On April 30, I had a call from a consultant who found about 20 percent infestation of three- to four-day-old Southwestern corn borers in non-Bt, V6 stage corn in the Minter City, Miss., area. There were places in the field that averaged 40 to 50 percent infestation, but overall was about 20 percent.
It is not unusual for us to have to treat first-generation corn borers in Mississippi in a few locations every year, however, it is very unusual to find them in that area of the state on April 30. Looking back at old trap count records, we generally start catching moths in that area around May 17 to May 25. This is a full month ahead of schedule.
Most folks are not even thinking about scouting for Southwestern corn borers yet and almost no one has traps up yet.
First-generation corn borers are very easy to scout for. I would not spend my time looking for eggs. Look for feeding from the small larvae, then pull the whorl and verify that it is Southwestern corn borers. Feeding from Southwestern corn borers looks like small shot holes or window paning. CEW and armyworm feeding is much different and generally has much bigger holes eaten in the leaves.
Southwestern corn borers can be very damaging to small corn. It is not uncommon to get dead heart when the larvae tunnel down and hit the growing point on small corn, so scout closely.
Threshold is 20 to 25 percent infestation.
If you have to treat first-generation Southwestern corn borers, it is critical that you use a pyrethroid. We have had decent luck controlling Southwestern corn borers down in the whorl with pyrethroids.
If possible go 20 gpa by ground if you need to treat.