Pay attention to bean leaf beetles

By Tom J. Bechman
The panel of Indiana Certified Crop Advisers provide advice on scouting in soybeans. If you’re thinking that it’s no longer necessary to scout soybeans for insects now, you might want to reconsider.
Question: When should I worry about bean leaf beetles at this point in the season? Is there any need to scout and spray for them, or will they just do cosmetic damage?
Jesse Grogan, LG Seeds, agronomist, Lafayette: Bean leaf beetles cause more than cosmetic damage. They can cause economic damage to plants and pods. They’re also virus vectors for bean pod mottle virus. It’s been on the increase. Scout now for injury to leaves on top of the plant and on young pods, where most damage occurs. Estimate percent leaf feeding and damage to young pods in several areas of the field. If there is 15% defoliation in the R1 to R5 growth stage or 5% damage in young pods with 10 beetles per foot of row consider using an insecticide.
Control of bean pod mottle virus is more complicated. Late-season insecticide applications do little to prevent development of the disease. Virus-laden bean leaf beetles must be killed early in the season when overwintering beetles invade fields. Earliest planted fields are at most risk. Using insecticide-treated seed at planting reduces risk. Fields with high amounts of early generation feeding can be treated with an insecticide later in the summer at a lower threshold level to reduce bean pod mottle virus damage.
Andy Like, co-owner, Daylight Farm Supply, Evansville: Scout for bean leaf beetles when you scout for other insects. The likelihood of sustaining significant economic damage from bean leaf beetles during the reproductive stage is rare. If more than 5% of pods are damaged, treatment may be warranted.
A more likely scenario would be that bean leaf beetles and other insect pests combined feeding is enough to justify an insecticide application. The bean leaf beetle also vectors bean pod mottle virus. However, the disease is most damaging when soybeans are infested with the virus early in the season rather than later.
Traci Bultemeier, DuPont Pioneer, accounts manager, Ft. Wayne: Most often in August and September bean leaf beetle feeding is cosmetic, though pod feeding can occur. In some instances it can be detrimental to yield. When pod feeding exists on 10% or more of the pods and 10 or more beetles are present per foot of row, the field has reached the economic threshold for treatment. It’s important to note leaf feeding as well, where 15% defoliation in the R1 to R5 reproductive stages and 25% or more defoliation from full seed to harvest is the threshold. If you consider applying an insecticide, note the harvest interval to be certain label restrictions are being followed.
Key points
Continue scouting for bean leaf beetles until harvest
Percent defoliation of the entire plant could trigger treatment
Become more familiar with bean pod mottle virus, vectored by bean leaf beetles
Pix a
Beetle at work- Bean leaf beetles can be orange like this one, tan or yellow, with or without spots. Look for the distinct black triangle behind the head.