Corn earworm picking up in soybeans and there are a lot of questions. How big will this flight be? Will tobacco budworm show up in concert with earworm? Are the earworm moths resistant to pyrethroids? At this point, the first two questions are impossible to answer. We do have some inklings about an answer to the third question, however, based on adult vial assay tests from both Suffolk, VA and Plymouth, NC.
Dr. Ames Herbert’s data from Suffolk, VA indicates that resistance could be high in some locations. Based on vial assay data, he is confirming survivorship in the 50% range. We would start considering a population tolerant/resistant at anything over 30% point- 50% survivorship is about as high as we have ever seen it. My student, Rachel Suits, has a much smaller data set (26 moths) from Plymouth, NC that only indicates 18% survivorship. This tells me that there are geographical pockets where resistance is not as prevalent. Beet armyworm numbers are increasing in areas of North Carolina and Virginia. These caterpillars are tolerant to pyrethroids. Soybean loopers have not migrated here in great number, but can be flared by the use of pyrethroids.
I encourage you to be risk averse and to make an investment that will pay dividends for your valuable crop. Consider applying Belt, Steward, or Blackhawk (the new name for Tracer) for corn earworm. If you have stink bugs and are in the R4-R6 stages, you might want to tank mix one of these products with a pyrethroid. A tank mix of a pyrethroid and acephate are an option, but will wipe out all beneficials. If you do apply a pyrethroid for corn earworm, do not follow this spray with another pyrethroid for worms.