Southwestern Corn Borers Showing up Early in Non-Bt Corn

Yesterday (4/30), I had a call from a consultant who found about 20% infestation of 3-4 day old SWCB in Non-Bt, V6 stage corn in the Minter City area.  There were places in the field that averaged 40-50% infestation, but overall was about 20%.  It is not unusual for us to have to treat  1^st generation corn borers in MS in a few locations every year, however, it is very unusual to find them in that area of the state on April 30^th.  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 SWCB yet and almost no one has their 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 SWCB.  Feeding from SWCB 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.  SWCB 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 20-25% infestation.  If you have to treat first generation SWCB it is critical that you use a pyrethroid.  We have had decent luck controlling SWCB down in the whorl with pyrethroids.  If possible go 20 GPA by ground if you need to treat.

SWCB Larvae-Chris Daves