Fall Sampling Helps Assess Spring Slug Populations

October 22, 2002

WOOSTER, Ohio - For no-till growers with a history of slug problems, fall is the time to sample fields to help determine spring populations.

Ron Hammond, an Ohio State University entomologist with the Ohio Agricultural Research and Development Center, said fall slug sampling gives growers an idea of how severe slug populations may be in the spring and lends to appropriate management decisions.

"Fall is the time when growers can start getting an idea of what's out there in their fields. Research suggests that slug numbers in the spring tend to correlate with numbers found in the fall," said Hammond. "What sampling does is that it gives growers some idea that they might have a potential problem in the spring. Last fall we had a lot of slug activity, which suggested we would have had a lot of slugs in the spring, and that proved to be true in some areas of the state." Adult gray garden slugs are commonly found in the fall, looking for places to lay eggs or to overwinter and lay eggs in the spring. The juveniles that hatch out in the spring are in the destructive phase of their development, feeding on anything they can find including newly emerged corn and soybean plants. No-till fields tend to carry the highest slug populations because the residue provides a shelter for the adults, the eggs and the juveniles.

Hammond said that by setting traps following crop harvest and assessing slug populations over a period of several weeks, growers can identify which fields might need special attention in the spring.

"There are two types of traps growers can set. One is laying down 10 to 15 boards throughout a field. The boards provide the slugs shelter and they will congregate underneath them," said Hammond. "The other trap is digging holes throughout the field and placing cups of beer in the holes. The yeast and fermentation process of the beer attracts slugs. You can achieve the same thing by mixing yeast, sugar and water." Hammond said that growers who are consistently finding high slug populations should consider planting early, scouting those earmarked fields more closely and keeping a molluscicide application in mind.

"The first thing a grower should do is plant early so the plant has a chance to outgrow any slug damage. A grower should also consider a molluscicide treatment, especially in a soybean field, if high slug populations are present," said Hammond. "Slugs will tend to eat the soybean plants before they've even had a chance to get out of the ground." Growers may also want to consider strip-tilling fields in the fall. Hammond said that although no evidence exists to suggest strip tillage reduces slug populations, the practice help plants germinate more quickly and grow faster which helps to outgrow slug damage.

"Strip tillage, however, is a practice usually used by corn growers. Soybean growers don't generally practice strip tillage and soybeans fields can be the ones hardest hit," said Hammond. "But even for corn growers, every little bit of slug control helps." Hammond said that even if growers are not finding high slug populations in the fall, it's always a good idea to scout fields in the spring, especially if growers have had slug problems in the past.

Hammond and his colleagues have begun sampling fields to determine spring slug populations. "There is some indication that the slugs survived fairly well this summer despite the significant drought we had," he said. "But we'll be able to make more of an assessment in the coming weeks once harvest is completed."

Author(s): 
Candace Pollock
Source(s): 
Ron Hammond