Fusarium head blight (a.k.a. head scab) is a disease of wheat and barley that can lead to the production of toxins in grains.
The fungus that causes this disease enters through the flowers and infects the developing grain. Warm, humid environmental conditions at wheat or barley flowering favor the development of this disease.
Most counties of PA are now at a “Low” risk for the development of scab in wheat and barley that is currently flowering. Our current weather forecast includes a chance of rain later this week, so certain areas may have weather that is conducive to the production and spread of spores. Be prepared to spray a fungicide on fields that are at medium to high risk at flowering. Remember, sprays applied PRIOR to flowering will NOT provide significant suppression of scab or toxin production. Caramba, Proline 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 these products are 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.
Once wheat begins flowering, there is about a 5-6 day window to apply a fungicide. The labels state the last stage of application 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. 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. Choose resistant wheat varieties, and time sprays properly to achieve greater control.
Keeping an eye on the FHB Risk Assessment Tool will become critical for those farmers who have wheat beginning to flower in the next few weeks. This forecasting site is an online model that helps us predict infection risk levels everywhere in the state. Visit it at your convenience, or sign up to have updates e-mailed or texted directly to you. The maps on this site update at approximately 10:15am daily, so check back if you receive a “No Data” message.
The full extent of symptom expression is usually evident 21 days following infection, so, approximately three weeks after flowering. Symptoms include bleached kernels (called tombstones) that are distinct from healthy green tissue (Figure 1). The level of scab in fields that begin to flower this week will not be clear until mid to late June. Since fungicides do not completely protect the plant, and fields that are past flowering can get some infection, it is recommended that areas that are designated as medium to high risk be harvested with a high fan speed on the combine. This will clean out some of the infected seed that tends to be lighter and will reduce the toxin level in the final product.
Source : psu.edu