Corn earworm, Helicoverpa zea, is the primary economic pest of sweet corn in West Virginia. Infestation levels in the Northeast region of the United States vary with the year, time of season and farm location. Infestations of corn earworm in West Virginia result from migrant moths carried northward on storm fronts during mid-to-late summer. Sweet corn producers rely on timely pest monitoring and insecticide sprays to control this pest. However, insecticide control programs are costly, pose exposure risks to applicators, require considerable time and management, and can negatively impact non-target organisms and the environment.
Corn Earworm Control
Chemical Controls for Corn Earworm
When using insecticides for corn earworm control, it is important to time the first spray at early silking and then apply subsequent sprays on a schedule based on the flight activity of moths. Most corn earworm eggs are laid directly on the silks. Once larvae hatch, they quickly move down the silk channel and begin feeding on the ear tip, where they are protected from insecticide sprays. Therefore, it is necessary to target larvae before they enter the ear by treating silk tissue when moth pressure is high.
Pyrethroid insecticides (beta-cyfluthrin, bifenthrin, cyfluthrin, esfenvalerate, lambda-cyhalothrin, permethrin, zeta-cypermethrin) have been the traditional choice for control, but their control efficacy has declined in certain areas due to resistance in corn earworm populations.
Spray mixtures containing an alternative active ingredient plus a pyrethroid are often used to circumvent resistance development and improve control of other sweet corn pests. Rotations and mixtures with different active ingredients, such as chlorantraniliprole (Coragen), methomyl (Lannate), spinetoram (Radiant) and spinosad (Blackhawk), are increasingly used and can provide control. However, it is widely recognized that pyrethroids no longer provide enough ear protection making it necessary to switch to alternative products.
Biological Alternatives Resistant to Corn Earworm
Bt Sweet Corn Hybrids
The problems and challenges with foliar insecticide applications can essentially be eliminated with Bt sweet corn, which expresses insect toxic proteins from the bacterium, Bacillus thuringiensis (Bt), in plant tissue. This technology has revolutionized the way many corn insect pests are managed. There are three types of Bt sweet corn commercially available for lepidopteran pests: Attribute® hybrids (expressing Cry1Ab protein) and Attribute® II hybrids (expressing the Cry1Ab and Vip3A proteins) both from Syngenta Seeds, as well as Performance Series™ hybrids (expressing the Cry1A.105 and Cry2Ab2 proteins) from Seminis Seeds.
Attribute® hybrids have been commercially available since 1998, and acreage of this hybrid has increased significantly since its introduction. However, effectiveness of the Cry1Ab protein and the Attribute® hybrid has varied for controlling corn earworm, particularly in the southern United States. Recent field trials conducted in West Virginia have shown that Attribute® II hybrids can provide excellent control of corn earworm larvae. Growers using Attribute® II hybrids would likely not need to use supplemental insecticidal sprays, except for secondary pests.
Due to the yearly migration of potentially Cry1Ab-resistant moths from southern regions, the risk of further resistance development in the entire Northeast will likely increase and may compromise the reliability and durability of other Bt proteins.
Integrated pest management can further delay the evolution of resistance and must also be incorporated into future corn earworm management plans. Integrated pest management (IPM) practices, such as monitoring, crop rotation, rotation of Bt hybrids that produce different Bt proteins and judicious use of insecticides, are all highly compatible with the goals of IPM and insect resistance management for corn earworm.
Author: Daniel Frank, WVU Extension Entomology Specialist
Last Reviewed: April 2018
Recommendations for the use of agricultural chemicals are included as a convenience
to the reader. The use of brand names and any mention or listing of commercial
products or services does not imply endorsement by West Virginia
University Extension Service nor discrimination against similar products or
services not mentioned. Individuals who use agricultural chemicals are responsible
for ensuring that the intended use complies with current regulations and conforms
to the product label. Be sure to obtain current information about usage regulations
and examine a current product label before applying any chemical. For assistance,
contact your county Cooperative Extension agent.