Management of this pest in corn often lies with planting resistant hybrids and altering planting dates to avoid high densities of corn earworms. Resistant hybrids limit the amount of injury to both the leaf and the ear.
A combination of silks that are antibiotic to larvae and husks that are tight around the ear to alter larval behavior offer the most effective type of resistance.
Because of the tightness of the husk around the ear, feeding is limited to the ear tip, resulting in small larvae or larvae that leave the ear before completing development. Some Bt hybrids suppress corn earworm populations and reduce the amount of injury to the ear.
Neither crop rotation nor tillage significantly influences corn earworm survival. However, early-planted crops are most likely to escape peak populations of egg laying moths.
In addition, because egglaying moths prefer corn to beans, tomatoes, and other crops, borders or strips of corn planted as a trap crop around or within fields of other vegetables may reduce earworm densities on these less preferred crops.
This approach is likely to provide some benefit only if the corn is silking at the same time as the beans, tomatoes, or other crops are setting pods or fruit. Chemical control of the corn earworm can be expensive; most spraying occurs in sweet corn fields where a majority of the market value is in the quality of the ears.
Since larvae move down the silk channels as soon as they hatch, the timing of insecticide applications is very important. As the larvae move down the silks and under the husk of the ear, insecticide sprays become ineffective. For insecticides to work effectively, spray residues need to be present on the silks where the eggs hatch.
There will be no insecticide residue on new silk growth. Many producers follow a regular spray schedule based on the number of captured moths from pheromone traps. Others base the spray schedule on the injury sustained to the whorl or tassel. To the right is a spray schedule for corn earworm in sweet corn (from the University of Minnesota) based on the number of corn earworm moths caught in a pheromone baited cone trap.
(Counts are from a nylon trap; a full size Hartstack wire trap catches more moths, so multiply counts in the first column by 1.5 to get the approximate for a wire trap.) Bacterial insecticides containing Bacillus thuringiensis kurstaki (BT) represent a biological control approach. BT-based insecticides kill corn earworm larvae if the larvae ingest spray residues.
Because BT residues break down quickly and because earworm larvae do little or no feeding before entering an ear of corn, BT sprays have not been effective for corn earworm control in sweet corn or seed corn.
Rapid breakdown of BT (and the need for insects to ingest it) also renders it virtually ineffective for earworm control in snap beans. In tomatoes, however, BT can provide significant control of corn earworms if applications are well-timed and frequent.
Several natural enemies offer some control of the corn earworm. Predators such as the big-eyed bug (Geocoris sp.), the minute pirate bug (Orius sp.), and the spotted lady beetle (Coleornegilla maculata) consume corn earworm eggs and small larvae. Parasitoids such as Trichogramma species also attack earworm eggs.
Information Sourced From:
