Mid-Season Insect Watch: European Corn Borer and Western Bean Cutworm

By the time you’ve reached the middle of the growing season, your corn crop is hopefully standing tall with ears that are developing kernels. 

But that also means now is the time to keep a keen eye out for the mid-season insect pressure that could get in the way of your yield potential. 

Let’s take a closer look at two pests—the European Corn Borer and Western Bean Cutworm—to be on the lookout for in order to protect your corn crop this growing season.

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European Corn Borer

The European Corn Borer (ECB) is a species of moth whose life cycle has four stages: egg, larva, pupa and adult moth.

When second-generation ECB moths mate, the female moth lays eggs in clusters of 5 to 30 on the underside of the ear zone leaves, usually near the midrib. These eggs are creamy white in color and resemble fish scales. 

Once they hatch, the larvae feed on remaining pollen in leaf axils and corn silks, eventually entering the shanks of ears, ear tips and upper half of corn stalks. 

How will ECB affect your corn crop?

ECB larvae can inflict harm to your crop in the following ways: 

  • Stalk Damage
    ECB-inflicted damage to the stalk can translate to harvest issues due to weakened, broken and lodged stalks. This also provides an entry point for additional insects and possible disease.
  • Shank Feeding
    When ECB larvae feed on the ear shank, it may cause ear droppage and make the ear unharvestable. This can result in significant yield loss at the end of the season.
  • Ear Tip Feeding
    Ear tip feeding by ECB larvae can lead to kernel loss, which will also impact your yield.

How do you scout for and control ECB? 

Most farmers in North America protect against the pest by planting Bt-corn, but you can still control ECB when growing conventional corn with effective scouting and timely insecticide applications.

ECB does its most damage in its larval stage, and that is where control measures should be applied. Once the larvae have entered the stalk, shank or ear tip, it is very difficult for any insecticide to achieve acceptable control. 

Local extension agencies usually report black light trap information regarding ECB moth flights in your area, which helps in knowing when egg and larva scouting should begin. 

Scouting needs to be done on a weekly basis, as small larvae are far easier to control. You’ll want to examine 20 to 25 plants in five random locations across each field to look for the presence of eggs and larval evidence. 

Generally speaking, when 25 to 30 percent of plants are infested with ECB, control is going to be economical; this depends, however, on the cost of treatment and the current price of corn. 

Treatment Options and Application Rates: 

Western Bean Cutworm

Western Bean Cutworm (WBC) is another pest that is capable of causing significant yield losses in corn production. 

WBC moths emerge from the soil in early July and begin to lay eggs a week before tassel emergence. This can continue for 3 to 4 weeks, through the milk stage of your corn. Eggs are laid in clusters from 5 to 50 on the surface leaves in the top half of plants. 

How will WBC affect your corn crop?

WBC eggs hatch within 5 to 10 days, and the small larvae begin to feed on pollen in the tassel. 

After all the pollen has been shed, larvae move to the ears, feeding on the silks and developing kernels. Unlike the cannibalistic corn earworm, multiple WBC larvae can exist on each ear. And each larva can feed on and destroy up to 12-20 kernels. 

This damage also allows secondary insects and disease to enter the ear, lowering the grain quality. 

How do you scout for and control WBC? 

Once the WBC larvae enter the ear, they are protected from insecticides. But with diligent weekly scouting and properly timed insecticide applications, WBC control is possible. Treatment is suggested when 4 to 8 percent of corn plants exhibit infestation. 

Treatment Options and Application Rates: 

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