Dated 6/93
Placed on the Web 4/95 by the Department of Entomology, NCSU
The corn earworm is the most serious of sweet corn in North Carolina. Other host plants are tomatoes, beans, cabbage, tobacco, field corn, sweet potatoes, cotton and soybeans. Night flying moths are grayish-brown, marked with darker areas near the tip of each of the forewings which have an expanse of 1/2 inches. The hindwings are lighter in color with dark areas near the margins. Fresh corn silk is the preferred egg-laying location. However, moths will deposit eggs near buds and growing tips of young corn. These yellowish eggs are laid singly with each female producing some 3000 eggs which hatch in 2 to 4 days depending on temperature. After feeding on corn silk a short time, caterpillars (larvae) move to the end of the ear and feed on the maturing kernels. Since caterpillars are cannibalistic, by the time they have entered the shuck and reached the kernels, only one of two "worms" survives. When fully grown, the caterpillars are about 2 inches long, brown to tan or even green in color and have light and dark longitudinal stripes. The head is always yellowish and the underside of the body lighter than the back. Larvae drop to the ground and burrow into the soil 2 to 8 inches to pupate. These insects overwinter as pupae. In mild winters, some may survive as far north as North Carolina. Most years, however, they are killed and a new crop of moths fly in from the South.
There appears to be three generations per year. The August generation, however, is the most severe and most difficult to control. Black light insect traps and sex pheromone traps can be used to monitor flight periods. Early silking is most attractive for moth egg laying and is the time for a tight spray program.
Although young corn may be severely damaged by corn earworms, we are concerned only with the protection of the ears from time of silking to time of harvest in this insect note.
In general, when corn is harvested in the Coastal Plain from July 10 to July 20, the infestation in the ears is relatively low, even if only a fair job of chemical control is carried out.
For best results spray when tassel shoots appear, 3 days later, then daily for 5 applications. Then apply at 2-3 day intervals until harvest. Corn tasseling from mid-July on will require daily sprays to ensure worm-free ears.
Methomyl (Lannate) 90% soluble powder 0.5 pound or methomyl (1.8 pounds/gal) 1 to 2 pints in 25 gallons of water/acre may also be used. Methomyl is used on the same schedule as carbaryl. Do not feed or graze methomyl-treated plants for at least three days after application. Methomyl is extremely toxic; therefore, follow label directions at all times but especially while measuring and mixing the concentrates.
Thiodicarb (Larvin) 3.2EC at 20 to 30 ounces/acre may also be used. The rate increases as insect populations increase. Do not exceed 10 applications per season.
Carbaryl, methomyl and thiodicarb have a 0 waiting period until harvest. Spintor 2SC at 6oz with a 1 day TLH is also effective.
Synthetic pyrethroids are effective against corn earworms. Either esfenvalerate (Asana XL) 0.68EC or permethrin (Ambush) 2.0EC or (Pounce 3.2EC) may be used. Ambush and Pounce also is available as a 25WP. Esfenvalerate and permethrin have a 1 day waiting period until harvest. Capture 2EC at 6.4oz with a 1 day TLH, Baythroid 2EC at 2.8oz with a 0 day TLH, Mustang MAX 0.08EC at 4oz with a 3 day TLH and Warrior 1EC at 3.8oz with a 1 day TLH may be used.
Commercial sprays should be applied at pressures of 100 to 150 pounds per square inch and directed toward the ear zone. Use two nozzles on each side of the row. When using wettable powders, it is advisable to have a 50 to 70 mesh screen in the spray line to prevent clogging of nozzles. Air blast sprayers are effective but require drive rows, 20 galls of water/acre, little or no wind and slow tractor speed.
Click here for suggested boom and nozzle arrangement for the satisfactory control of corn earworms in sweet corn.
Resistant Varieties - Where satisfactory, resistant varieties are available, they should be considered. The combination of a resistant variety such as Golden Security and a good spray program should result in a greater yield of "worm free" corn.
Carbaryl (Sevin) is recommended for use in the home garden. Apply carbaryl 50% wettable powder 4 tablespoonfuls or carbaryl 80% wettable powder 2 1/2 tablespoons per gallon of water. Thoroughly wet the silks of all ears until harvest is completed.
Dusts containing Sevin may also be used. They can be applied to the silks of each ear with a paint brush or hand duster.
The use of brand names and any mention or listing of commercial products or services in this publication does not imply endorsements by the North Carolina Cooperative Extension Service nor discrimination against similar products or services not mentioned. All pesticide recommendations provided in this publication apply to pest control in North Carolina. Individuals who use chemicals are responsible for ensuring that the intended use complies with current regulations and conforms to the product label. Be sure to obtain information about product usage in your locale and examine a current product label before applying any chemical. The information presented on pest biology is based on conditions in North Carolina and may not be applicable to your locale. For further information, we recommend that you contact the Cooperative Extension Service office in your county.
