Iowa soybean producers can certainly live without another soybean pest, but the Japanese beetle has already caused problems in eastern Iowa. During 2000, Virgil Schmitt, extension crops specialist, reported several fields southeast of Green Island in Jackson County that were sprayed because of heavy defoliation by this insect. This year, Virgil is seeing the beetles again in Clinton, Jackson, and Scott counties. Jim Fawcett, extension crops specialist, has found them in soybean east of Cedar Rapids in Linn County. No significant defoliation has been reported yet this summer, but field scouts should at least be alerted to the presence of this insect.
The Japanese beetle is an imported pest and is not native to Iowa. The adults have a metallic green head and pronotum (neck region) and reddish bronze wing covers with a row of white hair tufts along the abdomen. There is a single generation in the Midwest. Beetle feeding on soybean occurs from late June to early September, with the heaviest defoliation in July and August. This insect has been a significant pest in soybean in Indiana and Ohio for many years. There are no thresholds based on the number of beetles per plant or unit area. An economic threshold in reproductive-stage soybean is 20 percent defoliation.
This article originally appeared on page 173 of the IC-486(21) -- August 20, 2001 issue.