This season I’ve noticed a lot of soybean fields showing extensive bean leaf beetle feeding (see photos). Growers often discount the threat these beetles have against yield, but during early growth stages their feeding can be quite damaging.
Photos courtesy of Eric Ifft, Bayer CropScience, taken in Livingston County on Friday, May 26, 2017.
Where to start scouting: All the fields I looked at with extensive bean leaf beetle feeding were treated with fungicide seed treatment only. While there was a small amount of feeding in fields where insecticide seed treatment was used, it wasn’t close to an economic threshold. If you did not have your seed treated with an insecticide seed treatment, I would highly encourage you to scout those fields for bean leaf beetle feeding. The economic threshold is 40 percent defoliation, but I would contend that with our beans having “wet feet” and with recurrent cool, cloudy conditions it would “Pay to Spray” even at lower levels of defoliation. Stress-on-stress is never a good thing, and bean leaf beetles are one stress we can eliminate.
Potential issues: Bean leaf beetles can have three generations in a growing season, so they keep coming back. The adult beetles, shown in the photos above, may have already laid eggs in these soybeans fields. This means that we could have another outbreak of bean leaf beetles later in the season. Also, bean leaf beetles can vector a disease called bean pod mottle virus (BPMV) which can cause significant yield loss. There are no products that can be applied to soybeans to control BPMV since it is a viral disease, however growers can utilize foliar fungicides and insecticide treatments to remove other stressors, allowing the soybean plant to fight off the virus. This is similar to how the common cold is treated in humans. Doctors recommend rest and fluids, which do not treat the cold but allow our bodies to fight off the cold virus more effectively.
Treatment Recommendation: There are a lot of insecticides on the market that will provide knockdown control of bean leaf beetles. But I typically recommend my growers apply 2.8 oz. of Leverage® 360, a Bayer CropScience product. When buying an insecticide look for both knockout control of the current infesting population as well as additional weeks of residual control in case more beetles move into your fields.