Small Grain Disease Update – May 6, 2011

Bob Mulrooney, Extension Plant Pathologist;

Be sure to keep scouting for the presence of diseases, especially powdery mildew, at this time. With the return of cooler temperatures and risk of showers and cloudy weather as well, powdery mildew could become a problem, especially in very thick stands of susceptible wheat. It is important to keep the uppermost two leaves as free of diseases as possible to protect yields. At the most, you can wait until you see 5-10% of the upper two leaves infected before applying a fungicide. Tilt, Stratego, Twinline, and Quilt can be applied as late as heads emerged but not yet flowering. If scab should be a concern this year it may be best to use only a triazole fungicide at heading through flowering to avoid mycotoxin issues if scab infection occurs. There is evidence that if fungicides containing strobilurins (Quilt, Twinline, Stratego) or strobilurins alone are applied during heading up to flowering, they can increase mycotoxin production if scab occurs during flowering. If a fungicide is needed as late as flowering for powdery mildew, Septoria leaf blotch, tan spot, or other disease and conditions are favorable for scab development consider applying Prosaro, Caramba, or Folicur for scab suppression and control of the other diseases just mentioned. For a table that rates the efficacy of fungicides for use on wheat diseases see the following link to the Kansas State fact sheet with the NCERA-184 ratings. This is a group of wheat pathologists from across the country that collaborates on wheat disease control.

Head Scab Risk Assessment Tool
Scab is still the one wheat disease that can cause major economic losses if weather conditions are favorable prior to and during flowering. The tools that we have to manage scab are limited but the use of rotation, resistant varieties and fungicides can help reduce the losses from scab should it appear. One of the tools that we have to help predict its occurrence and aid in making fungicide application decisions is the Head Scab Risk Assessment Tool that is found on the wheat scab website The site provides information on how to use the tool and its limits.


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