Japanese beetles arrive in large numbers

Wednesday, August 20, 2014

Beetles feed on corn, soybean crops, can prevent pollination

Japanese beetles have been reported in large numbers across the state this year.

Trap counts through Missouri indicate the beetle population will continue to climb, and should be peaking this month. The beetles are said to feed on any plant that has an appealing aroma to them, making them a threat to farmers in Barry County.

Trap counts monitoring the Southwest Region trapped a little over 5,300 beetles in a span of 5 days in July.

According to Sarah Kenyon, agronomy specialist with the University of Missouri Extension, the insects feed on roses, shrubs, vegetables and field crops such as corn and soybean.

These corn and soybean field crops can suffer serious damage if precautionary control measures aren't taken. The beetles will chew on corn silk and tassels, and if the silks are taken down to any less than half an inch in length, there won't be any pollination. This will result in poor production of corn.

Insecticidal treatment of corn field crops is recommended when there are three or more beetles per ear that are producing green silks and if pollination is less than 50 percent complete.

As for soybean crops, the beetles chew at the leaves. Damage control in the form of insecticidal treatment is justified if there is 25 percent damage to the soybean leaves.

"The damaged leaves typically look like swiss cheese," Kenyon said.

The damage of adult Japanese beetles feeding is usually observed as a lace-like pattern of defoliation because the beetles tend to avoid leaf veins when feeding, according to Wayne Bailey, MU entomologist.

Bailey says that roses and linden trees are their favorite crops, but they'll feed on a wide variety.

"They'll feed on a wide variety of ornamentals, fruit trees, grapes and 440 different plant species," he said. "They usually feed on the tops of plants in the sunlight and they like plants that smell succulent.

"So, if it smells good to you they likely will prefer those plants."

Japanese beetles are around a half an inch in length and are usually metallic green in color with copper or bronze colored wings. According to a statement written by Bailey on the MU Integrated Pest Management website, a diagnostic characteristic is the twelve white tufts of hair (or bristles) present around the edge of the shell. These appear as white dots on the beetle without magnification.

Adult beetles emerge from the soil in early June and mate and feed for approximately 45 to 60 days. Each female beetle usually lays around 40 to 60 eggs into the soil with the larvae emerging within two weeks. These will feed on plant roots and decaying material and then stay in the soil through the winter.

In the spring, the larvae will finish development, pupate, and emerge as adult beetles in early June the following year, according to Bailey.

For corn and soybean field crop farmers, there is a list of recommended insecticides for control of Japanese beetles in Barry County at imp.missouri.edu. People can also monitor the trap counts on the website.

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