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Description: Slugs are legless, boneless creatures. They are similar to snails, but have a raised mantle on the back instead of the familiar shell. Slugs are nocturnal feeders, hiding during daylight hours. There are many species of slugs capable of harming tender landscape plants or causing economic damage to greenhouse crops and field crops such as crucifers, strawberries, raspberries, potatoes, tomatoes, beans and lettuce. Most species survive the winter as eggs or adults. An adult may be a single sex or have both male and female reproductive organs (hermaphroditic) and be self-fertile. A single individual is capable of producing up to 500 eggs, which are deposited in batches of one to several dozen under stones, debris or in the soil. Eggs usually hatch in the spring or early summer. The gray garden slug is the most common and most destructive slug in this area. This 20 mm (3/4 inch) long pest varies in color from whitish yellow to nearly black, with brown specks and mottling. The tawny garden slug can reach 10 cm (4 inches) in length. It is usually recognized by its yellow mantle and lighter spots on a yellow body. This type is less common than the gray garden or spotted garden slugs. During wet growing seasons, large numbers of slugs survive the summer months and may move into gardens or cultivated fields from weedy borders, drainage ditches or other moist, sheltered areas. Landscape or crop damage is usually most severe in late summer or early autumn of cool, wet growing seasons, especially when preceded by a mild winter.
Damage: Slugs feed by grating away the surface of the plant tissue with a tooth-covered radula, which works like a rasp. This type of feeding injury is easily distinguished from caterpillar feeding on thick-leafed cole crops like cabbage. The grating action produces a large wound on the leaf surface nearest the slug, which gradually tapers to a smaller hole through the opposite surface. Slug injury to cabbage appears ragged compared with the clean-sided incision typical of caterpillar feeding. On thin-leafed crucifers or other crops, insects produce leaf injury which is virtually indistinguishable from slug feeding. The presence of a glistening slime trail can sometimes be used to distinguish slug injury. Slugs attack the fruit of tomatoes and strawberries leaving small, shallow holes in the fruit's surface. Scout for signs of slug feeding on ornamental or crop plants near the weedy borders of yards and fields. Monitoring: A covered pit can be used to provide a humid, sheltered hiding place for slugs during daylight hours. The pit should be four inches in diameter and six inches deep. An aluminum foil-covered shingle or a board can be used as a cover to provide a cool refuge from the sun. Slugs tend to congregate in large numbers in these shelters and may be counted and destroyed during daylight hours. Set monitoring traps near field and garden borders. The traps will not function as well in weedy areas or with crops such as cabbage which provide adequate shelter for slugs beneath large leaves close to the ground. Control measures should be applied when one to five slugs per trap are found. Cultural Control: - Maintain good weed control within the garden or field and along borders to eliminate daytime refuges of slugs. - Slugs avoid crawling over anything dry, dusty or scratchy, such as lime, road dust, diatomaceous earth, cinders, coarse sawdust, gravel or sand. Secretion of enough mucus to free themselves from these materials soon exhausts them and they die. A border of any of these inert materials, therefore, helps control slugs. It is also reported that hydrated lime, Bordeaux mixture or urea repels slugs. Remember, however, lime affects the pH of soil. Never use salt, as it ruins soil for most plant growth. - A fly screen, 4 inches wide, placed on edge and partly embedded in soil for support, will keep slugs out of an area. Boards, bark, or other materials not less than six inches square make effective traps when placed in gardens. Each morning you can gather the slugs from under the traps and destroy them. Slugs can also be hand-picked off garden plants at night using a flashlight and a pair of disposable gloves. However, since only a portion of the population is active on a given night, it can take quite of bit of slug harvesting before there is a noticeable impact on the population. Slugs can be kept from potted plants by supporting pots over a pan of water. - Slugs are attracted to and drown in a shallow dishes containing beer or baker's yeast dissolved in water. Set the top edges of the dish at ground level and cover loosely with a board so slugs can easily get into the mixture. - Choice of mulch can have a large impact on slug problems in flower gardens. Large bark chips and wood chips provide excellent hiding places and favor slug outbreaks. Shredded pine bark is less attractive, and cocoa hulls seem to repel slugs. - Toads are the most important natural enemy of slugs. Many people also claim that several ducks keeps a garden slug free. Chemical Control: Chemical control is generally not recommended for homeowners. Although baits containing Metaldehyde can be quite effective in slug control, they are toxic to dogs and may represent a hazard to children. Use of this material is also prohibited after edible portions of vegetables begin to grow.
Adapted
from the University of Connecticut Integrated Pest Management Program
and the
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