Plant Health Initiative

Bean Leaf Beetle - Agronomic Impact

Seedlings usually recover from insect damage, but soybean viruses can be transmitted by bean leaf beetle feeding at this stage. Photo credit: Marlin Rice, Iowa State University

Early feeding

Bean leaf beetles feed on young, new tissue and can cause noticeable defoliation on seedlings. Fortunately, feeding by first-generation beetles on soybean leaves seldom results in economic yield losses as seedlings can often recover. Recommendations developed at the University of Nebraska suggest a density of 16 adults per row foot in the early seedling stage before economic injury from physical feeding will occur. By the V2 stage, 39 beetles per row foot are required before economic injury will occur.

Transmission of viruses by first generation beetles

Transmission of soybean viruses is a separate issue. Early feeding by the overwintered and first-generation beetles in early (May) and mid-season (June-July) can cause the initial introduction and spread of Bean pod mottle virus into soybean fields.

Feeding by second-generation beetles can reduce yield and quality

Feeding by second-generation bean leaf beetles in August is not important in the spread of soybean viruses, but can cause significant damage to seed yield and quality. Complete pod loss can occur when adults feed at the base of the pod. This type of injury is referred to as "pod clipping." Feeding on the outer pod wall leads to pod lesions and seed damage.

Damage to pods by second-generation bean leaf beetles can lead to significant loss of yield and seed quality.

Damaged pods are predisposed to secondary infection by bacteria and fungi which may cause rotting and discoloration. Infections may increase in severity during periods of cool and wet weather.