Corn Earworm
Figure 1. Corn earworm on sweetcorn (Photo by John Obermeyer).
https://extension.entm.purdue.edu/veg/cornearworm/
We are nearing the end of fresh silk on the dent corn population throughout much of the state. This means that for those of you who have late plantings of sweetcorn that have yet to silk, your threshold will drop back down to 1 moth per night on average to trigger an insecticide application. Keep a close eye on dent corn; if there is still green silk present, you can remain at the higher threshold (10 per night).
I have also had several calls voicing concerns that pyrethroid applications no longer work to control pests. This included a sweetcorn grower and tomato growers. While there are populations of corn earworm in the United States that are resistant to pyrethroids, I have not tested this in Indiana. It is possible that these products are losing efficacy against this pest as a result of resistance. However, it is also possible that the chemical is not holding up on the plant and therefore it’s not a matter of resistance but coverage and exposure. Sunlight and heat can both impact the breakdown and efficacy of pyrethroids. Given the hot and sunny weather we have been experiencing, this could be the cause of failure. Consider changing the time at which you apply the product or use a different mode of action (IRAC code other than 3) to improve the efficacy of your insecticide applications.