Yield Response of Grain Sorghum to Corn Earworm and Fall Armyworm Infestation Density

The corn earworm, Helicoverpa zea (Boddie), and the fall armyworm, Spodoptera frugiperda J.E. Smith, are two of the most important insect pests of grain sorghum in the southeastern U.S. Recently, there have been concerns raised about the validity of the current action threshold for each species. The current threshold for both pests in Mississippi is one larvae per head. To address this issue, experiments were conducted in Stoneville, MS utilizing artificial infestations with second instar larvae of each species. Larvae were infested at seven densities ranging from 0.17 to 6 larvae per panicle and compared to an uninfested control. Additionally, corn earworm infestations were conducted at two plant densities. Plant density did not have an impact on feeding injury or yield losses from the corn earworm during 2013. Significant yield reductions compared to the uninfested control were observed for infestation densities of 0.5 or more larvae per panicle in the corn earworm trials and 0.25 or more larvae per panicle in the fall armyworm trials. These results suggest that the current threshold for each species may be too high, but these data are preliminary.