Nathan Kleczewski, Extension Specialist – Plant Pathology; nkleczew@udel.edu
Things remain dry and fairly warm, which means that a low scab risk is likely for the majority of areas in Delaware. Remember that most of the spores (roughly 70%) for head scab “rain” from the air at night when the wind calms down. These spores are supplied from the region. We see high scab risk develop when there are heavy rains on a regional scale in the days before flowering. This rain allows the fungus in the residue to grow, produce spores, and launch these spores into the air currents. Consequently, I expect the early flowering wheat will be fairly clean as far as head scab and vomitoxin. Wheat that flowers later next week or soon thereafter may still have some risk of scab, depending on if we receive any significant rain. Keep watching the wheat scab prediction center website for updates: http://www.wheatscab.psu.edu/. Remember that the site only updates once and that this occurs after noon, so it’s always best to check it later in the afternoon or evening.
With the lack of rain, there have been some questions about irrigating wheat and the impacts it may have on FHB. In general it is best to fill the soil profile as best as you can before full heading. If possible, try to irrigate during the day to allow the heads to dry before dusk. Irrigation at night could potentially contribute to head scab by moving larger, residue borne spores to the heads and provide additional moisture of the heads, allowing for higher levels of infection. I wouldn’t recommend irrigation after flowering; however, if you plan on applying a scab fungicide and irrigating after flower it is best to apply the fungicide before irrigating the field.