The rain that was forecast earlier in the week did not manifest. However, current forecasts are calling for an 80% chance of heavy rain on 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). Applications to fully headed fields may have some efficacy, but it is not likely to be optimal. Sparse data exist on heading applications and until we have a more complete picture I do not recommend them. 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 around 42-45% suppression of DON when applied within that 5 day window of the start of flowering unless they are applied to a moderately resistant variety, in which case 75% control is achievable.
--Nathan Kleczewski, Extension Specialist, University of Delaware
For more details, go to the FHB Risk assessment tool at http://www.wheatscab.psu.edu