Septoria tritici leaf spot on wheat. Photo by OSU Extension.

Watch for early wheat diseases

By Pierce Paul, Ohio State University Extension plant pathologist

The wheat crop in Ohio is now between early boot (Feekes 10, in the south) and approaching Feekes 8 (flag leaf emergence) in northern counties. Cooler-than-usual conditions over the last few weeks have slowed the crop down considerably, but as temperatures increase, the crop will advance through several growth stages over a relatively short period. Cool conditions have also kept foliar diseases in check, but Septoria, and to a lesser extent, powdery mildew are still showing up in some fields. Septoria tritici leaf spot is favored by cool, wet conditions similar to those experienced over the last several weeks. It 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. Cool temperatures and high relative humidity are also required for the development of powdery mildew. Typical symptoms of powdery mildew are whitish fungal growth (pustules) on the surface of leaves and stems. If the variety is susceptible and conditions continue to be favorable, a fungicide application may be warranted to prevent both diseases from reaching the flag leaf before grain-fill.

Most of the fungicides commonly used on wheat are rated as very good or excellent against Septoria and good or very good against powdery mildew. 

Remember, always read and follow the labels when making an application. For both diseases, a single application between Feekes 8 and Feekes 10 would be sufficient to protect the flag leaf and minimize yield loss. However, applications made at these early growth stages will not provide adequate control of late-season diseases like head scab and Stagonospora glume blotch. So, you should scout fields before making your fungicide application decisions. If powder mildew and Septoria levels are low as the crop approaches heading (Feekes 10.5), you may be better off waiting to treat fields at anthesis (Feekes), as this will help to suppress head scab, which is still the most damaging and important disease of wheat in Ohio, while at the same time provide very good control of Septoria, powdery mildew, and late-season diseases such as Stagonospora and rust. 

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