University of Vermont Extension 
Department of Plant and Soil Science

Summer News Article


Dr. Leonard Perry, Extension Professor
University of Vermont
Got holes in your leaves of vegetables, flowers, and perennials such as hostas?  Then you may well have slugs eating them.  A slimy trail on leaves is proof the chewing is from slugs and not other chewing insects.  There are several methods to control slugs with little or no adverse effect on the environment.

The first fact to know is that slugs are not insects, so insecticides generally wont work on them.  Slugs actually are mollusks, related to oysters, clams, and shellfish.  They are like snails, only without an outer shell.  There are over 32 species of slugs in the U.S., with some in the Pacific Northwest several inches long!  Both slugs and snails “eat” leaves by rasping them with a horny file in their mouths.

Slugs mainly feed at night, retreating by day into moist places—under leaves, boards, flowerpots, mulch, or similar.  These areas, too, are where they lay their eggs.  Slugs develop and multiply most when both hot and moist, maturing in about a year.  They tend to go dormant when hot and dry in summer, and of course over winter.

So keeping the slug habitat in mind, a good method of control is to modify these ideal conditions.  Keep moist leaves and mulch out of beds where they are prone to congregate and eat leaves.  Pick off or “deleaf” lower leaves of plants such as hostas, allowing more air circulation.  Remove plant refuse such as pea or bean vines as soon as you’ve finished the harvest.
Avoid watering in the evening so your soil surface goes into the night dry. This alone can reduce slug damage by up to 80 percent.

There are several other mechanical means to control slugs.  Some place boards or shingles in gardens that slugs can hide under, then collect them from under these by day.  Slugs will congregate in a roll of wet newspaper you can then just throw away.

Some collect slugs in saucers of beer to which they are attracted.  Or, you can substitute water containing a pinch of baker’s yeast, or an overturned melon half.  One recipe calls for a quart of warm water, a packet of dry yeast, a pinch of sugar, and some molasses or honey.  If using a can sunk in the ground to hold your liquid of choice, just make sure the rims are about a half inch above ground.  Slugs can crawl over this, but it prevents ground beetles from falling in.  Many of these beetles are beneficial in the garden, eating insects, sometimes even slugs.

Create barriers.  Wire fly screen, as from windows, can be cut into strips four inches wide and set around plants. This also can be tacked around coldframes.  Slugs can be controlled as well by placing copper strips around plants, set on edge like a fence, although with recent rises in copper prices this might get rather expensive.  The slugs don’t like to cross the copper. Some have had success wrapping a copper wire gently around stems, as of tomatoes. Just make sure the wire doesn’t constrict the stems as they grow.  Or cut the top and bottom off of plastic bottles and place these around stems.  Sink them a couple inches in the ground.  There is even an electronic slug and snail “fence”.
An inexpensive barrier slugs don’t like to cross is a thin band of wood ashes around plants, or coffee grounds.  If you are near the coast, or have access to seaweed, this too repels slugs.  It is salty, and they don’t like salt.  When seaweed dries it becomes rough, something else slugs don’t like.   Diatomaceous earth is composed of sharp, jagged skeletal remains of microscopic creatures
which pierce soft-bodied pests causing them to dehydrate.  It can be mixed with water and sprayed on plants too.  You’ll have to spread more of this around plants after a rain.  Sharp sand, or broken egg shells last after rains (although the shells can be blown about).

There are slug baits in various forms you can find in garden and hardware stores.  These often contain the chemical metaldehyde.  If using, follow all label directions and precautions.  These baits may be less effective after rains, the time when slugs are most active.  Keep in mind these pesticide baits often resemble pet food, so can poison pets, songbirds, slug predators, and even children that might come in contact with them. As an alternative, look for much safer garlic-based sprays.

If you are a night owl and want to go after slugs directly, take a salt shaker with you to the garden along with flashlight.  Sprinkling salt on them, as well as misting them with an ammonia solution (70 to 80 percent mixed in water) will show instant results.  If this sounds too evil, just remember this instant death is much quicker than that caused by most pesticides.

You may need to do little of these control methods if you promote their natural enemies.  Toads, snakes, birds, turtles, ducks, and even chickens will eat slugs.  Some of the birds known to eat slugs include blackbirds, thrushes, robins, starlings, jays, seagulls, and owls.  If your main problem is on hostas, try growing more slug-proof selections—those with puckered or thick blue leaves.  Or try a trap crop, a crop such as lettuce that slugs prefer, interplanted among your other plants.  These will attract the slugs that can then be dealt with all in one place.

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