Don't Feed Your Crop to Japanese Beetles

Jul 21, 2020

Japanese Beetles are feeding in corn and soybean fields. Feeding can impact pollination and reduce yield. Adult beetles are approximately 1/2 inch long, have a metallic green head, reddish to bronze wing covers, and six bunches of white bristles along the sides of their abdomen. 

Life Cycle

In late June, adults emerge and begin feeding on corn, soybeans, and other host plants, eventually moving up the plant to further feed and mate. In August and September, mated females eventually move back to grass areas and lay their eggs in the soil. Eggs hatch in the fall, and grubs feed on plant roots until soil temperatures cool. The grubs become active again in the spring when temperatures rise above 50F, continue feeding, and eventually turn into pupae and emerge from the soil as adult beetles. 

Plant Injury 

Japanese beetles can feed on corn leaves and silks, creating issues with pollination. Adults can also feed on soybean leaves and pods, and many other plant species. The treatment threshold for Japanese beetle feeding in soybeans is 30% defoliation before bloom and 20% defoliation after bloom. For corn, treatment should be considered if (1) there are three or more beetles per ear, (2) silks have been clipped to less than 1/2 inch, and (3) pollination is less than 50% complete. Silk clipping after pollination is complete does not affect kernel set. Since beetle pressure can be heavier hear field edges, scout multiple areas within a field to better estimate beetle population and percent defoliation. 


Communications Department

Filed Under: AgronomyCrop Protection