Before we had Bt (Bacillus thuringiensis) to control European Corn Borer (ECB) in corn production, the pest had the potential to cause large yield losses. But European Corn Borer can be controlled effectively without Bt. In fact, growing conventional corn without ECB damage is not more difficult, or more expensive, for the operation, but it does require an understanding of the pest’s life cycle for best practices in management.
Life cycle of European Corn Borer
The ECB life cycle has four separate stages:
- Adult moth
The larval stage does the damage, and is where control measures are applied to crops. Depending on the region of corn production, there can be 1-4 generations of ECB per year, although two generations per year is most common.
First generation ECB larva overwinter inside corn stalks and corn cobs, which provide protection for the larva from weather and predators. In early spring, the larva become active and convert into the pupa stage. Moths then emerge in mid-May through mid-June.
ECB adults (moths) are nocturnal in activity. They mate, and the female moth lay eggs in clusters of 5-30 eggs on the underside of corn leaves near the midrib. Eggs hatch in 4-10 days, and the larva feed in the whorls of the plant, which causes a shot-holed appearance on the leaves as they continue to grow.
As the larva increase in size, they borer into the tender stalk, forming a cavity within the stalk. The larva then pupate and the second generation moth emerges 7-14 days later. Second generation ECB moths mate, and the female moth lay eggs on the underside of leaves. These lava hatch and feed on remaining pollen in leaf axils and also on corn silks. Eventually, the second generation larva feed and enter the shanks of ears, ear tips and upper half of corn stalks.
Damage to corn plants from ECB
- Stalk cavity damage by first generation larva feeding, which limits the normal flow of nutrients and water within the corn plant and reduces its yield potential.
- Stalk cavity damage by first and second generation larva causing harvest issues from weakened, broken and lodged stalks.
- Shank feeding which causes ear droppage, making the ear unharvestable and is a direct yield loss.
- Kernel loss from borer ear-tip feeding.
- Stalk damage also provides an entry point for secondary diseases and insects.
How to control ECB in conventional corn
Scouting fields for eggs and larva for both generations of ECB has been done effectively for years before Bt corn was introduced in 1996.
Local extension agencies typically report pest alerts, including ECB moth flights in your area, which help you to identify when egg and larva scouting should begin.
Scouting needs to be done on a weekly basis. Start by examining 10 plants for eggs and larva evidence in five random locations across each field. Generally speaking, when 20-30 percent of plants are infested with ECB, control through an insecticide application can be economical; though, this depends on the cost of the treatment you’ve chosen and the current price of corn.
Control with insecticides
Timing an insecticide with life cycle stage is important to get acceptable control of ECB. Once the larva have entered the stalk, shank or ear tip it is very difficult for any insecticide to make contact with the larva and offer acceptable control.
You can typically get effective control of first generation ECB larva in conventional corn with granular insecticides that continue to stay in the whorls where the small borer feed, rather than through liquid insecticides that will dry and grow out of the borers feeding area. This is also because first generation ECB larva occurs during the rapid growth stage, and small larva are much easier controlled than large larva.
With second generation ECB larva, you have several options for liquid forms of insecticide to help control the pest.
Taking the time to scout your fields regularly for above-ground insects is an important part of making a conventional corn crop successful. But it’s a major myth of growing conventional corn to assume that you won’t be successful because, "insect damage will decimate my conventional corn crop" — instead, there are a number of management approaches to controlling these pests, including European Corn Borer.
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