Larvae that are feeding in the whorl, but haven't tunneled into the plant, can be killed with an insecticide. The smaller the corn, the more likely it can be killed by stalk borers. Stalk borers don't move very far from grass, so only the first four rows of corn next to grass would need to be sprayed. Stalk borer economic thresholds. If the number of infested plants exceeds the percentage given for the plant stage and market value selected, then an insecticide application can be economically justified.
Young plants have a lower threshold because they are more easily killed than older plants.
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