Bean Leaf Beetles in Soybeans

Bean leaf beetles are small beetles that have a black triangle on their wings behind their head. They range in color from red to light brown. Often they will have a black checked board pattern, but not always – they will have the black triangle though. They are often confused with cucumber beetles, but cucumber beetles have a heart-shaped marking on their wings.

Bean leaf beetle adult. Notice the black triangle on its back behind the "neck".

Spotted cucumber beetle adult. Notice the upside-down heart-shaped marking on its back behind the "neck".

Bean leaf beetles come out from overwintering and begin feeding on soybean foliage soon after the soybeans emerge. Adults lay eggs into the soil. After larvae hatch, they feed on the root system of soybean plants. If your field is planted relatively late in comparison with the fields around your area, you may miss out on the first generation of bean leaf beetles. An insecticide seed treatment can provide protection against early season bean leaf beetle damage. But, if you didn’t use a seed treatment for protection, you can take care of them with a foliar application. A foliar application should be targeted once defoliation reaches 30% on pre-flowering beans. Since bean leaf beetles are season long pests, it is important to mention that early season control doesn’t mean that you won’t have problems with them later in the season.

Categories: Insects, Monitoring, Scouting issues, soybeans

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