MU Confirms Japanese Beetle Emergence in Corn and Soybeans

By Blake Jackson

The University of Missouri’s Pest Monitoring Network has confirmed the first Japanese beetle captures of the 2026 season, signaling the start of adult beetle emergence and prompting farmers to monitor soybean and corn fields for potential damage.

“Although trap captures are currently low, these first detections indicate that Japanese beetles are beginning to emerge,” said 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,” continued Valmorbida.

Japanese beetles, an invasive insect species in the United States, complete one generation each year in Missouri and feed on a wide range of plants, including soybeans and corn.

According to Valmorbida, beetle activity is expected to peak over the next two to four weeks.

In soybean fields, adult beetles feed mainly on leaves in the upper canopy, creating a skeletonized appearance by consuming leaf tissue while leaving the veins behind.

Growers are encouraged to inspect multiple areas of each field and estimate defoliation across the entire plant canopy before making treatment decisions.

Foliar insecticides are generally recommended if defoliation is expected to exceed 30% before bloom or 15% during reproductive growth stages.

In corn, beetles feed on silks during pollination, and excessive silk clipping can reduce kernel development and yields.

Treatment may be justified when there are at least three beetles per ear, silks have been clipped to less than half an inch, and pollination is less than 50% complete.

FAQs:

• Why are Japanese beetles a concern for farmers?
  They can damage soybean leaves and corn silks, reducing crop yields.
• When do Japanese beetles usually peak in Missouri?
  Peak activity typically occurs within two to four weeks after initial emergence.
• How do Japanese beetles damage soybeans?
  They skeletonize leaves by feeding leaf tissue while leaving veins intact.
• When should soybean growers consider insecticide treatment?
  Treatment is recommended when defoliation exceeds economic thresholds based on growth stage.
• How can Japanese beetles affect corn production?
  Heavy silk feeding can interfere with pollination and reduce kernel set.

Photo Credit: lvair-valmorbida