Dual and Single Fungicide Application for Increasing Winter Wheat Grain Yield in Oklahoma.

Fungicide application timing on wheat plays a significant factor, not only for protecting the crop from foliar diseases but also maintaining yield potential. The objective of this study was to assess a dual fungicide application approach for increasing winter wheat grain yield in Oklahoma. A randomized complete block design with treatments arranged in a 2 × 4 factorial was implemented at two locations (Apache and Stillwater). Treatments consisted of two winter wheat varieties (Gallagher and Bentley), chosen based on the susceptibility and resistance to various fungal diseases, and four fungicide application treatments (non-treated control, fungicide applied at jointing (GS 6), fungicide applied at full flag leaf emergence (GS 9), fungicide applied at (GS 6 + GS 9). Leaf rust was the primary fungal disease observed at each location. At Stillwater, there was a variety × fungicide treatment interaction (P = 0.0163). For the variety Bentley, the dual application (GS 6 + GS 9) was the highest yielding fungicide treatment, yielding 1,760 kg ha^-1 over the non-treated control. The single fungicide treatments at GS 6 and GS 9 resulted in significantly less yield than the dual application, but both yielded substantially higher than the non-treated control (average of 580 kg ha^-1). The GS 6, GS 9, and GS 6 + GS 9 fungicide treatments applied to Gallagher showed an average yield increase of 970 kg ha^-1 over the non-treated control, but no difference in yield was found among those three fungicide treatments. Despite the leaf rust present at Apache, results indicated there was no variety × fungicide treatment interaction or significant differences among the fungicide treatments. Differences between the two varieties were the only significant effect. Preliminary results after the first year of this study indicated a significant positive yield response to a dual fungicide application was dependent on location and variety.