Ric Bessin, UK Entomologist, warns reports of economic infestations of fall armyworm infesting sweet corn and late-planted field corn are coming in from multiple counties this week. Extension specialists from states to our south have described high populations of fall armyworm earlier in the year than is typical, so we need to watch for increasing numbers, particularly in southern and western counties as the summer progresses. It has been quite a few years since we have had fall armyworm populations that have arrived early enough to threaten corn. This is also compounded by the wet spring and cool early summer which has delayed corn development and kept fields vulnerable to fall armyworm egg laying longer into the summer.
Fall armyworm can be a very difficult to control pest if infestations are not treated when the larvae are small. After the larvae reach approximately ¾” in length, they can form a frass plug in the whorl of the corn plant that reduces the ability of insecticides to contact the larvae. There are a number of insecticides that can be effective when applied while the larvae are small (See ID-36 for sweet corn recommendations: http://www.ca.uky.edu/agc/pubs/id/id36/id36.htm).
Growers should be monitoring their corn fields, particularly all of their later plantings (read that as late May and later). Some Bt corn hybrids for corn borer control only provide suppression of fall armyworm, so these fields will need to be monitored as well.
For more information on fall armyworm in corn, read ENFACT-110, http://www.ca.uky.edu/entomology/entfacts/entfactpdf/ef110.pdf