All counties in the south central and south west regions of PA are now at “High” to “Medium” risk for the development of scab in wheat and barley that is currently flowering. Our current weather forecast includes a few more days of wet, mild weather that is conducive to the production and spread of spores, and possibly more next week. 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. 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.
Wheat that is about 5 days or more past initial flowering cannot be treated. 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. Here is a chart to help tease out the best fungicide depending on what other diseases may be present in a given field: http://ces.ca.uky.edu/daviess-files/agriculture/NCERA_184_Wheat_fungicide_table_2011.pdf
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. A combination of choosing resistant wheat varieties, avoiding planting into corn or small grain stubble and residue management are also required to combat this problem long-term.
Keeping an eye on the FHB Risk Assessment Tool will become critical for those farmers who have wheat beginning to flower late this week and into the next two weeks. This forecasting site, at http://www.wheatscab.psu.edu/riskTool_2011.html, 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, which will occur sometime next month for most fields in the state. The extent of FHB in fields that begin to flower this week will not be evident until early to mid 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.