The wheat crop in Ohio is now at or approaching Feekes 8 (flag leaf emergence), the growth stage at which we usually recommend fungicide application for foliar disease control. Conditions have been fairly cool and wet over the last 7 to 10 days, and will likely continue to be so over the next week, favoring the development of early-season diseases such as powdery mildew and Septoria. Septoria tritici leaf spot usually shows up first on the lower leaves as yellowish flecks that later develop into irregularly-shaped, brownish-gray lesions, with easily-seen dark-brown to black spots (called pycnidia) in the center. The disease is usually spread from the lower to the upper leaves by rain splash; so, if it rains and remain cool (50 to 68oC) over the next week or so, Septoria leaf spot will likely continue to spread.
Cool temperatures and high relative humidity are also required for the development of Powdery Mildew, another early-season disease that so is at very low levels so far this season. Typical symptoms of powdery mildew are whitish fungal growth (pustules) on the surface of leaves and stems. As soon as it begins to warm up, both Septoria and powdery mildew will become less of a concern, but continue to monitor your crop over the next several days. Remember, if the variety is susceptible and conditions become favorable, a fungicide can be applied to prevent the diseases from reaching the flag leaf (the upper-most leaf of the plant) before grain-fill. See the chart below for fungicide options and efficacy against common wheat diseases . Remember, always read and follow the labels.
Septoria tritici leaf spot on wheat – note the black dots (pycnidia) inside the lesion.
Powdery mildew on wheat leaf – as the name suggests, note the powdery, white pustules.