden stores. It consists of the sharp shells of small sea animals. This dries and rips the foot of the slug and, consequently, they avoid crossing it. It loses its effectiveness when wet, so it must be renewed. And while copper barriers are reputed to be effective, they are more expensive and must extend into the soil as well as about 6 inches above it.

Slugs are food for many creatures normally found in our gardens: ants, some beetles and their grubs, earwigs, garter snakes, toads and turtles. So donít be hesitant to encourage these friendly species to take up residence in your yard.

If all else fails, you can always choose plants slugs do not like. Instead of soft-leaved, juicy plants like lettuce, hosta, marigolds, strawberry and many vegetables, substitute fuchsias, geranium, impatiens, lavender, and nasturtium as these are resistant to slug damage. Slugs also avoid fragrant herbs with stiff leaves such as rosemary and thyme as well as grasses and many woody ornamental plants.

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