Source: Dominic Reisig, NCSU COOPERATIVE EXTENSION SERVICE, 8/11/17


I have received a number of calls and reports of very high earworm numbers in soybeans that are not blooming or at full bloom. Our online threshold calculator for earworms in podding beans can be found by visiting soybeans.ces.ncsu.edu, clicking on “insect management”, clicking on “thresholds” and scrolling down to the online corn earworm in soybean threshold calculator link. Should you treat soybeans blooming or prior to bloom?

Prior to bloom: Our official defoliation threshold is 30% defoliation throughout the canopy until bloom or two weeks prior to bloom (depending on how the crop looks) and 15% defoliation after bloom. A good guide to estimating defoliation can be found here.

These thresholds were recently re-evaluated in the Midsouth. Yield loss started somewhere after 66% defoliation at V6 in these studies. Incremental defoliation did not have an effect if soybeans were defoliated multiple times at 17.5% and 33% defoliation, but had a small effect if soybeans were defoliated multiple times at 66% defoliation.

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