Cool weather and moisture after flowering often means extended grain-fill and high yields, especially when disease levels are as low as they were at the time of pollination and early grain development in some fields. However, excessive rainfall associated with the cool temperatures could increase the severity of diseases that thrive under cool conditions. But with the crop now well into grain-fill and even turning in some locations, there is very little you can do about late-season diseases. The pre-harvest interval for some of the best fungicides is 30-45 days, which mean that they are now off-label in most areas, given that harvest will likely begin in less than 30 days.
If you did apply a fungicide at heading or flowering, that should have helped to delay disease spread within the field and up the plant, minimizing grain yield and quality losses. There are still lots of fields out there with healthy flag leaves, and by the time those leaves eventually become diseased, the yield would have already been made. An application of Prosaro or Caramba at heading (for barley) or flowering (for wheat) would have also helped to reduce head scab and vomitoxin. But since these fungicides only suppress the disease, you may still see some scabby heads in your field. Now is the time to walk those fields to see if head scab is present and how much – this will help you to plan your grain harvest and handling strategies.
Consider harvesting fields with moderate levels of head scab (5-10% incidence; that is, 5 to 10 heads out of every 100 with some scab) at the very first dry-down (18-22% moisture). Harvesting early will reduce problems with sporting and further contamination with vomitoxin, once the grain is dried (13-15% moisture) and stored. You should also increase your combine fan speed to blow out scabby, light-weight kernels. We have found that increasing the air flow through the harvester can reduce scabby grain by an average of 40% and vomitoxin by an average of 17%.