An eastbound express, wreaking havoc on ears of corn about this time of year, may be one of your primary crop scouting targets if you are a Cornbelt farmer. Indiana farmers were warned for the first time last week. Illinois farmers heard about it for the first time two years ago, and populations are at record levels to the west in Nebraska and Iowa. This corn pest is called the Western Bean Cutworm, but the apparent misnomer is not something you should worry about. Worry about the worm on your corn.

Purdue entomologist Christian Krupke sounded the alarm on Friday after western bean cutworms had been captured in moth traps set across Indiana. For Indiana farmers, the populations apparently are light enough that Krupke says crop damage is not anticipated for the 2006 crop. "Last year the pest was found in Illinois. We started trapping the moths in Indiana this year, as well as Wisconsin, Michigan and Ohio. We found moths in all of those states. The highest concentrations of western bean cutworm moths we've found in Indiana are in northwest part of the state, closest to the sites of infestation in Illinois. We've also found moths in eastern counties, such as Randolph and Whitley. It is important to note, however, that the moth numbers are not very high and we haven't documented any damage by the pest yet in Indiana."

Not so for farmers and cornfields west of Indiana. In May of 2005, University of Illinois Extension entomologist Kevin Steffey wrote, “Until very recently, corn growers in Illinois have not had to be concerned about western bean cutworm, a cutworm species that attacks corn ears in midsummer. However, the distribution of western bean cutworms in Iowa has moved rather steadily eastward since 2000, encroaching on Illinois' western border in 2004.” The U of IL Integrated Pest Management guide says damage can sometimes be significant, “During years with severe infestations, multiple larvae per ear may be common. Under severe feeding pressure, 50 to 60% of an ear's kernels may be damaged.”

Populations spike periodically, say Nebraska entomologists, who have been studying the pest for the longest time, “Populations vary from year to year, but there is a tendency for higher numbers every six to eight years. Moth emergence tends to be greater in fields with sandy soils and may be increased by rainfall or irrigation.” The western bean cutworm got its name from its destruction of dry beans in Nebraska, but it will also be found on field corn, sweetcorn, popcorn, tomatoes and the fruit of nightshade.

For many farmers, western bean cutworm control this year may be too late, according to the Nebraska factsheet: “If eight percent of field corn plants have egg masses and/or small larvae, consider an insecticide application. This threshold or infestation level may need to be adjusted based on the crop’s value and control costs. If an insecticide application is required, timing is critical. If the eggs have hatched, insecticide applications should be made after 95 percent of the plant tassels have emerged, but before the larvae have a chance to enter the silks. Once larvae move to the silks, insecticide control is more difficult. If the eggs have not hatched and plants have tasseled, the application should be timed when most of the eggs are expected to hatch. Purple eggs should hatch within about 24 hours.”

However, if your scouting indicates significant problems with western bean cutworms, the Nebraska guide offers some help: “There is some evidence that synthetic pyrethroid insecticides will force larvae out of protective areas due to the irritation properties of the active ingredient. These insecticides may be more effective should the larvae reach the silks prior to treatment. Products that contain Bacillus thuringiensis as the active ingredient do not control western bean cutworms. Larval survival is also relatively high on currently available transgenic corn plants that express the toxin produced by B. thuringiensis (Bt corn). Bt corn hybrids containing the Cry1F toxin (Herculex I) are labeled for control of western bean cutworm larvae.” Yieldgard Bt hybrids will not control western bean cutworms.

Purdue’s Krupke says western bean cutworms create more hotspots instead of complete devastation, "In the worst-case scenarios, you may see a four-bushel-per-acre yield loss, which is significant. But even in places like Iowa where the pest is more prevalent, the western bean cutworm isn't a key pest -- it's more of a hotspot sort of insect, with some damage in some fields. You don't tend to see a 50-acre field entirely wiped out by this pest."

Summary:
Western bean cutworms, which originated in dry bean territory, have rapidly advanced eastward from Nebraska to attack cornfields as far east as Indiana and Michigan. Related to the corn earworm, they will create hotspots in fields with damage to kernels, as much as four bushels per acre. Farmers will lighter soils are more susceptible, and scouting will help with either rescue treatments or preparation for 2007.