In the last week, I have received several calls reporting heavy defoliation, pod feeding and high abundance of bean leaf beetles (BLB’s) in soybeans. The reports that I received are not widely spread but mostly concentrated in a defined geography. The fields we visited were in the R5-R6 stage with some showing defoliation levels as high as 60% and pod damage averaging 30%. Another field averaged 20% defoliation, and 8% pod feeding in the “good” spots, while a large patch of heavily damaged soybeans laid in the middle of the field (Image 1). Initially we thought these were spots affected by drought or early season pathogens but when examined closely, these were areas where defoliation and pod damage were well above thresholds (Image 2) and BLB numbers were high. Some spots had 4-7 beetles per plant, and they were actively feeding on tissue or pods. Most of the pod feeding was present in the upper portions of the plant, while mid to lower pods had little to no feeding. Because of the time left for these beans to mature and the significant BLB activity still present, a spray was recommended to protect the pods from any further damage. In general, when we are around a 10% pod feeding while pods are still green and beetles are present and actively feeding, an application may be justified. Keep in mind that past the R5-R6 stage the main focus of insect scouting should be to protect the pods from damage. Pod feeding can affect seed quality, yields, and can facilitate infection by fungal pathogens.  If the decision to spray is made, remember to check the PHI intervals of the product selected as most effective products will have 21-30 days PHI’s. Organophosphates, pyrethroids or pyrethroid+ neonicotinoid combinations will have good activity on BLB’s. If pods are mature and look yellow and dry, insecticides will be of no benefit and may actually delay harvest due to their PHI.  In addition to BLB’s, stink bugs and grasshoppers can also injure pods. Stink bugs will puncture or pierce through the pod and result in shriveled seeds, or seeds that do not develop. Grasshopper feeding on pods is very aggressive and they are able to remove chunks of pod tissue and seeds with their strong mandibles. A little stink bug feeding was noted in one of the fields scouted this week, though the level of damage and number of stink bugs was insignificant compared to that of BLB’s. Bean leaf beetles were by far the primary culprit of the damage observed in these fields. 

BLB adults are ¼” long with color variations from yellow, tan or red. Some will have two black spots on each wing cover, but others will have no spots at all. The one distinguishing characteristic of BLB adults is a black triangular mark at the top of their wing covers (Image 3). BLB’s have two summer generations and overwinter as adults. At this time of the year, the majority of the beetles we are seeing will be the ones of the second summer generation. These will be the beetles that will overwinter and come back out the following spring to feed on soybean seedlings. This is just a reminder that it is important to check fields all the way through harvest, to make sure that there aren’t any late season unexpected issues threatening our yields. For more information on insect damage to soybean pods or bean leaf beetle management, contact your local FS crop specialist. 

Image 1. Soybean field with bean leaf beetle (BLB) pod and leaf damage. Note yellow spot in the center, a BLB heavily damaged area.

Image 2. Plants with severe BLB defoliation and pod feeding.

Image 3. Color variation of BLB’s. Note the black triangular spot behind thorax.