Methods of infestation, damage and economic injury level for fall armyworm, Spodoptera frugiperda (J. E. Smith), in Mississippi grain sorghum

Studies were conducted at the Mississippi Agricultural and Forestry Experiment Station Plant and Soil Science Research Farm during 2002 and 2003 in order to determine methods of plant infestation and effect on survival of fall armyworm larvae on grain sorghum, and to identify damage levels and a probabilistic economic injury level for this pest on whorl stage sorghum. The application of third instar larvae reared on wheat germ based diet using a hand held plastic device to transfer the larvae mixed in corn cob grit during early morning or early evening was deemed to be effective in establishing populations of this pest under field conditions.; Fall armyworms reduced yield only when plants were infested at an early growth stage (5 leaf stage). This information, along with the cost of insecticide application and market value of the crop, was included in the conventional economic injury level formula to develop a probabilistic economic injury level for three sorghum growth stages using Monte Carlo simulations. Results indicate that the economic injury level for growth stage 2 (5 leaves) sorghum is approximately one larva per plant, which is the value used in Mississippi as economic threshold for this pest. Simulations performed for growth stage 3 (8 and 10 leaves) indicate that the economic injury level should be established at 2.5 and 3.9 larvae per plant, respectively, justifying again the recommendations provided by the Mississippi State University Extension Service. The development of these injury levels is considered important for current day recommendations for control of this pest on sorghum because the origin of the currently used threshold in Mississippi is unknown.