Soybean producers in northeastern Oklahoma should be on the lookout for Japanese beetle infestations.
“Reports have been received of the beetles in double-crop soybeans in Ottawa County,” said Tom Royer, Oklahoma State University Cooperative Extension integrated pest management specialist.
Though not widely established, Japanese beetles have what seems to be a permanent presence in several counties located in northeastern Oklahoma, as well as the area around Ponca City in Kay County.
Adults are 1/2 inch-long, metallic green and bronze beetles. They have a row of five white tufts on the side of the body below the bronze wing covers and two white patches at the tip of the abdomen. The immature larvae stage manifests as white grubs.
The adult beetles begin to emerge in early June and feed for up to 60 days. A female beetle will say from 40 to 60 eggs in groups of one to eight into the soil.
“Larvae hatch in about two weeks and feed on plant roots and decaying material, continuing to mature before entering a state of hibernation in the late fall,” Royer said. “They finish development in the spring, pupate and emerge from the soil as adults.”
Adult Japanese beetles feed on more than 400 plant species. As the beetles feed, they eat the green material on a leaf and leave the leaf veins behind, resulting in leaves that resemble a lace-like leaf “skeleton”.
“While Japanese beetle feeding looks bad, soybeans can sustain substantial defoliation before they begin to suffer yield loss,” Royer said. “The amount of yield loss and treatment threshold depends on the growth stage of the plants.”
● For seedlings, the treatment threshold is 10 percent to 15 percent stand loss;
● For three-leaf plants to the beginning of bloom, the treatment threshold is 35 percent defoliation;
● For plants from bloom to pod fill, the treatment threshold is 15 percent to 20 percent defoliation; and
● For plants from pod fill to maturity, the treatment threshold is 35 percent to 40 percent defoliation.
Neither of OSU’s soybean publications lists control options for Japanese beetles because the pests have not been a problem until very recently. There are several insecticides registered for their control.
Royer and his fellow specialists checked the registrations suggested list for blister beetle control in OSU Division of Agricultural Science and Natural Resources Fact Sheet EPP-7167, “Soybean Insect Survey and Control In Oklahoma,” and E-832, “2011 OSU Extension Agents’ Handbook of Insect, Plant disease and Weed Control.”
“All insecticides listed for blister beetle control also are registered for control of Japanese beetles and should therefore be effective,” he said.