Hessian Fly (Diptera: Cecidomyiidae) Injury and Loss of Winter Wheat Grain Yield and Quality

Abstract

The damage–yield-loss relationships of Hessian fly, Mayetiola destructor Say, in soft red winter wheat, Triticum aestivum L., were examined using results of studies on Hessian fly management and yield loss that were conducted over a 9-yr period with various cultivars and planting times and at various locations in Georgia. Differences in grain yield and test weight of susceptible and resistant cultivars with or without a systemic insecticide (disulfoton or phorate) at planting were compared with the percentage of infested tillers in autumn (vegetative stage) and the percentage of infested stems or the number of immatures per stem in spring during grain filling. Grain yield loss increased linearly with increasing percentage of autumn-infested tillers and spring-infested stems. Infestations had little effect on grain test weight until infestations exceeded 20% of autumn-infested tillers or 38% of spring-infested stems. Grain yield and test weight losses were exponentially related to number of immatures per stem during grain filling, with proportionate loss increasing as immature numbers increased up to 6 immatures per stem. Analysis of grain yield components of headed stems found that injury reduced seeds per spike, spikelets per spike, seeds per spikelet, and seed weight. Gain thresholds indicated that, depending on commodity price, an application of a systemic insecticide at planting provided positive marginal returns for 68–74% of plot-years (n = 50) on susceptible cultivars but only provided positive returns for 23–27% of plot-years (n = 26) on resistant cultivars. Depending on control cost, economic damage occurred when autumn infestations exceeded 5–8% of infested tillers or when spring infestations exceeded 13–20% of infested stems, or 0.4–1.0 immatures per stem. These results provide a quantitative basis for Hessian fly damage loss assessment in wheat.