A cool, dark spring has slowed development of grains across the region and it shows in the progress of small grain development. This means barley and wheat are only now jumping up in much of the southern fields of the state. Fortunately, these weather patterns have also been unfavorable for the development of many of the fungal diseases we usually deal with. Powdery mildew, for instance, prefers temperatures between 60 and 75 degrees along with high humidity. We are just now beginning to see those conditions regularly. We generally recommend spraying for this disease only if 5-10% of the fully expanded upper leaves are infected, so if you are interested in adding a fungicide to a Palisade treatment, be sure to scout ahead of application to determine if it is necessary. It probably will not be necessary at this time.
Our most pressing concern right now will be preparing to control Fusarium head blight (a.k.a. head scab). If you intend to protect your barley from scab be prepared to spray a triazole fungicide at heading or shortly thereafter, which we could see in a few weeks. As many of you know, this is a disease of wheat and barley that can lead to the production of vomitoxin (DON) in grains.
For wheat, once it begins flowering, there is about a 5-6 day window to apply a fungicide. The labels state the last stage to apply is mid-flower and there is a 30 day to harvest restriction. Do not use any of the strobilurins (Quadris, Headline), or strobilurin/triazole (Twinline, Quilt, Stratego) combination products at flowering or later as there is evidence that they may cause an increase in mycotoxin production.
At this point in the season, the only way to reduce the scab problem is to spray. But in general, do not rely solely on fungicides, as they will provide at most a 50–60% reduction in scab severity and vomitoxin. Start with selecting resistant wheat varieties, and time sprays properly to achieve greater control.
Caramba or Prosaro are effective on scab and give control of most leaf diseases and glume blotch. They do not need to be tank mixed with another product to control these diseases. If either these products is unavailable, Proline and Folicur (which together provide the same chemicals as Prosaro) may be tank mixed at a rate of 3 + 3 fl. Oz./A. Spray nozzles should be angled at 30° down from horizontal, toward the grain heads, using forward and backward mounted nozzles or nozzles with a two directional spray, such as Twinjet nozzles. We anticipate a new active ingredient will be on the market for the control of scab soon, but it will not be labeled in time for the 2018 season.
If you choose to use a fungicide for these or any other diseases on wheat this year, the Fungicide Efficacy for Control of Wheat Diseases table has been updated for 2018.
Currently, PA is at a “low” risk of scab development because it has been so cool. But it doesn’t really matter what the risk is now because we are not close to heading. So as our season progresses keeping an eye on the FHB Risk Assessment Tool will become critical for those farmers who are trying to make the decision to spray or not.