With the cooler fall temperatures, slugs seem to be feeding incessantly, attacking newly planted cover crops and fall-planted small grains, says John Tooker, Penn State University entomologist.
"Slugs, of course, are most often problematic in no-till systems and thrive in high-moisture, high-residue fields," Tooker says.
Unfortunately for farmers with slug problems this fall, Tooker says many management tactics need to be implemented in spring, but there are few options that farmers can implement this fall that stand a good chance of reducing slug populations next spring.
Most slugs have a single generation per year with overwintering eggs hatching in spring and slugs developing through spring, summer and fall, Toker says. As winter approaches, slugs lay eggs, which overwinter and hatch the next spring.
He says anecdotal evidence of apparent full-size slugs seen early in the spring seems to suggest that some adults can survive until next spring and resume feeding.
"To assess slug populations this fall, it's necessary to scout fields," Tooker says. "Because slugs are most active at night, this can be done easily by placing wooden boards in fields, such as siding or even roofing shingles of some standardized size.
"Slugs will hide under these boards during the day providing an opportunity to gauge population size."
Tooker suggests leaving the boards in place for a few day and counting slugs. Then, keep track of which fields have the largest populations and then in the spring, scout these fields first for damage.
"There is a good chance that high fall populations will lead to high spring populations and a need for chemical control," Tooker says.
Another tactic that may be of use is removing debris from fields. Some folks that do not use cover crops remove stubble for bedding.
"These more-exposed fields would tend to dry out more quickly, which would leave them less likely to harbor damaging slug populations," Tooker says. "This tactic, of course, would not be available to farmers regularly using cover crops."
Another tactic that has anecdotal support for helping to decrease slug populations is incorporating some degree of fall tillage. Tooker says shallow discing or turbo tillage provides some incorporation that should help knock back slug populations in the spring.
"A grower looking to test this option could easily leave a portion of the field untreated to see if the management was effective," he says.
If slug problems are particularly bad, growers might consider fall applications of metaldehyde baits. Tooker says such applications can be effective, but are not the most efficient use of these baits. Some adult slugs may have already laid eggs; the chemical treatment might not contribute too much to reducing spring populations.
Tooker adds that in the struggle against slugs, natural enemies have a lot of potential to contribute to slug suppression. Some ground beetle and harvestman (aka daddy long legs) species are voracious slug predators; unfortunately, natural enemies populations in many crop fields never get a chance to build because of regular use of broadcast insecticides.
"Many growers tankmix insecticides in the spring as an insurance policy against other potential crop pests," Tooker says. "But it should be recognized that applications of insecticides in absence of crop damage are economically dubious and have the potential to disrupt often unrecognized natural enemy-provided control.
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