The corn earworm prefers the fruiting stage of the host but will also attack the foliage. Larvae feed on the silk hairs and then bore themselves into the ear, where they start to eat up the kernels. They can be seen feeding around or down the ear creating a track of damaged kernels and leaving a long line of brown frass. They are cannibalistic so usually per cob there is just one of them present. Numerous ragged holes appear at the tip of the cob and on developing leaf blades. Because they feed on floral structures and kernels and interfere with pollination and grain filling, the yield can be severely compromised. The damage creates an ideal environment for infection with other diseases.
Corn earworms overwinter as pupae in the soil, at depth of 5 to 10 cm. Robust adult moths start to emerge at the beginning of spring and are mostly active during the evening and night, more so with increasing temperatures. They have light-brown forewings, sometimes with olive shading. A wavy dark-brown band runs a few milliliters from the margins. Hindwings are white-gray and have a broad black band with a yellowish mark at the edge. Females lay white dome-shape eggs singly on fresh silk or foliage. The larvae vary in color (from pale green to reddish or brown), moderately hairy and about 3.7 mm long. They have tan or orange heads and a body covered with small black spots that correspond to microscopic spines. As they mature, two yellowish stripes develop on their flanks.
Parasitoid Trichogramma and Telenomus wasps can help to control the population to a certain degree by infesting the eggs of Helicoverpa zea. Larval parasitoids also exist. Other beneficial insects, such as green lacewings, big-eyed bug or damsel bugs are predators of eggs and small larvae. Some beneficial nematodes also work when injected at the tip of the ear. The fungal pathogen Nomuraea rileyi and the nuclear polyhedrosis virus also reduce populations of Helicoverpa zea. Application of bio-insecticides containing Bacillus Thuringiensis or spinosad work fine if they are applied in a timely manner. Mineral oil applied to the silk of each ear can also prevent corn earworm invasions.
Use an integrated approach with preventive measures together with biological control whenever available. In the field, pesticide use is rarely recommended because the larvae hide inside the cobs and are not exposed to the treatment. Insecticides containing pyrethroid, spinetoram, methomyl, esfenvalerate, permethrin or chlorpyrifos are effective against corn earworm when applied in a timely manner.
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