ALERT: Fall Armyworms May Reach Damaging Levels in Pastures Across Southern Illinois

Doug Johnson, University of Kentucky Extension Entomologist, has received reports of large densities of fall armyworms in pastures from central Kentucky to the Mississippi River. These infestations follow some large flights of these moths as reported recently by Professor Johnson. The fall armyworm is a tropical insect and the moths migrate to northern states during the late summer and early months of fall. Gulf Coast storms may increase the late summer flights northward. As female moths find grassy or pastured areas, they begin to lay eggs on grass blades. The life cycle (egg to adult) is temperature dependent and takes about 30 to 50 days to complete. Partially grown larvae overwinter in Gulf Coast states. Larvae currently feeding within pastures across southern Illinois counties will not survive hard frosts and the ensuing winter. However, their current feeding can still lead to significant damage to newly-seeded hayfields, pastures, wheat, and double-cropped soybeans. Double-cropped soybeans, if less than R6 stage (full seed) are most at risk when fields are adjacent to severely damaged pastures, especially the rows closest to pastured areas. Injury to plants typically occurs during the morning, late afternoon, or early evening hours. Densities of 5 to 7 larvae per square foot may cause economic damage to stands. Larvae that are 0.75 inches or less in length are easier to control. Those that are 1.25 to 1.5 inches long are the most damaging. Producers are encouraged to scout their pastures, double-cropped soybeans, and newly seeded hay or wheat fields. If fall armyworms are found in damaging levels, producers should consider a rescue treatment paying careful attention to harvest and grazing restrictions for the insecticide that is chosen for use.

Mike Gray