Early anthesis (Feekes 10.5.1; Zadoks GS60-61), characterized in wheat by the extrusion of anthers from florets in the middle third of the spike, is recommended as the optimum growth stage for fungicide application for Fusarium head blight (FHB) and deoxynivalenol (DON) management. This is largely because wheat spikes are most susceptible to infection by Fusarium graminearum, the causal agent of FHB, during anthesis and early grain fill. Early anthesis at the plot or field level is not a fixed point in time but rather a window that varies in length from a few to several days, but since it is necessary to define a fixed time during the anthesis window for fungicide application, early anthesis is often considered to be reached when approximately 50% of the primary tillers are at Feekes 10.5.1. However, practical limitations often make it difficult for producers to treat fields at early anthesis. Therefore, a series of studies were conducted to evaluate the efficacy of pre- and post-anthesis fungicide programs for FHB index (IND) and DON management, including single applications of the demethylation inhibitor (DMI) fungicides metconazole (Caramba) and prothioconazole + tebuconazole (Prosaro) at Feekes 10.5 (Zadoks GS59; spike fully emerged from the leaf sheath of the flag leaf) and a new Succinate Dehydrogenase Inhibitor (adepidyn/pydiflumetofen) + DMI (propiconazole) premix fungicide (Miravis Ace) at Feekes 10.3 (Zadoks GS55; spike half way out of the flag leaf sheath). Summary results from a quantitative synthesis of data from these studies will be presented showing that although pre-anthesis applications of Caramba, Prosaro, or Miravis Ace significantly reduced mean IND and DON relative to the nontreated check, in all cases, the overall mean efficacy in terms of percent control was substantially lower for the pre-anthesis timing compared to the early anthesis application. For Miravis Ace, a single pre-anthesis application was often just as effective as an early anthesis application against IND, but significantly less effective against DON. The economic consequences of pre-anthesis, relatively less effective, fungicide programs for FHB management in wheat will be discussed.         

ACKNOWLEDGEMENTS AND DISCLAIMER

This material is based upon work supported by the U.S. Department of Agriculture, under Agreement Nº 59-0206-4-018. This is a cooperative project with the U.S. Wheat & Barley Scab Initiative. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the authors and do not necessarily reflect the view of the U.S. Department of Agriculture.