Experts at Purdue University recommend scouting corn fields and traps for Western bean cutworm, saying a large percentage of this year’s eggs will be laid over the next two weeks. Christian Krupke, entomology professor, and John Obermeyer, integrated pest management specialist, say that although the relationship between trap catches and damage is not particularly strong (i.e., high trap counts does not mean high damage), traps are a good timing mechanism and presence/absence indicator. When they spike suddenly, it’s time to scout.
Scouting for Western bean cutworm is straightforward - a matter of walking fields and looking for egg masses, generally laid on the top surface of the plant’s upper, most upright leaves. Concentrate efforts on pre-tassel corn; that growth stage is preferred by female moths as the young larvae initially feed on pollen.
If 5% or more of plants surveyed have egg masses, treatment is advised. If needed, early insecticide applications are better than late ones – pyrethroid insecticides will offer enough residual activity in most cases for a few days of killing the tiny newly hatched larvae as they travel on their way into the plant’s whorl or leaf axils. They are very easily killed at that early stage, but once they get inside the whorl/ear of the plant they cannot be contacted with insecticides, so get them early.
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