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Section 26.6.9: Corn Earworm

Helicoverpa zea

Time of concern: Mid-July through September. Tassel until harvest.
Key characteristics: The yellowish, round eggs, laid mostly on silks, are deposited singly. Larval feeding is typically confined to the ear tip.  The adult moth has a wingspan greater than one inch and varies in color from yellowish tan to brown. Forewings have two dark spots. The larvae vary in color, with green, brown, or pink stripes and a tan head capsule. Skin is rough with characteristic short microspines that can be seen with magnification. Full-grown larvae are about 3/4 inch in length.

Management Option Guideline
Scouting/thresholds

CEW is a pest that annually immigrates from the south.
Processing sweet corn - Use a pheromone trapping system to detect the arrival and monitor the flight activities of the adult moths. Generally, the CEW is not a marketing concern for processing sweet corn. If it is a marketing concern, follow the protocols for fresh-market sweet corn below.

Fresh-market sweet corn - Use a pheromone trapping system to detect the arrival and monitor the flight activities of the adult moths. Trap numbers are also used to determine spray intervals. Green silk stage fields are most vulnerable to infestation by corn earworm. Application intervals can be adjusted based on trap counts. See Table 26.6.1 below.

Fresh Market Sweet Corn IPM Scouting Procedures

The most recent trap catches of the WNY Sweet Corn Pheromone Trap Network are posted and updated each Tuesday during the growing season.

Natural enemies

A variety of natural enemies help suppress CEW infestations including minute pirate bugs and parasitoids. Use Natural Enemies of Vegetable Insect Pests for identification of natural enemies.

Predators can reduce the number of CEW eggs. To maximize the effects of these biological agents, use insecticides that will conserve natural enemies. Bt varieties have been effective against CEW while conserving natural enemies.

Resistant varieties The only highly resistant varieties available are Bt sweet corn varieties.  Single Bt gene varieties have provided excellent control of European corn borer (ECB) and fair to good control of CEW and fall armyworm (FAW) under typical insect pressure.  Under moderate to high pressure, supplemental insecticide sprays for CEW and FAW may be warranted for single gene Bt sweet corn varieties.  Dual Bt gene sweet corn has provided excellent control of ECB, CEW and FAW.
Planting date If feasible, plant early and thereby harvest before the arrival of migrant CEW's to minimize the chance of damage.
Insecticide Resistance Management

The Insecticide Resistance Action Committee (IRAC) has classified insecticides into resistance management groups. Most insecticides include an IRAC group number on the front page of the label. Alternating between insecticides with different group numbers will help avoid the development of resistant insect populations.

Crop rotation,
Postharvest, and
Sanitation
These are not currently viable management options.
Pesticides Cornell Integrated Crop and Pest Management Guidelines for Commercial Vegetable Production

Table 26.6.1 Average CEW pheromone trap catches during silk stage

Per day Per 5 days Per week Days between sprays
<0.2 <1.0 <1.4 no spray (for CEW)
0.2-0.5 1.0-2.5 1.4-3.5 6 days
0.5-1.0 2.5-5.0 3.5-7.0 5 days
1.0-13.0 5.0-65.0 7.0-91.0 4 days
over 13 over 65.0 over 91.0 3 days
Spray intervals should be lengthened by a day if daily maximum temperatures were less than 80°F for the previous two to three days.

The most recent trap catches of the WNY Sweet Corn Pheromone Trap Network are posted and updated each Tuesday during the growing season.