The corn earworm is the most serious sweet corn pest because it feeds directly on the marketable product. Once
earworms have become established within the ear, control is impossible, so a preventive program in necessary.
Earworms are variable in color, but they have a brown head without markings and numerous microscopic spines covering their body. Earworms spend a relatively short period of their life feeding in a site that can receive an adequate insecticide application. A preventive program, especially on late season corn, is necessary to ensure that damaged ears are at a minimum.
Corn earworms overwinter as pupae in underground cells. Some adults from these pupae begin to emerge as early as late March, others may not appear until August. There are generally four generations each year, however, overlap is great and adult moths that can lay eggs may be present in significant numbers throughout most of the growing season.
Female moths search out green silks on which to lay single eggs. Following hatch, the small larvae often eat the egg shell before beginning to feed on the silk. Corn earworms generally complete their development in 14 to 16
days. Full grown worms leave the ear and pupate in the soil. The new adult will be active in another 10 to 14 days.
A preventive program against corn earworms may begin when 10% of the ears are silked. Repeated sprays at three to five day intervals until 90% of the silks have wilted should give a high percentage of earworm-free ears during early and midseason. Control is more difficult late in the Season. Late in the season, even shortening of spray intervals may produce only 90% or fewer clean ears. Sprays should be driven deep into the silks. Corn hybrids having a long, tight-fitting shucks suffer less damage than those with shorter or looser shuck leaves.
Biological: The hemipterans, Orius, Nabis, Gencoris, and the lacewing, Chrysopa, are predators. Common wasp parasites include Brachymeria ovata, Microplitis croceipes and Trichogramma spp. The tachnids, Archytas
marmoratus and Winthemia quadripustulata are effective parasites. The fungus, Nomuraea rileyi, and the microsporidan, Nosema heliothidis, are also damaging to the earworms. Bt sweet corn hybrids (Attribute™) provide more than 95 % control of corn earworm damage to the ears.
However, it is necessary to continue to monitor Bt sweet corn for corn earworm activity and use supplemental insecticide sprays when necessary.
Cultural: The time of planting will have a marked effect on injury by this insect, but will not always be the same in different years; i.e., occasionally early-planted corn will be injured, but in most years the later plantings of
sweet corn are at greatest risk to corn earworm injury. The moths prefer to lay their eggs on fresh corn silks, so corn which silks before or after the greatest abundance of moths will largely escape infestation. Generally, sweet corn which silks after most of the field corn has begun to dry down will be exposed to the greatest corn earworm egg laying. Planting of resistant varieties of sweet corn will greatly reduce earworm damage. Corn hybrids that have tight husk leaves and that provide complete coverage of the ear have reduced ear damage by corn earworm.
Monitoring: Egg laying occurs only while silks are still green, but sprays need to be repeated at 2 to 7 days intervals while silks are fresh. Once silks dry, no additional corn earworm sprays are necessary. Time of planting,
intensity of moth flight and temperature will affect spray intervals. Pheromone traps are available for monitoring this pest to determine the need for insecticide sprays and their intervals.
Ambush 2 E (permethrin)- Apply as a foliar treatment at 6.4 to 12.8 fl oz per acre to a limit of 76.8 fl oz per acre per season.
Asana XL (esfanvalerate)- Apply as a foliar treatment at 5.8 to 9.6 fl oz per acre to a limit of 96 fl oz per acreper season.
Baythroid 2 (cyfluthrin)- Apply as a foliar treatment at 1.6 to 2.8 fl oz per acre to a limit of 10 applications per season.
Capture 2E (bifenthrin) - Apply as a foliar treatment at 2.1 to 6.4 fl oz per acre to a limit of 12.8 fl oz per acre per season. The long Restricted Entry Interval limits the use of this product to machine harvested field for
processing. Only a small fraction of the acreage in Kentucky is harvested by machine.
Diazinon AG 500 (diazinon)- Apply as a foliar treatment at 1 to 1-1/4 pt per acre.
Lannate 90 SP(methomyl)- Apply as a foliar treatment at 1/4 to ½ lb per acre per season to a limit of 8 lb per acre per season.
Pounce 3.2 EC (permethrin)- Apply as a foliar treatment at 4 to 8 fl oz per acre to a limit of 48 fl oz per acre per season.
Sevin 80 WSP (carbaryl)- Apply as a foliar treatment at 1-1/4 to 2-½ lb per acre to a limit of 8 applications per acre per season. Allow at least 7 days between sprays.
Warrior 1EC (lambda-cyhalothrin)- Apply as a foliar treatment at 2.56 to 3.84 fl oz per acre to a limit of 3.84 pts per acre.