Description of the Pest
Corn earworm moths are most active during evening and night. Adults are robust moths about 0.75 inches long with a wingspan of 1 to 1.5 inches. They can be olive green, tan, or dark reddish brown. Young caterpillar larvae are greenish with black heads and conspicuous black hairs on the body. Fully developed caterpillars are about 1.5 inches long and range from pale green or pinkish to brown.
The corn earworm may be present throughout the season but is most abundant during August and September. Larvae feed on leaves, buds, flowers, and pods, often damaging the beans.
Many natural enemies attack corn earworm eggs, including several species of Trichogramma. Most parasitized eggs turn black, but there may be a lag period before they do so. Generalist predators such as lacewings, minute pirate bugs, and damsel bugs feed on corn earworm eggs and small larvae. Plant habitat that attracts natural enemies and avoid the use of broad-spectrum pesticides known to harm natural enemies.
Organically Acceptable Methods
Use biological control, Bacillus thuringiensis, and the Entrust formulation of spinosad for an organically certified crop.
Monitoring and Treatment Decisions
Sampling should start at bloom in conjunction with sampling for lygus bugs. Inspect the sweep net for small caterpillars. While sweeping is not an effective sampling method for corn earworms, the presence of small caterpillars in the net indicates a problem may be developing. Beating and inspecting for caterpillars on pans, sleds, or sheets will provide some indication of the presence of small caterpillars. There is no precise economic threshold established for initiating control for corn earworm on beans.
Spray if the following conditions are all true:
- Small caterpillars appear in the sweep net.
- Small caterpillars can be found throughout the field.
- Young pods are present on plants.
|Common name||Amount per acre**||REI‡||PHI‡|
|(Example trade name)||(hours)||(days)|
|Not all registered pesticides are listed. The following are ranked with the pesticides having the greatest IPM value listed first—the most effective and least harmful to natural enemies, honey bees , and the environment are at the top of the table. When choosing a pesticide, consider information relating to air and water quality, resistance management, and the pesticide's properties and application timing. Always read the label of the product being used.|
|(Intrepid 2F)||10–16 fl oz||4||7|
|MODE-OF-ACTION GROUP NUMBER1: 18|
|COMMENTS: Suppression only.|
|(Coragen)||3.5–5.0 fl oz||4||1|
|MODE-OF-ACTION GROUP NUMBER1: 28|
|(Steward EC)||6.7–11.3 fl oz||12||7|
|MODE-OF-ACTION GROUP NUMBER1: 22A|
|D.||BACILLUS THURINGIENSIS ssp. KURSTAKI#|
|MODE-OF-ACTION GROUP NUMBER1: 11A|
|COMMENTS: Control is maximized by thorough coverage and by making applications when larvae are small.|
|MODE-OF-ACTION GROUP NUMBER1: 5|
|COMMENTS: Do not apply more than 12 oz/acre per season of Success or 3.75 oz/acre per season of Entrust. For blackeyes, apply with oil.|
|**||Mix with sufficient water to obtain full coverage.|
|‡||Restricted entry interval (REI) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without protective clothing. Preharvest interval (PHI) is the number of days from treatment to harvest. In some cases, the REI exceeds the PHI. The longer of two intervals is the minimum time that must elapse before harvest.|
|#||Acceptable for use on organically grown produce.|
|1||Rotate pesticides with a different mode-of-action group number, and do not use products with the same mode-of-action group number more than twice per season to help prevent the development of resistance. For example, the organophosphates have a group number of 1B; pesticides with a 1B group number should be alternated with pesticides that have a group number other than 1B. Mode-of-action group numbers are assigned by IRAC (Insecticide Resistance Action Committee).|