Indiana Prairie Farmer publishes a column written by Tom Bechman with the help of CCAs for CCAs and their clients. With permission from Prairie Farmer we are posting these Soybean and Corn Pest Beat articles on the CCA website. Many thanks to the authors and the support of Indiana Prairie Farmer.
Soybean Pest Beat Articles
Get ahead of bean leaf beetles by scouting
Answers are from the Indiana certified crop adviser panel: Gene Flaningam, Flaningam Ag Consulting, Vincennes; Carl Joern, Pioneer, Lafayette; and Greg Kneubuhler, G&K Concepts, Fort Wayne.
My soybeans are emerging and I’m seeing some bean leaf beetles. I’m thinking I should have used an insecticide. Should I have? Will I be paying for it at harvest?
Flaningam: Bean leaf beetles in emerging soybeans are a concern if the beetles are feeding on the stems, cotyledons and leaves. A heavy infestation can reduce plant stands and cause the plant to be susceptible to soilborne diseases and root diseases. Treated seed today includes insecticide for a broad range of issues. Bean leaf beetles can feed on pods during the reproductive stage of soybeans, causing grain quality issues and potentially yield loss.
Joern: Early-planted soybeans are often your farm’s highest-yielding fields, but this practice comes with added risk. The ability to plant soybeans earlier has been made possible through the adoption of seed treatments.
Fungicide seed treatments provide critical early protection, giving seedlings time to establish a strong root system and defend against damping-off pathogens. Insecticide seed treatments help mitigate early-season pest pressure, particularly from bean leaf beetles, which are drawn to the first-planted fields in an area. Skimping on seed treatments could lead to stand reductions severe enough to warrant replanting — potentially costing more at harvest than the initial investment in protection.
If pest pressure does arise, a rescue foliar insecticide application may be necessary if defoliation exceeds 30% of the plant. Careful scouting and timely decision-making can help protect your early soybean stands and maximize yield potential.
Kneubuhler: Bean leaf beetles are quite common every year and can be observed in the first soybeans to emerge. They feed on foliage early on and pods later in the season. Their feeding can transmit what’s called bean pod mottle virus, which can potentially reduce yields and even seed quality. It typically takes quite a bit of leaf feeding early in the season to create a yield issue.
Economic thresholds range from two to eight beetles per plant, which is a rather high number. To warrant spraying early in the season, look for significant defoliation and thresholds reaching those numbers. Generally, early in the season we don’t see a huge need for treatment. The best time to use insecticides is late in the season, as this pest will feed on pods, and that creates a larger economic hit. Pyrethroid insecticides are very effective on bean leaf beetles, and the cost is rather low.
