John Obermeyer and Christian Krupke
• European corn borer infestation only a concern in non-Bt corn.
• Some highly infested fields found too late.
• Before applying a control, determine if control is possible and/or economical.
First generation European corn borer appears to be causing only minor damage to non-Bt corn (Bt corn is still holding strong against this pest). However, calls this week from southern Indiana indicate that there are some highly infested fields. It is too late for control however, since the borers are burrowed into stalks and therefore are no longer accessible/treatable in this region.
Soon, borers will be entering corn stalks throughout the state. As noted above, once in the stalk or tassel, the borer is protected from insecticides and control efficiency drops dramatically, to the point that is scarcely worth attempting. Therefore, pest managers should closely examine stalks for borer entry before making control decisions. If treatment is necessary, it is recommended that the control material be applied before 1/3 of the borers have entered the stalk. Mid-vein leaf feeding indicates that stalk tunneling is soon to begin; frass accumulation in a leaf axil signals that the stalk has been entered by a borer. That borer has had the last laugh and will pupate in the stalk and emerge later in the year to reproduce.
Corn borer in stalk is impervious to insecticides
Source : purdue.edu