Japanese Beetles Found in Missouri

University of Missouri’s Pest Monitoring Network is reporting the first Japanese beetle captures of 2026 and calling for growers to begin scouting soybean and corn crops.

“Although trap captures are currently low, these first detections indicate that Japanese beetles are beginning to emerge,” says MU Extension state crops entomologist Ivair Valmorbida. “Economic damage is unlikely at this time, but farmers should begin scouting soybean and corn fields and monitor populations closely so they can determine whether a foliar insecticide treatment is warranted.”

The Japanese beetle (Popillia japonica Newman) is an invasive species in the United States. This species has one generation per year in Missouri, and adults feed on several plant species, including soybeans and corn.

Valmorbida says peak occurrence likely will happen in the next two to four weeks.

Adult Japanese beetles feed on soybean leaves, defoliating the plants. Adults feed primarily on the upper canopy, skeletonizing leaves by consuming leaf tissue and leaving veins intact.

To scout soybeans, estimate the percentage of defoliation at several locations across the field. Because Japanese beetles usually feed on the upper leaves, it is important to estimate defoliation throughout the entire plant canopy, Valmorbida says.

In soybeans, insecticide treatment decisions are based on growth stage and percentage of defoliation, including injury from other defoliators.

Foliar insecticide treatment is recommended when defoliation is expected to exceed 30% before bloom (V1-R2 growth stages), 15% during reproductive growth stages.

In corn, adult Japanese beetles feed on silks during the pollination period. Severe silk clipping may interfere with pollination, resulting in reduced kernel set and potential yield loss, says Valmorbida

Valmorbida says foliar insecticide application is warranted in corn crops if three conditions are met:

There is an average of three or more beetles per ear.

Silks have been clipped to less than half an inch.

Pollination is less than 50% complete.

The Pest Monitoring Network, part of the MU Integrated Pest Management program, offers an alert system for Japanese beetles and other pests. Subscribe to alerts at ipm@missouri.edu.

 

First reports of Japanese Beetles Received in Missouri

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.

 

Japanese beetles rear their shiny heads again on flowers and in fields

Farmers, gardeners and homeowners should keep their eyes peeled for shiny, green and bronze Japanese beetles feeding on the crops, vegetables and flowers.

 

This insect’s wide variety of food preferences make scouting a necessity.

 

“Certainly we need to be looking at this point,” said Wayne Bailey, a state entomologist for University of Missouri Extension. “These beetles are gregarious feeders, so if you have one, a lot will come in because they tell others through chemical signals that the food is good in an area. You might have a few in your garden the first year, the next year it might be in the hundreds and then the year after it could be in the thousands.”

 

Dry weather this year has affected the emergence of mature beetles. While some areas saw Japanese beetles first emerge as early as May, many are seeing populations peak in the last weeks of June.

 

“Japanese beetles first emerged about three weeks early this year because the warm winter allowed the white grub to emerge earlier,” Bailey said. “In a normal year we’d be having numbers similar to last year, but with this drought we’re not sure if numbers will be similar, higher or lower, but some of our traps are catching substantial numbers.”

 

The dime-sized green beetle – with bronze wings and white tufts of hair around its shell – feeds on any plant that has a pleasant smell.

 

“They do eat about 440 different plants, but their favorites include Linden trees and roses,” Bailey said. “They feed high in the plant, out in the sunlight, and can do a lot of damage to trees and ornamentals and shrubs.”

 

Japanese beetles also can feed on soybean leaves and corn silks, especially in the critical pollination period.

 

“In corn the economic threshold is three or more insects per ear when pollination is less than 50 percent complete and silks are chewed to less than a half inch from the ear husk, but sometimes you will get 20-30 or more beetles feeding on one ear,” Bailey said. “In soybean the threshold is set at 20 percent defoliation this year because of higher soybean prices.”

 

Japanese beetles arrived in the United States in the early 1900s, probably in potted irises from their native Japan. They were first found in New Jersey in 1916 and by 1932 had spread to Missouri, where they caused problems with ornamental plants and other crops.

 

About 10 years ago MU entomologists began seeing Japanese beetles in more rural areas of the state and they are now found in most counties. The insect can fly up to three miles to find a tasty, fragrant meal.

 

Japanese beetles live for one year. In July, the adults lay eggs, which hatch and develop into white larvae that overwinter in the soil and mature during the spring. They emerge as beetles around mid-June and begin feeding. Each healthy female lays 40 to 60 eggs. Adults live up to 60 days.

 

Homeowners can fall back on a staple insecticide, powdered Sevin (carbaryl), to combat Japanese beetles, or just pick the beetles off the plant.

 

“One of the things we discourage is putting out pheromone traps because they will bring in more beetles to your area than what would normally be there, and that can build your numbers faster,” Bailey said. “These beetles typically can move about three miles per year, and it’s very common in an area where you don’t have very many to see numbers climb exponentially from year to year.”

 

Find current insect numbers in your region from the University of Missouri at http://ipm.missouri.edu/pestmonitoring/jb/.

 

Read more about Japanese beetles and find pesticide recommendations at http://ipm.missouri.edu/IPCM/2012/6/Japanese-Beetle-Adults-Emerge-Across-Missouri.