Insect Note #9 (Revised)

Dated 5/94
Placed on the Web 4/95 by the Department of Entomology, NCSU

Slugs

Size

The size varies from less than one-half inch to more than four inches in length and from one-eight to one-half inches in width.

Color

The color varies from ash-gray or yellowish-gray to black. Some are the same basic color throughout the body; others are mottled. Immature slugs resemble adults but are smaller and usually lighter in color.

Eggs

Eggs are gelatinous and watery in appearance. They range in size from 1/8 inch in diameter to almost 1/4 inch and vary in shape from round to oval. In the colder parts of NC, only the eggs overwinter. Eggs are resistant to summer heat, excessive moisture and prolonged drying. They are laid in clusters of about 25 on the soil surface in concealed moist locations.

Life Cycle

In spring eggs hatch and young slugs appear. They resemble adults but may be lighter in color and smaller. Most slugs become mature and lay eggs in the fall of the first year of their life. If not killed by cold weather, they may live for two or more years. Slugs are active at night. Their silver-colored slime trails are quite noticeable each morning.

Feeding and Injury

Slugs feed on molds, decaying organic matter and live plant tissue. It is the damage to foliage, flowers and fruit that is significant to the homeowner. The mouth parts of slugs resemble a file with many rows of small sharp teeth, and injury to plant tissue is done by this rasping tongue. Damage may be jagged feeding along the edges of the leaf or in severe cases complete shredding. It is not uncommon to have a leaf or stem completely eaten through. Young slugs feed close to the center of the leaf and may damage just under the leaf surface.

Damage by slugs is most serious in damp areas or during extended rainy periods. The foliage and flowers of iris, gladioli and petunias are often damaged. Seedlings of both ornamental and vegetable crops may be severely damaged, enough that fields must be replanted. Tomato fruits on the lower parts of plants and also strawberries are often damaged.

Management

Sanitation

Slug populations can be reduced by eliminating their breeding and protective hiding places. Remove rotting boards, logs and other debris from the area. Destroy plant refuse and properly stack or store field boxes, sacks, etc. in a dry area. Cut and trim coarse grass and weeds along fences and ditches near susceptible crops. Compost leaves and other organic matter some distance form garden.

Traps

In small areas with light infestations such as gardens, place boards or other flat pieces of material at least 6 inches square at various locations. Each morning slugs beneath the "trap" may be killed by mashing, drowning in a bucket of salt water or oil, or putting salt on them.

Chemicals

NONE OF THE CHEMICALS LISTED BELOW SHOULD BE USED ON FOOD CROPS:

Dusts

In greenhouses and for other special areas, a 15% metaldehyde dust is available from greenhouse supply houses. Treat areas frequented by slugs two or more times at 10-day intervals. Follow label directions.

Baits

Baits are usually broadcast as flakes or pellets at a rate of about 1 pound per 1000 square feet. They may also be placed in piles throughout the infested area. If the pile method is used, be sure to place them at least 3 feet apart and beneath a board shingle, inverted flower pot or a similar item to prevent accidental poisoning of birds, dogs, and other small animals.

Most baits contain Sevin or metaldehyde. Water area to be treated and then scatter the bait lightly. So not get bait on foliage or contaminate food crops. Apply to slug hiding areas outside the garden.

Lime

Hydrated lime around field edges acts as a barrier.

Cryolite

Cryolite may be used as a dust or a spray on some crops. Check label closely and follow directions.

Beer

According to the USDA "you can partially control slugs if you place shallow dishes of beer in the vicinity of infested plants. Some species will crawl into the beer and drown. Adding molasses, corn meal or flour will enhance the attractiveness of beer.