Bean leaf beetle is a pest of soybean in most soybean growing regions of the United States. There may be three generations in the southern U.S., two generations in the central Corn Belt (Nebraska, Iowa, Illinois), and only one generation in the northern Corn Belt.
Adults feed on cotyledons, leaves, and the external surface of pods. Larvae feed underground on nodules and roots.
Adult bean leaf beetles also can transmit a soybean pathogen—bean pod mottle virus—which causes “stay green” and delays soybean maturity.
Following mild winters, which contribute to higher than average survival, bean leaf beetle populations can reduce plant populations by feeding on newly-emerging soybeans, especially in early-planted fields.
During vegetative growth from the V2 stage to flowering, soybeans can tolerate from 40% to 60% defoliation without yield loss. Bean leaf beetles rarely, if ever, cause this degree of defoliation.
Second-generation beetles usually peak during soybean pod-fill stages, resulting in injured pods. Yield loss can occur at this time (usually during August in Midwestern states).
Scouting regularly for bean leaf beetle and spraying, if necessary, is recommended to address this problem insect. A new strategy to treat second generation beetles based on first generation beetle numbers has been proposed.