The presence of egg masses on the underside of leaves and young larvae feeding on the whorl leaves, tassels, and silks are the best indications of infestation. Ninety percent of the egg masses laid on sweet corn leaves are found on the lower surface of the four leaves above the primary ear, the lower surface of the primary ear leaf, and the lower surface of one leaf below the primary ear (Table 14). A blacklight trap is useful for determining the presence of significant numbers of potential egg-laying European corn borer females as well as other insect pests in the vicinity of sweet corn. Although pheromone traps also have been used (e.g., in Massachusetts), in general, they have not been as reliable as light traps or direct sampling. However, recent research has greatly improved pheromone trapping of this insect, which may serve as a better means of indicating population levels. Sampling in grasses along field edges and waterways for adults also may prove beneficial for determining when moths are present or otherwise in assessing populations.
Table 14. Location of 1,215 European corn borer egg masses on leaf blades of tassel-stage Silver Queen sweet corn in Delaware (Semeada and Mason).
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Leaf number Leaf surface Number of egg masses Percent of total
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8 lower 3 0.2
9 lower 37 3.0
upper 0 0.0
10 lower 165 13.6
(primary ear) upper 3 0.2
11 lower 325 26.7
upper 31 0.2
12 lower 378 31.1
upper 44 3.6
13 lower 152 12.5
upper 15 1.2
14 lower 31 2.6
upper 0 0.0
15 lower 31 2.6
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