Current forecasts are calling for an 70-80% chance of heavy rain on Thursday-Friday. Fields entering flowering around this time will likely be at risk for scab. You have a 5-6 day window from the start of flowering (Feekes 10.5.1 yellow anthers from the center of heads) where fields are most susceptible and fungicides are most efficacious for suppression of vomitoxin (DON) IF conditions favorable for development of FHB occur. The best fungicides for DON suppression are Prosaro, Caramba, and Proline. Do not use fungicides containing a strobilurin active ingredient (e.g. Quilt, Aproach Prima, Stratego, Headline, Quadris, etc.) as strobilurins have been associated with increased DON levels when applied to heads. Remember that fungicide use gets you on average 42-45% control of DON when applied within that 5 day window of the start of flowering AND the environment is conducive for disease. If recommended fungicides are applied to a moderately resistant variety over 70% control may be achievable. Prosaro, Caramba, and Proline will also control common foliar diseases.
--Nathan Kleczewski, Extension Specialist, University of Delaware
For more details, go to the FHB Risk assessment tool at http://www.wheatscab.psu.edu