Tuesday, May 12, 2009

Landscape and Greenhouse - Slug Season

This past week has been ideal for slugs. The following is a good article on the subject.

Slugs are almost universal pests in vegetable gardens, shade gardens, and shaded landscape areas. Their soft, unsegmented bodies, exude a slimy, mucous-like substance that leaves characteristically shiny trails as they move from hiding to feeding spots. Once on a plant, slugs use their rasping mouthparts to scrape away at the leaf tissue. Immature slugs tend to feed on surface tissue while larger individuals eat rounded holes completely through the leaf. Slugs usually feed at night and hide in moist, dark areas during the day. They may eat several times their own body weight each night so serious damage can occur in a very short time. Disappearance of seedlings or newly set transplants is often blamed on cutworms but slime trails are a key clue in incriminating slugs.

Slugs prefer temperatures in the low 60's but can lay eggs and develop normally down to about 40 F. They can survive slight freezing but tend to hide in cracks and crevices when cold weather threatens them. Usually, warm temperatures are the concern. Slugs try to avoid temperatures above 70. Rising temperatures spur them to crawl down to their hiding places to rest and absorb water through their skin. As temperatures start to fall, slugs actively begin foraging, again. Slugs are so sensitive to temperature that they can detect changes as gradual as 2 F per hour!

Slugs are very sensitive to air currents. Gentle breezes cause them to turn toward the source and extend their antennae. As the breeze becomes stronger, they turn away from the source, evidently to escape dehydration. Improved ventilation of a trouble spot may make it drafty and force slugs to move. Good sanitation, including removal of extraneous vegetation, excess mulch, or other materials that might offer food or shelter, will aid in the overall control program.

Slug baits containing metaldehyde or iron phosphate may be used for control. Best results are usually obtained if the baits are applied in the afternoon watering is delayed until the next day. Slugs feed intermittently so several applications of bait may be needed for control. Baits may attract slugs from up to 3 feet away. Beer-baited traps will lure in many slugs but is it important to check and empty the traps regularly. Pieces of wood, cardboard, or other objects can be placed on the ground in infested areas to provide hiding sites for foraging slugs. Regular visits to the slug accumulators will allow you to collect and discard the resting slugs.

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.

Information from Lee Townsend, University of Kentucky.

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