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Slugs

By Judy Sedbrook,Colorado Master GardenerSM, Colorado State University Cooperative Extension, Denver County

Garden slugs are 1-1/2 to 2 inches long when full-grown and are gray to black in color. They are not insects but mollusks, like oysters and clams, and are often described as snails without shells. Slugs move along by secreting a path of mucus.

Hatching from masses found in damp areas of the garden, slugs are one of the first pests of spring. They begin hatching when temperatures are consistently greater than 40 degrees F. Young slugs resemble the adults and begin feeding as soon as they have hatched, creating large holes in the leaves, fruit and crowns of plants.

They prefer damp, cool locations and will hide in soil crevices, earthworm holes or under leaves, boards or other garden debris during the day. Wet weather in spring and early summer results in an increase in the slug population. If the weather is dry, they will die or burrow deep into the soil until conditions improve.

Slugs feed at night, leaving a silvery trail behind them as they move; a sure sign of their presence. They can consume several times their own body weight each night, causing serious damage in a short time.

CONTROL:

  • Stake or cage plants to keep them up off of the ground and increase spacing between them to allow air to circulate and the ground and foliage to more readily dry out.
  • Hand pick and destroy slugs as you find them; they are most active at night or in the early morning.
  • Use boards or old flower pots as traps. Slugs will tend to accumulate under them during the hot dry part of the day.
  • Stale beer placed about 1 inch deep in small, shallow containers will attract slugs. They will then fall into the container and be drowned. Empty and refill the containers as needed.
  • Baits containing the molluscicide metaldehyde give good control and may be used safely in home vegetable and flower gardens. The baits are applied directly to the soil surface, not the plants, and are most effective during dry weather.
  • A dilute concentration of household ammonia ( 5-10%) is effective when sprayed directly on the slugs.
  • Copper barrier strips, made from flashing or cut from copper sheets available from the hardware store, create a barrier to slugs. Place the copper strips around each individual plant. The copper reacts with chemicals in the bodies of the slugs and they will not crawl over it.
  • Birds may eat slugs, but are rarely active at the same time as the slugs.
  • Eliminate places where slugs may hide by removing debris, leaves and mulch.
  • Cedar chips and pine needles, used as muclch, seem to repel slugs. Pine needles should be applied 2-3 inches thick. The needles will not disturb the soil pH.
  • The use of salt to kill slugs is not recommended. It will cause problems with the soil and the surrounding plants.

For more information on slugs, see CSU Fact Sheet 5.515.

Photograph courtesy of Judy Sedbrook.

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Date last revised: 01/05/2010