Powdery mildew beginning to appear 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
Powdery mildew is beginning to show up on wheat in Michigan. Wheat is currently at Feekes 5 around Isabella County, and at Feekes 6-7 (first to second node) for most other parts of the state. It is not uncommon to see powdery mildew low in the canopy, early in the season. Current temperatures are in the favorable range (around 59-72°F) for this disease. Often, mildew stays low in the canopy and does not cause significant loss to yield. Powdery mildew is more of a concern if it continues to climb and gets up on the flag leaf. If you are seeing it now, continue to monitor your fields and evaluate the level of infection at flag leaf to the boot stage. In general, the threshold for fungicide treatment is two to three powdery mildew spots per leaf on the leaf just below the flag leaf, (averaged over 30-50 leaves sampled randomly in the field).
In the April 26 Field Crop CAT Alert, Management of foliar wheat disease, Part 2, is a rating table of fungicides evaluated for effectiveness against powdery mildew, and the growth stage limitations for applying certain fungicides. You can check the MSU variety trials ratings (http://www.css.msu.edu/varietytrials/) to get an idea of how your variety performed in statewide university trials, and use your own field experience with a variety to determine how susceptible it is to mildew. The variety trial ratings for powdery mildew are scored from 0-9, with (0 the lowest amount of mildew, to 9 the highest) There is a yearly, two year, and three year average score. Looking at the average rating over several years will give you a better idea of performance than looking at a single year.