Bean Leaf Beetle Distribution and Biology
• Injury, which includes leaf defoliation and pod scarring, can have a significant impact on soybean growth and development. Large populations of bean leaf beetles can cause defoliation of seedlings.
• The bean leaf beetle can transmit bean pod mottle virus to soybeans by feeding on the leaves.
• Soybean pods that have been damaged by the bean leaf beetle can also serve as an entry point for fungal pathogens, which can affect seed yield and quality.
• The feeding period of the bean leaf beetle is 21 days or longer if there are multiple generations of beetles in one season.
• Adult bean leaf beetles overwinter in wooded lots next to soybean fields. They emerge in the spring and become active around 50-55 degrees Fahrenheit.
• The number of generations produced by the bean leaf beetle in one season is determined by latitude. The Southeast United States typically sees three generations, while the Midwest usually has one or two generations.
Insecticide Resistance in Bean Leaf Beetle
Resistance to pyrethroid insecticides (Group 3) has been documented in the mid-South and North Carolina.
Management of Bean Leaf Beetle in Soybeans
Getting out into the field to scout for infestations of the bean leaf beetle is the best way to determine the right time for application of foliar insecticides.
• Scout for infestation levels. Examine at least five plants from five areas of the field to estimate the percentage of defoliation. Inspect all pods within 2 linear feet of the row from multiple locations in the field to estimate the percentage of pod damage.
• Be mindful of thresholds. Only make insecticide applications after thresholds are met. The economic threshold during the preflowering stage is when defoliation exceeds 30%. The threshold is met during the pod-forming and pod-filling stages when defoliation exceeds 20%. Adult bean leaf beetles cause damage by feeding on the leaves and scarring and clipping soybean pods when soybean plants are most susceptible to damage (R4-R6). For pod feeding, treat at 5-10% of pods with feeding injury. These recommendations are likely to vary by state, especially in areas at risk for transmission of bean pod mottle virus.