Soybean Aphids Showing Resistance to Insecticide

The University of Minnesota has been looking into a class of insecticide to which aphids appear to be developing resistance. Last season, growers in southern Minnesota and at U of M Extension experiment stations found that their foliar insecticides weren’t working to control aphids.

Lab tests confirmed that aphids were developing resistance to pyrethroids.

Problems developing in Minnesota eventually could mean issues for surrounding states as aphids move, said Adam Varenhorst, crop entomologist for South Dakota State University Extension.

“They kind of are the hot spot for soybean aphids in the Midwest. A lot of other states’ populations originate there,” he said.

For that reason, Varenhorst and other researchers will be keeping an eye on aphids in their areas. Soon, they’ll be visiting fields to test aphids for resistance. He expects early infestations will come from local populations of aphids, but later in the season, there’s risk that the resistant Minnesota aphids could move in.

“It’s possible they might show up,” he said.

Resistance to pyrethroids is a big problem, he said, especially given the other classes of insecticides that recently were taken off the market.

Last year, the Ninth Circuit Court of Appeals, which covers the western U.S., revoked the license for Sulfoxaflor because of evidence that it is harmful to pollinators. Other insecticides are currently under scrutiny, including organophosphates and neonicatnoids.

“We’re getting down to the line on what we have to manage them,” Varenhorst said.

“The grower is basically losing a tool,” added Elijah Meck, technical product lead for Syngenta in Greensboro, N.C.

Developing new modes of action takes a significant amount of resources and time, he said. “It’s not something that’s easily replaced.”

Syngenta and other companies are part of an Insecticide Resistance Action Committee that helps growers manage resistance issues.

The U of M pest management team has suggestions for keeping pests from becoming resistant to chemical control. They suggest that growers use multiple methods of managing problem insects, including planting pest-resistant varieties, encouraging biological control and rotating crops.

Growers should use insecticides only when necessary, scouting regularly to see whether pests number more than 250 per plant. Applying insecticides in strict accordance with the label directions is important as well.

Lastly, using different types of insecticides can keep pests from developing resistance to one class such as pyrethroids.

U of M staff will be following up on resistance issues, testing aphids from fields around the state to see if traits for resistance was passed on to this year’s aphids. One test at the Southwest Research Station at Lamberton, Minn., so far found no resistance, according to Bob Koch, U of M Extension entomologist.

“That’s a good sign for going into 2016,” he said.

Source: Janelle Atyeo, Tri-State Neighbor 

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