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Armyworm numbers 'huge' in the Corn Belt

Agriculture.com Staff 06/22/2007 @ 9:05am

Armyworm moths in "huge" numbers are being captured in Illinois and Iowa, according to a University of Illinois (U of I) report.

Extension entomologists Kevin Steffey and Mike Gray reported Thursday in the weekly U of I Extension Integrated Pest Management Bulletin that the highest numbers have been found by agronomists around central Illinois. Moth flights this spring have already resulted in armyworm damage, but the recognition of those May moths as armyworms didn't come until it was too late.

"...The numbers of armyworm moths being captured in pheremone traps in Pope County [Illinois] are noticeably larger than the numbers captured in April," Steffey and Gray reported Thursday. "The results from the early flights were pockets of significant armyworm damage in southern and Central Illinois in May. A few other reports from people who were not certain what moths they were seeing suggest that the moths in question were armyworms."

The dry weather conditions that have to this point ravaged the corn crop in Illinois will cause a shift in the placement and intensity of armyworm infestations. Egg-laying armyworm moths typically seek out areas with abundant foilage and residue.

"Given the very dry conditions throughout much of Illinois right now, armyworms are not going to find a lot of ideal egg-laying sites. The females are liable to concentrate their egg laying in fewer locations, resulting in concentrations of intense feeding," Steffey and Gray write. "No-till corn fields, green pastures, golf courses and possibly crops often not associated with armyworms will receive the brunt of the infestations."

The U of I entomologists continue, warning farmers to keep a close eye out for the moths. Just-hatched larvae are difficult to spot at first, making careful scouting key to avoiding economic losses.

"After larvae hatch from the eggs, their presence may not be noticed for a few days because the larvae are so small," Steffey and Gray write. "But when they get large enough, excessive damage may seem to appear overnight."

But, hasty diagnoses shouldn't be made without confirming whether invading moths are in fact armyworms. This can be a difficult task at times, according to Iowa State University entomologist Marlin Rice, especially when comparing armyworms to western bean cutworm moths, a pest that many agree will be making an appearance in the Corn Belt later this summer, if not already.

"There may be some confusion over misidentification of other moths that are now flying," Rice wrote in a recent edition of the ISU Extension Integrated Crop Management newsletter. "Several species are now being collected..., and if you are unfamiliar with the western bean cutworm, then these moths may present challenges for proper identification."

Armyworm moths can be identified by a small white spot in the middle of each wing with smaller dark markings on the back half of the wing. On the other hand, western bean cutworm moths have a cream-colored bar extending the majority of the outer edge of each wing.

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