Figure 8. European corn borer egg mass with numerous eggs on underside of corn leaf (M. E. Rice).

Techniques for detecting moths in field corn and sweet corn with blacklight and pheromone traps can be applied to seed corn. Once moth activity is detected, sampling should begin. Because of the low infestation levels required for making a treatment decision, carefully scout seed corn to obtain as accurate a sample of potentially damaging European corn borer as possible. Egg mass presence on the underside of leaves (Figure 8) and young larvae present anywhere on the plant are the best indicators of a potentially damaging population. In whorl-stage seed corn, check the whorl for evidence of leaf feeding. Twenty plants in each of five locations per field should be sampled to determine the percentage of plants that are infested. In corn that is in or beyond the pollination stage, the presence of egg masses on the underside of leaves, especially the three leaves located above the ear, the one at the ear node, and the three below the ear, is the primary means of assessing a potentially damaging European corn borer population. However, evidence of young larvae feeding on the leaf surface, in leaf axils, and around the leaf collar area also can be of value. Once the larvae bore into the leaf collar or other parts of the plant, control is generally not effective. Therefore, it is very important to detect egg masses and young larvae early in the infestation period.