Figure 1: Bean leaf beetle adults.
Figure 1: Bean leaf beetle adults.

The bean leaf beetle (BLB) overwinters in the adult stage, and resumes activity in the spring. It will be found feeding on soybean foliage soon after soybean emergence. The overwintering BLB adults feed on foliage and deposit their eggs in the soil.

If a soybean field is planted late relative to other fields in the area, the first generation may not become established in the field and the probability of early season BLB damage is minimal. However, if planted late and missing the first generation, the likelihood of the field staying green in September enhances the chance of having a higher second BLB generation.

The BLB larval stage feeds on the root system, and after a few weeks the larvae pupate and adults emerge to feed on the soybean foliage. The current thought is that significant injury to roots by larval feeding does not occur. Bean leaf beetle passes through two generations in Ohio with the first generation of BLB beetles appearing in early summer and the second generation appearing around late August or early September.

The time of peak occurrence of BLB adults per generation may differ from field to field depending on the date of planting because the time of initial egg laying in a field depends on the time of initial emergence of the crop, which attracts the overwintering beetles to the site.

Late-planted fields in which the overwintering generation does not develop may be colonized later by migrating first or second generation adults. Because these fields often remain green into mid- September to late September, they often serve as a trap crop for second generation adults migrating from other fields that were planted early and are maturing. This sudden increase in second generation beetles may cause significant pod injury.

A secondary concern with BLB is its ability to vector bean pod mottle virus (BPMV). Infection by this virus results in plants that remain green well past harvest maturity, with seeds that often are severely mottled. The concern with seed quality is especially important when soybean is grown for seed or for food-grade soybean. Initial spread is by the overwintering BLB population followed by secondary spread by first generation adults.