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How to cut aphid angst

Agriculture.com Staff 07/14/2009 @ 9:56am

August used to be a time when soybean farmers could take a breather prior to harvest.

No more. The advent of soybean aphids infesting U.S. soybeans at this decade's start changed this.

Even so, farmers could let down their guard a bit due to the odd-year, even-year aphid cycle that developed. Typically, aphid infestations peaked in odd years like 2003 and plunged in even years like 2006.

No more.

Last year was certainly an exception (to lighter even-year infestations), especially in the Dakotas, Minnesota, Nebraska, Iowa, southern Wisconsin and northern Illinois, says Mike Gray, University of Illinois Extension entomologist. In some cases, he notes two to three insecticide applications were needed in some Upper Midwest fields.

Odds are farmers in some regions could be in for an anxious August.

"Aphids have to overwinter on buckthorn, a woody perennial found along streams, fence rows, and riparian areas," says Matt O'Neal, Iowa State University (ISU) Extension entomologist. "Last fall, we found more aphids on buckthorn than we had ever seen in Iowa."

Meanwhile, predators that prey on soybean aphids were not as prolific. "Eventually I saw predators, but their numbers were down," he says.

Several converging factors may account for aphids breaking the bi-yearly cycle. It's possible there were low numbers of predators in 2008, says Gray.

O'Neal adds that a cold and wet spring may have dented aphid predator levels like the Asian ladybird beetles and Orius insidiosus (pirate bugs). This, coupled with late emergence of aphids in many areas, prompted many aphids to dodge predators.

Low Orius populations in 2008 may reveal an ominous trend. "We may start to think about Orius as the canary in a coal mine," he says.

O'Neal is concerned that broad-spectrum insecticides aimed at aphids and other pests may also kill beneficial species that prey on aphids.

"This may be exacerbating aphids from being an off-and-on pest to being constant every year," says O’Neal.

August used to be a time when soybean farmers could take a breather prior to harvest.

If that's the case, soybean farmers have several tools to manage aphids. Insecticide-laced seed treatments can provide up to 65 days of protection for early-emerging aphids. These tools don't protect against outbreaks in the prime aphid season of late-July and August, though.

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