Powdery mildew on wheat
Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.
Wheat growth in some areas of the state is at flag leaf or fast approaching it. The flag leaf is responsible for 60 to 70% of the photosynthate needed for grain development. With Wednesday’s heavy rainfall (May 10), forecasts of additional precipitation for the next few days and resulting high humidity, it’s probably a good time to mention powdery mildew. A powdery white growth of mold on the leaves is symptomatic of powdery mildew. High humidity and temperatures in the 60 to 75 degree range are favorable for its development. Many of the wheat varieties grown in Michigan are moderately to highly resistant to powdery mildew, but finding information about the susceptibility of different wheat varieties can be difficult. The Michigan State variety trials site lists a number of white and red wheat varieties and two year ratings for powdery mildew at the link listed below http://www.css.msu.edu/varietytrials/wheat/PDFs/2005_YT_Report_Final.pdf
Another site to check is Ohio State’s listing at: http://www.oardc.ohio-state.edu/ohiofieldcropdisease/wheat/Wheatreactions05.htm
If the varieties you have planted are resistant to mildew, then fungicides are not usually economical for the management of powdery mildew. Even if the varieties you have planted are listed as resistant, it’s a good idea to scout your fields to keep an eye on mildew and other leaf diseases. Fungal populations can change and overcome resistance over time. Scouting for powdery mildew should take place at flag leaf emergence (Feekes 8) and boot stage (Feekes 10). Check 50 individual tillers at random throughout the field. The threshold for fungicide application is 2 to 3 lesions (about 1% of the leaf area) on the leaf below the flag leaf.
Products registered in Michigan for management of powdery mildew on wheat include: Headline, Propimax, Quadris, Quilt, Stratego and Tilt. Two lower- risk products also registered include Armicarb (Potassium bicarbonate) and Sonata (a biofungicide).
Check the label for rates, reentry intervals and preharvest intervals. This information is provided only as a guide. It is the responsibility of the pesticide applicator by law to read and follow all current label directions. No endorsement is intended for products listed, nor is criticism meant for products not listed.