Based on moth trap catches, the second generation flight of southwestern corn borers (SWCB) is already beginning at some locations.  This second generation will pose a threat to non-Bt corn and an even greater threat to any relatively late planted corn.  This threat will be mostly isolated to places where there was a substantial first generation moth flight. 

Is it time to spray? 

1. First, I think it is 7-10 days too early to spray for SWCB.  Significant larval infestations will not typically develop until at least 7-10 days after moth trap catches show the onset of the second generation.

   

2. Second, many areas did not have much of a first generation.  I’m confident there will be problems with SWCB in parts of Henry, Weakley and Dyer Counties, but I can only guess about your farm unless you’ve been scouting or using moth traps.  Be prepared to spray in the near future if you had a substantial first-generation infestation.  I’ve demonstrated yield increases on non-Bt corn from 0 – 40 bushels per acre by making one insecticide application.  This response depends on SWCB infestation levels and the maturity of the corn.  Because scouting for corn borers is difficult, I can’t stress enough the value to running pheromone traps for this pest (and starting with the first generation).  Put that in your memory bank for next year.
3. Did you already spray an insecticide with your fungicide?  Oops, you probably wasted that one.  A pyrethoid insecticide should not be expected to provide more than 7-10 days of any residual control (less if it rains).  This is one reason UT recommends products such as Intrepid, Belt SC, Prevathon or Besiege when battling SWCB during the second generation.  These products provide longer residual control and are less affected by rainfall or irrigation.  Even then, spraying well in advance of the second generation will greatly reduce efficacy.