First reports of Japanese beetles received in four Missouri counties

COLUMBIA, Mo. — University of Missouri Integrated Pest Management reports the capture of its first Japanese beetles of the season, says MU Extension crops entomologist Ivair Valmorbida.

The beetles appeared in Stoddard, Barton, Christian and Holt counties, as reported by MU’s Pest Monitoring Network, which gathers information from across the state.

Since Japanese beetles are highly mobile, Valmorbida advises corn and soybean growers to begin scouting fields.

Adult Japanese beetles mainly feed on the upper canopy leaves, causing defoliation in soybean. Leaves become skeletonized with veins still intact.

Insecticide treatments for soybean are based on growth stage and amount of defoliation, including injury from other defoliators, because it is difficult to distinguish among types of feeding injury.

Foliar insecticides are recommended when defoliation is expected to exceed 30% before bloom (V1-R2 growth stages), 10% from pod development to pod fill (R3-R5) and 15% at the R6 (full seed) growth stage.

Japanese beetles are also considered a pest in corn crops. They can clip corn silks necessary for pollination, which can lead to some yield reductions, says Valmorbida. He says foliar insecticide application is warranted in corn if three conditions are met:

• There’s an average of three or more beetles per ear.
• Silks have been clipped to less than 0.5 inch.
• Pollination is less than 50% complete.

MU Extension’s pest monitoring website offers an alert system for Japanese beetles and other pests. Subscribe to alerts at https://ipm.missouri.edu or email ipm@missouri.edu.

Valmorbida recommends these publications:

• “Biology and Management of Japanese Beetle,” MU Extension, https://extension.missouri.edu/publications/g7412.
• Biology and Management of Japanese Beetle in Corn and Soybean,” Journal of Integrated Pest Management, https://academic.oup.com/jipm/article/10/1/9/954734.