By Dominic Reisig
Reports have come in on spray failures in some limited spots of pyrethroids over soybeans and cotton for bollworm/earworm. In addition, moths in both Georgia and Virginia have tested more resistant to pyrethroids than normal, which could mean that we have more in the system than usual, combined with a heavy bollworm/earworm year. There is no need to be alarmed, because we have good tools in our toolbox to take care of this, but you should be informed before you spend money on control.
Last week, my insecticide spray considerations for worms in cotton, sorghum and soybean were lacking this information. It’s difficult to say what might be going on in your specific area, since pyrethroids seem to work well in some spots, but not others. I would like to frame this in terms of risk. How much are you willing to take on? If pyrethroids have worked well for you in the past, you might want to take on some risk and try this as a spray. It is a risk, because, in soybeans, you could be spraying tobacco budworm (resistant to pyrethroids), or resistant corn earworm, and you will knock out beneficial insects in the system that will hold back things like loopers later in the season. The same holds true for cotton, although Bt cotton controls tobacco budworm- so no concern with than pest. If you are less risk averse, you could spray one of the more worm-specific products detailed in the article here.
If you have already sprayed a pyrethroid and have had a failure, you must come back with a worm specific product. Note that bifenthrin is a pyrethroid, and products like DoubleTake and Endigo also contain pyrethroids, but not bollworm/earworm-specific products.
Source:ncsu.edu