Infestation of corn earworm can occur anytime from June to first frost. Feeding by larvae causes ragged injury to leaves in whorl stage corn, but damage during this period is usually limited to isolated plants. Infestation during the silking period results in damage to the tip of the ear.
Source of information
J.P. Michaund (http://entomology.k-state.edu/extension/insect-information/crop-pests/corn/cornearworm.html)
Pest photo source