Fall armyworm (April 26th, 2013)

People are planting field corn and garden corn across Texas this week and will undoubtedly face caterpillar damage to ears starting just after silking. The corn earworm, Helicoverpa zea, is the usual culprit found in the tips of corn ears. However, there is another species here that does far more than just tip damage. The fall armyworm, Spodoptera frugiperda, feeds in ear tips when young and then a large percentage of them bore into the side of the ear when they are older, approximately in the 4th instar. Fall armyworms are common and significant pests from the Texas Gulf Coast to well north of Lubbock, although usually less of a problem north of Amarillo. No one has yet published a scientific paper on the yield loss associated with fall armyworms in ears of corn, but we got a good handle on it with our 2012 research (which we are repeating this year). One fall armyworm causes an average of 0.24 pounds of yield loss when it gets in the lower 2/3 of an ear, and the grain that remains is often riddled with fungi. The fungi both reduce the weight of infected kernels and cause a significant increase in fumonisins; very dangerous toxins produced by certain fungi. Our research last year showed that if insecticides are to be used to protect ears they should be applied at silking. Unlike corn earworm, fall armyworm continues to lay eggs in corn until the time of harvest, so an additional insecticide application might be needed. Unfortunately, fall armyworms are significantly less susceptible to synthetic pyrethroid insecticides than are corn earworms, and control is often difficult to achieve with the insecticides available to gardeners in local stores. Farmers have access to newer, significantly more effective insecticides. Transgenic (Bt) corn can be effective on both corn earworm and fall armyworm, but different types of Bt corn have different abilities to control these pests. 

A fall armyworm larva in an ear of corn.

Typical fall armyworm damage to corn ears. The larvae consume many kernels and then the fungi move in and infect many more. 

Corn earworm larva in the tip of an ear of corn.