When Farmers Should Spray for Japanese Beetles

Japanese beetles are showing up in corn and soybean fields. These can do enough damage to cause yield losses, but it is fairly unlikely. The University of Illinois has published thresholds for when farmers should spray crops to protect them from the Japanese beetle.

Nick Seiter says there needs to be a lot of beetles and a whole lot damage done before a producer should spend money on a rescue treatment, “Most of the reports that I am getting, as you would expect and as is typical, are below the treatment thresholds. These are 25 percent defoliation after bloom and 35 percent before bloom for soybean and the threshold for silk clipping in corn is consistent clipping to half-an-inch or less regularly throughout the field. I had a question yesterday about what to do when you have both Japanese beetles and corn rootworm clipping silks in the field. The answer is the same, the clipping has to be down to half-an-inch or less consistently through the field while pollination is still ongoing.”

ILLINOIS Extension Entomologist Nick Seiter says farmers have no need to apply a rescue treatment for Japanese beetles until defoliation reaches at least 25 percent after bloom for soybean and silk clipping during pollination is down to half-an-inch or less for corn.

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