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Scout for Bean Leaf Beetles
December 31, 1969
By Gabe Hardman, CCA Agronomist
First planted soybean fields, or soybean fields isolated from other soybean fields, generally attract bean leaf beetle and need to be monitored closely for early feeding of cotyledons and emerging unifoliates and trifoliates.
Don’t overlook this early season insect pressure in soybean fields; too much defoliation from bean leaf beetles can lead to yield loss in the fall.
Bean leaf beetle have two generations a year with three different periods of activity. Adult bean leaf beetle over winter in soybean trash and become active again in April and May when mating and egg laying occurs. Their offspring emerge as the first generation bean leaf beetle in June and July.
The first generation mate and the second generation emerge in August and over winter as adults. Second generation bean leaf beetles can directly affect soybean yields by feeding on pods and the beans, themselves.
When defoliation of cotyledons and unifoliate leaves reach 20-25% leaf loss, yield may become affected. As the trifoliates emerge soybeans may tolerate more leaf loss.
Soybean fields with moderate weed pressure and moderate bean leaf beetle numbers may be treated with herbicide and insecticide in the same pass. Fields with little or no weed pressure and moderate to heavy bean leaf beetle numbers should be treated with insecticide for the bean leaf beetle ahead of weed control.
Allowing the bean leaf beetle to feed past thresh holds to save a trip across the field may cost more at harvest time than treating for the beetles in the first place.
Controlling early bean leaf beetles on first emerging soybean fields will lower the first and second generation populations and hopefully save soybeans from heavy, late season pod feeding.
As soybeans begin emerging keep an eye on early bean leaf beetle feeding, especially on first emerging soybean fields in the vicinity.