Watch out for Fall Armyworms

From Texas we are receiving reports of impressive fall armyworm buildups in wheat, turf and pastures. Fall armyworm is a tropical insect and overwinters only in the warmest areas of the U.S. As populations build throughout the summer, they move northward on weather fronts, often arriving in Oklahoma in late summer. Because several generations develop during the summer, the generations overlap and can effectively create a continuous supply of moths (and eggs). Any fall-planted wheat field that is emerging out of the ground could become infested. 
Fall armyworm infestations often go unnoticed for a while because they don’t cause obvious damage until they get bigger. The caterpillars shed their skin five times before they quit feeding. To indicate the stage of growth that a caterpillar is in, we refer to them as instars. The first instar is the caterpillar just after it hatches. A second instar is the caterpillar after it has shed its skin for the first time. A sixth instar has shed its skin five times and will feed, bury itself in the soil, and pupate.
If you were to ration out a supply of food to feed each instar, you would need to reserve 70% of the total supply just to feed a sixth instar caterpillar. It is similar to trying to feed a hungry teenager. Like a teenager, a sixth instar fall armyworm can eat lots of food in a relatively short period of time, and leave little leftover for anyone else.
Reports indicated that seedling wheat fields are suffering severe stand loss. These reports serve as an early warning for fall armyworm threats to Oklahoma wheat fields. Fall armyworms can kill seedling wheat, so newly planted wheat fields need to be watched carefully for several weeks after emergence. To scout for fall armyworms, examine plants in several locations within the field.  Fall armyworms are most active in the morning or late afternoon. Look for leaves that seem to have had  all of their green tissue removed which gives the leaf a “window pane” appearance. Examine some plants showing evidence of injury, and look in for small caterpillars in the whorl of the wheat seedling. When scouting, examine plants along the field margin as well as in the interior, because they often move in from road ditches and weedy areas. The suggested treatment threshold is 2 to 3 larvae per linear foot of row in wheat. In pasture, we do not have determined an established treatment threshold. However a general guideline developed for the southeastern U.S. suggests that two or three large larvae per square foot in grass pasture works as a treatment threshold.
It is much easier to control fall armyworms when they are small (less than ½ inches). Several insecticides are registered for control of fall armyworm in wheat, including Baythroid XL (cyfluthrin), Proaxis (gamma cyhalothrin), Cobalt (gamma cyhalothrin + chlorpyrifos), Karate/Warrior w Zeon (lambda cyhalothrin), Lannate (methomyl), methyl parathion, Tracer (spinosad) and Mustang MAX (zeta cypermethrin). Check Current Report; CR7194-Management of Insect and Mite Pests in Small Grains for more information on rates and products registered for fall armyworm control.
In pasture, Sevin, malathion, Lannate (for bermuda pasture only), Confirm2F, Tracer and methyl parathion are labeled for control of fall armyworm. Check Current Report, CR7193-Management of Insect and Mite Pests in Rangeland and Pasture for recommended application rates.
If you have questions concerning this topic or related topics, please contact the OSU Extension Center at 273-7683, stop by the office, or visit our website: http://countyext.okstate.edu/pottawatomie.