Landscape and Greenhouse - Slugs

Slugs can be a major problem in greenhouses and in the landscape in the spring. The following is a short article on the subject.

There is no sure-fire solution to slug problems in landscape plantings and gardens during early spring. Slugs are favored by cool, wet weather and can remain active until hot, dry conditions force them into protected sites. Slugs feed on a wide variety of plants, shredding the leaves with their rasping mouthparts. They can be especially damaging to newly-set transplants and bedding plants.

In general, insecticides have little effect on slugs and chemical control is limited to applications of baits containing metaldehyde or metaldehyde + carbaryl (Sevin) as the active ingredient(s). The bait needs to be scattered evenly over the ground so that slugs encounter the pellets as they slide along in search of food. Baits disintegrate following rain or heavy dew so additional applications may be necessary. Also, metaldehyde is broken down by sunlight so it is relatively short-lived. Spreading the bait late in the day, rather than early in the morning, will help to get in front of the slugs with minimal loss.

Slug baits containing iron phosphate are also available. This active ingredient is available under several brand names in products that provide safe, effective slug control. Iron phosphate baits provide a good margin of safety where children, pets, or wildlife are a concern.

Sprinkle any baits where slugs, or their slime trails are seen regularly and retreat the same spots during slug season. Slugs tend to remain near food sources so you may get some advantage by providing a dependable temptation for them. Scatter baits evenly instead of small piles. This increases chances of consumption by slugs and reduces the chances of the bait being eaten by non-target organisms. The product label will give information on application rates and other suggestions for improving control. Baits can be an effective part of slug management but it is difficult to control them with these products alone.

Slugs will move under shelter during bright sunny days or when the humidity is low. Removing hiding places, such as boards, rocks, etc. will force them to find other shelter and perhaps relocate and do less feeding in the area. Also, hiding places can be used against them. Pieces of moist cardboard, rolled-up newspaper, boards, or upturned flower pots can be left on the ground in a few spots. Slugs will tend to accumulate under the shelter and can be scooped up and discarded. It is good to have these items propped about 1" above the ground so that the slugs can get under them easily. Keep the shelters in place during "slug season". This approach is most successful when there are not many other hiding spots and weather conditions cause the slugs to seek shelter.

Beer traps will collect many slugs because they are attracted to fermentation odors and drown in the liquid. Adjusting the trap so the rim is about one-half inch above the soil line will reduce the number of ground beetles and other non-target creatures from being caught. Fill the container about half-full and replace the contents every few days. Sugar water with some yeast can be used in place of beer.

Barriers can provide some relief if the slugs are moving in from outside the area that is being protected. Wood ash or fine lime can be used but both lose their effectiveness when wet and too much wood ash is not good for the soil. Slugs do not like to cross copper. A copper barrier tape (about 1" wide) can be used along borders or around the legs of greenhouse tables to deter slugs. There are wider copper barriers that can be set in the soil as fences but the expense makes this most suitable for small areas.

Reprinted from "Slugs" By Lee Townsend in the March 20, 2006 edition of the Kentucky Pest News from the University of Kentucky, College of Agriculture.