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Slugs in the garden

June 17, 2009

This rainy, spring weather and the cool temperatures we've been experiencing have slowed garden growth across the entire region; perfect conditions for thriving slug populations.

While hot, dry weather can be deadly to slugs, a wet spring prompts slugs to become active early on, hatching, moving, feeding and laying eggs. Populations build when nighttime temperatures remain above 40 degrees. If you haven't seen them in your garden already, you will.

Outside of the garden, slugs can be considered beneficial because they contribute to the disposal and recycling of plant debris, helping to build soils, and because they are important prey for frogs, toads, snakes and birds. But in gardens, where slugs often find excellent conditions for growth and reproduction, they can very quickly become significant pests. They can cause considerable damage to young, succulent and newly emerging garden vegetable plants.

Slugs are gastropods (class Gastropoda), soft-bodied land mollusks (phylum Molloska). They are relatives to clams and oysters, octopi and squid. They are not insects. They do not have legs or bones of any kind and are often described as snails without shells. Without the protection of shells, these invertebrates must take shelter in shady, moist environments. Hence, they are often found beneath soil debris and under decaying wood. For every slug that you find above ground, it is quite possible that there are 10 to 20 more, in the soil.

Because of their intolerance to hot, dry conditions, slugs are mostly nocturnal, but they can be found feeding on cloudy or foggy days, or after it rains. They move about by contracting a lengthwise series of muscles, which run from head to tail along the underside of their bodies, called a foot. They can only move forward. A gland within the foot secretes mucus, which helps slugs to move more easily, while at the same time preventing them from sliding on vertical surfaces.

As slugs move, a slime trail is left behind. For gardeners, slime trails are a sure sign of their presence. Although they are often clearly visible in the morning, slime trails dry out as the day progresses, making them less noticeable.

Slugs attack a wide range of garden plants. They eat by using a radula, a coiled, tongue-like organ covered with thousands of tiny tooth-like protrusions called denticles, which rasp at the surface of plant tissue. The damage they do can be slight, or they can totally devastate a garden. They will consume almost anything leafy and green, and they will often hollow seeds out or cut seedlings off at the ground.

Although there is no simple method for eradicating slugs, several cultural practices, when used together, may provide the best overall solution.

A good first step is to eliminate debris, weeds, dense ground covers and leafy branches that are close to or lying on the ground. This allows air to circulate, keeping foliage and the ground around the plants dry.

Regular cultivation of garden soil will bring slug eggs to the surface. This will result in many of them drying out and dying. The rest will not hatch, if conditions are not right.

Hand picking is effective, but tedious. Collect and remove slugs at night, two hours after sunset, or on damp days when the slugs are actively feeding.

A damp piece of wood or cardboard, or an overturned grapefruit skin will serve as a slug trap when placed in the garden. As the day turns hot and dry, slugs will gather beneath these cool shelters, making it easy to gather them up. You can put the captured slugs in a pail of soapy water, or simply flush them down the toilet. And be sure to squash any eggs that you find.

By some estimates, slugs represent one quarter of the total diet of many frogs and toads. Because of this, many gardeners like to attract frogs and toads to their vegetable and flower gardens. This is easily done by adding a pond and/or a bog garden. Keep in mind, though, that amphibians are particularly vulnerable to the toxic effects of many pesticides.

One of the best ways to deal with slugs is to use physical barriers. Slugs will not crawl across crushed eggshells placed around and beneath individual plants. The crushed shells scratch and cut their bodies. Because of a chemical reaction that occurs between copper and their bodies, slugs will not cross copper barriers either. Copper strips can be placed around individual plants or attached to wood frames. Wooden surfaces can also be treated with copper sulfate, which is toxic to slugs.

Evidently, slugs love beer. Shallow containers, such as tuna fish cans or pie plates, can be filled with beer and placed in the ground, in the garden. Place the traps in areas where slugs are seen, making sure that the tops of the containers are at ground level. You may be surprised at how many of the slimy little critters dive right in and happily drown themselves. Clean out the dead slugs as they accumulate, and refill the containers after it rains, or as the beer evaporates.

The use of salt is not suggested. While salt will kill slugs, it may also create problems in the soil. Contact with salt can seriously damage or kill plants.



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