Japanese Beetles Appearing in Corn and Soybean Fields

Posted June 2019

SOURCE: NE Cropwatch

From article posted by Robert Wright - Extension Entomologist | Justin McMechan - Crop Protection and Cropping Systems Specialist

The Japanese beetle population has been growing over the past years in Nebraska.   They were originally spotted in the eastern border counties of Nebraska a few years ago. In 2016, the beetles were located near Lincoln county. They are starting to appear this year in eastern parts of the state and will continue to appear in the upcoming weeks. The main crops that they eat are corn and soybeans, as well as landscape trees and shrubs.

These beetles usually eat in groups because they are attracted to the female sex pheromone as well as volatile chemicals that damaged plants emit. They produce one generation annually.

Japanese beetles can cause defoliation with soybeans. They eat leaves entirely other than the leaf veins. Their damage is seen easily as they mainly eat in the upper canopy area of the crops.

Japanese beetles remove the green surface tissue of corn leaves prior to corn silks appearing. They will also feed on corn silks. The beetles may affect pollination if there are many of them. Over the silking period, treating with an insecticide is recommended if each ear has three or more Japanese beetles, the silks have been clipped to under 1/2 inch, and pollination is less than 50% finished.

To treat Japanese beetles, several different insecticides can be applied. Insecticides should be used with soybeans when insects are found and it is anticipated that defoliation damage will reach over 30%  in the vegetative state and 20% in the reproductive stage.

However, before treatment it is important to scout the entire field first as more Japanese beetles are found in field margins.

To spot a Japanese beetle, look for insects near 1/2 inch in length with a metallic green head and thorax. They have groups of white hair tufts on both sides of their abdomen. Japanese beetles look similar to the sand chafer. This insect is common in Nebraska, often located near Nebraska river valleys. These beetles are similar in size, but their color is coppery brown to black instead of metallic green.

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