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College of Food, Agricultural, and Environmental Sciences


Size Matters with Slug Feeding

January 31, 2006

WOOSTER, Ohio -- The first signs of slug activity and feeding in crop fields is correlated with the size of the juveniles, according to Ohio State University entomology research.


Field studies conducted last summer at the Ohio Agricultural Research and Development Center in Wooster, Ohio, revealed that slugs reach a certain size before they begin to feed. Up to that time, slugs are generally inactive. The results may help to predict more precisely when slugs become a problem throughout parts of Ohio, and could help to improve management practices.

"We are getting a feel for exactly when the eggs will hatch and when slugs will begin feeding," said Ron Hammond, an OARDC research entomologist. "We found that slugs really don't do much damage until about two to two and a half weeks after hatching. When they get to be anywhere from 2 milligrams to 8 milligrams in size, then they start becoming active. We also know that the further south you go in Ohio, the earlier the juveniles will reach that feeding size."

Knowing how soon after hatching slugs will begin feeding through parts of Ohio reinforces the most important aspect of slug management: The earlier the crop is planted, the better its chances are for outgrowing any slug damage.

"If we are following the size of the juveniles and when we should start to see feeding, we can better relate that to how well the crop is growing. In times of good weather, the crop could potentially outgrow any slug damage," said Hammond. "On the other hand, if the crop is planted late, at or around the time those juveniles hit that size for feeding, then the crop could be in a lot more trouble."

The juvenile stage of the slug creates the most damage to crops and its voracious appetite and large densities can be devastating for farmers who have had a history of slug problems. Upon hatching in early to mid-May, the slug will begin feeding on anything that is planted in the field, whether it's corn, soybeans or alfalfa. Slug feeding can cause significant reductions in corn yields and total stand loss in soybeans.

Slugs are most problematic in no-till fields. Tillage tends to bury eggs deep in the soil, thereby helping to keep slug populations low. Such a scenario does not exist in no-till, where the idea is to leave soil residue undisturbed for added production benefits and to keep soil erosion at a minimum.

The one thing growers can do to help control slug damage is to scout their fields on a regular basis.

"The slug situation this season will be like that in years' past. Fall sampling uncovered a lot of adult slugs, so the potential will be there for high slug populations," said Hammond. "As always, severity will be dependent upon planting conditions, so growers still need to get out in their fields and scout for eggs and juveniles when the time comes."


Candace Pollock
Ron Hammond