Evaluating soybean planting date and at-planting insecticide as a management strategy for Resseliella maxima (Diptera: Cecidomyiidae).

Soybean gall midge (Resseliella maxima Gagné) was confirmed in 2019 as a new species in the Midwestern United States. It is known to occur in seven states (Iowa, Kansas, Minnesota, Missouri, Nebraska, North Dakota, and South Dakota) and can cause up to 100% yield loss in soybean (Glycine max (L.) Merr.) for the first 30 m from the field edge. Field and greenhouse observations indicate R. maxima infests soybean stems through fissures at the base of the plant during early vegetative growth stages. Given the importance of plant stage for infestation and the limited knowledge on chemical control, a field study was conducted across four locations in eastern Nebraska to evaluate the combined effects of planting date and an at-plant insecticide on R. maxima infestations, plant injury, and grain yield. To test these effects, the study was conducted as a randomized complete block split-plot design with 3 planting dates (late-April, mid- and late-May) assigned to main plots and 2 insecticide treatments (phorate applied at planting and untreated control) assigned to sub-plots. To assess treatments, the proportion of infested plants, larval abundance, plant injury, and yield were recorded. Results showed a significant difference in the proportion of infested plants, larval abundance, plant injury, and yield among treatments. However, treatment differences varied among locations. This study enhances the understanding of R. maxima management by demonstrating how integrating planting date and at-planting insecticide use can reduce plant injury from this emerging pest.