Favorable environmental conditions may allow scab development over a wide window following head emergence of small grains. However, fungicides can’t be applied too late in the growing season, because each fungicide has a pre-harvest interval that prohibits later application. The shortest preharvest interval for registered fungicides is 30 days. Research has shown that the optimal timing for fungicide application under current registration laws is:
Hard Red Spring Wheat: Optimum time to apply a single fungicide for scab and DON reduction is at early flowering, equal to Feekes 10.51. Applications prior to this growth stage have not adequately reduced scab severity or DON.
Durum Wheat: Optimum time to apply a single fungicide for scab and DON reduction is at early flowering, equal to Feekes 10.51. However, durum has a long window of vulnerability to infection, from early flowering (Feekes 10.51) through kernel watery ripe stage (Feekes 10.54). Because of that, a slightly later application than early flowering may be feasible, if environmental conditions are more favorable for disease development just past flowering.
Spring Barley: Optimum time to apply a single fungicide for scab and DON reduction in spring barley is at early full head emergence, equal to Feekes 10.5. Later applications or split applications in barley also may be successful, if barley prices and fungicide prices allow economic application with two treatments.