Warning, Armyworms Spotted in Pastures!

Doug Johnson, Extension Entomologist, University of Kentucky

Fig. 1. Armyworm

Capture of armyworm (AW) in the IPM pheromone baited traps still remains below average. Nevertheless, this does NOT mean that there are no AWs around. While economically important populations of AW are not (yet) a wide spread problem this year, the fact remains there certainly are infested fields. The question becomes which fields are infested with an economically important population size? There is only one way to know that, and that is to scout. We do know that AW feeding on pasture grass has been reported from Butler Co. and I expect, that if one looks, infested fields will be found in other areas.

Fig. 2. Fall Armyworm

Do not confuse armyworm with fall armyworm or for that matter beet armyworm, army cutworm etc. These common names can be misleading as they sound similar but represent completely different insect species, whose ’ common features are only that they often move in large masses (hence the descriptor “Army” worm) and they feed on similar plants,generally grasses such as pastures, and large grasses such as wheat, corn, sorghum, and millet.

Most often confused in Kentucky are armyworm and fall armyworm. Armyworm also called “True armyworm” is a spring pest for Kentucky and most of the eastern U.S. It overwinters as far north as Tennessee and probably southern Kentucky, then migrates northward in the warm months. Fall armyworm (FAW) is a late summer to fall pest in Kentucky. This is due to its’ inability to tolerate cold weather, requiring it to overwinter in Texas, usually south Texas, then migrate to Kentucky and northward in the warmer months. During our current time of year armyworm is the threat to pastures, wheat and corn.



Generally speaking, by this time of year, wheat is close enough to harvest that armyworm are not going to do much economic damage UNLESS they are clipping heads. Head clipping and worm feeding on the Flag and F1 leaves is the only really important damage. Control is generally warranted in wheat if 16 armyworms per four square-foot sample are found. If control is necessary, products may be found in ENT-47, Insecticide Recommendations for Small Grains (Barley, Oats, Wheat)- 2013.

Pastures could be damaged, but if growing conditions are reasonable, pastures will usually outgrow major damage. Thresholds are not well established but if an infestation does occur especially as pasture is being cut for hay, the producer should keep an eye on the regrowth. If satisfactory regrowth is occurring, and predicted weather is suitable for pasture growth, control may be avoided. If an insecticide application is warranted, products may be found in ENT-17, Insecticide Recommendations for Alfalfa, Clover and Pastures -2013. If animals are on the field, producers / applicators are cautioned to check the product label to determine if animals have to be removed from the field before application and if so, for how long.

NOTE: Do not confuse these insects with Eastern Tent caterpillar (ETC). Eastern Tent caterpillar is associated with Mare Reproductive Loss Syndrome but these two armyworms are NOT associated with this syndrome.

This year because of our long period of planting, corn may be the major plant at risk of armyworm. In addition, very late planting especially in far west Kentucky could lead to problems with Fall armyworm (but more on that story later). However, most producers are planting corn products that contain transgenic “B.t.” insect toxins. Most of these products will have good protection from armyworm. If you are planting a product that allows Refuge in a Bag (RIB) you might only notice armyworms if you see damage on the 5-10% scattered Refuge plants (those without the B.t. toxin). If you are planting a product that requires a block refuge (non- B.t. plants) or for other non-B.t. containing corn like certain food grade corns or sweet corn, you should be scouting for armyworm now! If control is warranted, corn insecticides may be found in ENT-16, Insecticide Recommendations for Corn-2013.

Insecticide Recommendations may be obtained from your County Extension Office or on line at:
http://pest.ca.uky.edu/EXT/Recs/welcomerecs.html