We are starting to see fall armyworm (FAW) activity in corn and sorghum. Larvae feed down in the whorl of plants and, as these chewed leaves unfurl, plants can take on a ragged look. This defoliation is typically not of economic importance and thus treatments are not recommended. However, insecticide applications may be considered if feeding reduces leaf area by 30% or more and you are finding 1-2 larvae per plant, especially in drought-stressed fields. Later planted fields may suffer more damage when small plants are attacked. If you do decide to spray, keep in mind it is difficult to reach larvae, protected down in the whorl of the plant, with contact insecticides. By the time damage is noted larval feeding may be complete or nearly complete. Once mature, larvae crawl out of plants and pupate in the soil where treatments will not impact them.
We will have multiple generations of FAW and they may be of economic concern later in the season if they infest sorghum heads. At this stage, “headworms” (FAW and corn earworms) may cause approximately 5% yield loss per worm, per head. So, an average of one larva per head may lead to a 5% yield loss, two worms per head a 10% yield loss, and so on.
For more information on fall armyworms and other sorghum arthropod pests, please see: Managing Insect and Mite Pests of Texas Sorghum.
