How To Produce A Clean Sweet Corn Crop
December 8, 2011 
Some of the biggest challenges of producing a clean sweet corn crop are the caterpillars, says Rick Foster, an entomologist at Purdue University in Indiana. The list of caterpillars includes European corn borer (ECB), fall armyworm, western bean cutworm, and corn earworm.
European Corn Borer
ECB may be declining in importance, thanks to Bt field corn in the Midwest, but Foster says sweet corn growers in Michigan say they are seeing more damage from this pest than growers in Indiana, so it is still one to keep an eye on.
As black light traps can be expensive monitoring tools for this pest, Foster suggests walking through grassy areas around fields to determine pest presence. If 20 moths in 20 feet are kicked up, then it is time to take action. Foster also tells growers to look for whorl feeding. They will know it is time to spray if 20% of the plants show signs of feeding.
To manage ECB, Foster says sprays must take place before the pest gets to the ear. So the best time to spray is before the tassel emerges. Pyrethroids are the suggested control options.
Fall Armyworm
Providing more dramatic damage to the crop than other pests is the fall armyworm. Again, growers should look for whorl feeding damage in just a portion of the field.
Foster suggests using a pyrethroid insecticide at the late whorl stage to control armyworms.
Western Bean Cutworm
The western bean cutworm (WBC), however, is a relatively new pest to sweet corn growers in Indiana and Michigan, says Foster. It has been a pest of dry beans and corn in Nebraska for some time. In Indiana, the first damage was found in 2007. “For some reason, this pest has expanded its range and migrated east,” he says.
Foster suggests growers monitor insect traps for the pest. If WBC has migrated to the area, they will have problems with them in the future. According to Foster, growers need to be aware that the distribution of the pest often is clumped in certain areas of the field.
The key point is to treat for this pest before they move to the ears, similar to ECB and fall armyworm. The good news for growers is there are numerous foliar insecticides available to do the job.
Corn Earworm
Last but certainly not least is the corn earworm. A serious pest of sweet corn in the Midwest, Foster says growers really need to know the biology of the pest in order to gain control. The females lay eggs on green silks and when the larvae are ready, they will crawl to the ear tip and then find refuge in the ear. Once it is inside the ear, says Foster, the larvae are protected from insecticide sprays.
He tells growers if they are trapping more than 10 moths per night, they need to spray every two to five days until the silks turn brown.
“It is important to know what the corn earworm populations are so you can determine when to spray,” he explains. “You don’t know what the season will bring unless you have traps out.”
To kill corn earworm, growers must have the insecticide present on the silk when the eggs hatch, so it is a timing issue, says Foster. Control options, he says, again include the pyrethroids. With some concern about resistance developing, growers also have Coragen (DuPont Crop Protection) and Radiant (Dow AgroSciences) in their toolbox to use as well.
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