Bean Leaf Beetles: Early Season Soybean Defoliators In 2017

 

 

The overwintering generation of bean leaf beetles are currently very active in soybean in Southern South Dakota. Many of the observed populations are now exceeding the thresholds for beetles per plant and also defoliation. During the early stages, estimating defoliation on soybean leaves can be difficult so counting the number of beetles present can be more effective to evaluate populations. In addition to feeding on soybean leaves, bean leaf beetle also vectors bean pod mottle virus.

 

 

Adult bean leaf beetles are ~1/4 inch long and vary in color from yellow, brown to red with the potential for many variations of those colors to occur (Figure 1 and Figure 2). Adult beetles have a black triangle directly behind their thorax. Additionally, beetles can have 0, 2, or 4 black spots on their backs.

 

 

 

Overwintering bean leaf beetles feed on soybean cotyledons, stems, unifoliate leaves, and emerging trifoliates (Figure 3 and Figure 4). Stand loss is possible when overwintering bean leaf beetles arrive in soybean fields at or during plant emergence and destroy the growing point.

 

 

 

 

Scouting for overwintering bean leaf beetles can be difficult because adult beetles readily drop off plants when disturbed by wind, shadows, or movement. To monitor fields for bean leaf beetles, search five areas throughout a field for beetles, making note of the number of beetles per plant. Try to avoid casting a shadow over the scouted plants as this will cause the adult beetles to drop off plant. Economic thresholds for VC and V1 soybean are listed in Table 1.