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Practically everyone who has handled ears of corn either at the mature or immature stages has observed the corn ear worm. The larva varies in color from a light pink or rose to a dark brown and is about 2 inches long when fully mature. The moth is light-colored, varying from shades of greyish to brownish, and it has a wingspread of about 1 ½ inches. The insect passes the winter in the pupal stage and when the weather becomes warm the moths emerge, fly around, and lay their eggs on various parts of the host plant. Upon hatching, the larvae attack the silks of corn and later the kernels. When the larvae are fully grown, they leave the ear of corn and pupate in the soil. This insect also attacks a number of other plants, including tomatoes, beans, vetch, clovers, alfalfa, and the bolls of cotton. When this insect attacks tomatoes, it is called the tomato fruit worm and it is referred to as the cotton bollworm on cotton.
The ear worm can’t survive the winter in the northern states and hence the damage is not nearly as great there as in southern areas. Infestations in the northern states are a result of migrations of the insects from the south. One generation is produced in the northern states each year, 3 or 4 in most of the corn belt section, and as many as 6 generations in the southernmost areas.
How to Control Corn Ear Worm Insect?
The use of insecticides in ear worm control is primarily limited to sweetcorn and seed producing fields of dent corn. Applications of a oil-fortified DDT emulsion spray to the silks provides the most effective and practical control for plantings of commercial size. A mixture of three quarts of 25% emulsifiable DDT together with 2 ½ gallons low viscosity, white mineral oil in 25 gallons of water should be applied per acre. Two or three applications are necessary to provide effective control depending on the degree of infestation. The first application should be made when about 25% of the ears have started to silk and the other applications should be made at three-day intervals thereafter. Applications should be made with a ground sprayer using at least 150 pounds of pressure per square inch. Although airplane applications provide effective borer control, they are not recommended for use in ear worm control. Cattle which are being fattened for market should not be fed silage or fodder that has been treated with DDT.
Late fall plowing is effective in control corn ear worm insect because many of the pupae are brought to the surface where this insects are destroyed by the low temperatures that prevail at the time of year. There appears to be some variation in natural resistance to the insect among certain strains or varieties of corn. Damage is usually greatest with hybrids which have poor ear-tip coverage.
Delorit, Richard, et al. Crop production. Prentice-hall: New jersey