How to Control Corn Earworm in Sweet Corn

Corn earworm (Helicoverpa zea) is potentially the most destructive to sweet corn production. Because it bores directly on the market product, is difficult to control, and is common in high numbers at the end of the season, most insecticides used on sweet corn target this pest. Not only it damages on sweet corn, but also the corn earworm is a serious pest of cotton and tomatoes. Once earworm has become established within the ear, control is impossible. Earworms spend a relatively short period of their life feeding at the point of sweet corn that can receive an adequate insecticide application. An effective program, especially on late season corn, is necessary to ensure that damaged ears are kept to a minimum.

Earworms are variable in color, but they have a brown head without markings and numerous microscopic spines covering their body. Full grown larvae (1-1/2 inch long) are lightly striped and vary in color from a light green or pink to brown. Corn earworms are moderately hairy larvae that vary from yellow, to green, to red to brownish black. They may be found feeding in the ear tips following silking. The larvae are cannibalistic, rarely is their more than one per ear or whorl.

The moth has a wing span of 1 to 1-1/2 inches. The front wings of the male are usually a light yellowish olive; those of the female are yellowish brown to pinkish brown. Each forewing has a dark spot in the center. The dome-shaped-egg is usually white when first laid but develops a reddish-brown band before hatching.

An Integrated Pest Management plan that deals with the earworm at all five stages is the best way for corn growers to combat them.

Cultural Controls

There are a number of approaches that growers can implement to control corn earworm besides just spraying insecticides. This includes selecting the best varieties and planting dates. Varietal selection is very important. Corn hybrids having a long, tight fitting shuck appear to suffer less damage than those with loose shucks. The key factor determining the relative risk of corn earworm attack is planting date. Early and midseason we typically have fewer corn earworm moths to lay eggs on the silks. But late-planted corn will be late-silking corn, and many more moths are searching for egg-laying sites at this time. In addition, late in the season, the field corn crop is producing high numbers of corn earworm moths and is not attractive to the moths for egg laying.

Spray Coverage

Spray solution should be driven deep into the silks to be of maximum benefit. The center third of the plant is the only zone that needs to be protected. Ground application has always been shown to be superior to aerial application, particularly when using drop nozzles on each side of the row directed towards the ears. A spray pressure of 30 psi or higher is recommended.

Preventive Management

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 worm free ears during early and midseason. Control is more difficult late in the season. Even shortening spray intervals may produce only 90% clean ears.

An IPM Approach

Since moth intensity varies considerably during the season, it makes good sense to monitor adult activity and adjust the need for sprays accordingly. Pheromone traps need to be examined twice a week for corn earworms beginning in early June to determine moth activity and the need to spray. Special attention should be given to late planted fields and fields with green silks. Moths should be removed from traps, counted, destroyed, and removed from the field during each visit.

Spring moth arrival

  • Use pheromone traps to determine the main flight period for moths. Moths mostly fly under cover of night and go unspotted.
  • At first sign of moths, release trichogramma wasps to destroy eggs.

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