When you’re out scouting your fields this summer, look for a small beetle with a shiny copper-colored body and a green head and thorax. These little pests are Japanese beetles, and they’re making their way across the Midwest.
Japanese beetles can usually be found feeding on gardens, trees and shrubs, but they’re also known to pop up in corn and soybean fields. My region in Illinois has an increased infestation of Japanese beetles this year earlier than ever, causing concern for area corn and soybean growers who worry how the pests will affect yield. Here are a few things you should know about Japanese beetles and how you can treat your fields this year:
- Japanese beetles are in the order Coleoptera and the family Scarabaeidae. The beetles start as eggs and hatch into larvae in the soil during the winter. As larvae, they moult to become C-shaped grubs. As temperatures rise in the spring, the grubs break hibernation and within four to six weeks pupate into adults.
- Where there’s one Japanese beetle, there may be hordes of beetles nearby. Japanese beetles do not travel alone as they feed in clusters. This is a result of a pheromone the beetles emit that attracts other beetles as they feed on the leaves of plants.
- They typically pop up around late spring/early summer. Check corn silks and leaves for signs of the insect, as well as the leaves and flowers in soybean fields. The beetles feed on these parts of the plant, which can ultimately affect pollination and yield.
- If you don’t immediately see the beetles, their damage can often times be detected on the plant. Silk “clipping” can be spotted on corn plants, and holes in leaves or shredded (or defoliated) leaves with brown edges can be signs of the pests. In soybeans, Japanese beetles typically feed on the leaf tissue between veins, which leaves behind a lace-like skeletonized appearance.
- If Japanese Beetles are detected, they can be controlled through insecticides such as Sevin or pyrethroid insecticides.
- The University of Illinois Department of Crop Sciences notes that the threshold of Japanese beetles in soybeans should be based on the percentage of leaf defoliation. The university recommends that treatment should be considered if 20 percent of the leaf is defoliated before bloom and pod fill and if pre-bloom soybeans have around 30 percent leaf defoliation.
- In corn, the university recommends that insecticide treatments should be considered if silks on the plant have been clipped to half an inch or less or if pollination is less than 50 percent complete. The university also recommends treatment if more than three beetles can be found per ear.
For more information on Japanese beetles and how to detect and prevent these insects from robbing yield, contact your local Stine sales rep.