European Corn Borer (Ostrinia nubilalis) caterpillars begin by feeding on leaves, whorls and tassels before boring into stalks, ear shanks and ears. Once inside the plant, their tunnels weaken stalks and can cause tassels or stalks to break. Small holes accompanied by sawdust-like frass are a useful clue that a caterpillar has bored inside. The larvae can also tunnel directly into ears. European Corn Borer overwinters as mature larvae in corn stalks and other infested plant debris, allowing populations to carry from one season to the next.

How to Fix It
Inspect young corn: Look for feeding damage, frass and small holes while caterpillars are still feeding externally.
Remove caterpillars early: Hand-pick exposed caterpillars before they bore into stalks or ears, where they become difficult to reach.
Remove infested stalks: Cut down and dispose of badly infested plants and stalks after harvest.
Clean up after harvest: Don't leave infested corn stalks standing through winter; the larvae can overwinter inside them.
Encourage beneficial insects: Predators and parasitic insects help suppress eggs and young caterpillars.
Bt: Bacillus thuringiensis var. kurstaki can control young exposed caterpillars, but it will not reach larvae once they have bored deeply into the plant.
Crop rotation: Moving corn can help in a garden setting, although adults can fly into new plantings from surrounding areas.