Issue No. 13, Article 2/June 22, 2007
Increase Vigilance for Armyworms
(Originally published as an Alert on June 15, 2007)
We have heard from several people that extremely large numbers of armyworms have been observed and/or captured in traps. Kevin Black, insect/plant disease technical manager with Growmark, has observed "huge" numbers of armyworm moths in the Bloomington-Normal area, and several FS agronomists throughout central Illinois have reported to him equally large flights of the moths. Marlin Rice, Extension entomologist at Iowa State University, also reported "huge" numbers of armyworm moths captured in blacklight traps near Ames, Iowa. Ron Hines, FS seed agronomist for Growmark's southern region, has told us that the numbers of armyworm moths being captured in pheromone traps in Pope County are noticeably larger than the numbers captured in April. 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.
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. No-till corn fields, green pastures, golf courses, and possibly crops often not associated with armyworms will receive the brunt of the infestations. So this is a warning to everyone to keep their eyes open for armyworms everywhere. After larvae hatch from the eggs, their presence may not be noticed for a few days because the larvae are so small. But when they get large enough, excessive damage may seem to appear overnight.
On a related note to people who are operating pheromone traps to monitor for western bean cutworms: make certain you can differentiate between western bean cutworm moths and armyworm moths. The article in issue 12 of the Bulletin (June 15, 2007) provides some detail, and Marlin Rice has written an article for Iowa State University's Integrated Crop Management newsletter that adds more information.
We have no idea what will derive from the extremely large armyworm moth flights, but we should be on point.--Kevin Steffey and Mike Gray