Powdery mildew is showing up on wheat

Seasonal considerations for controlling powdery mildew and other wheat diseases.

Usually we expect powdery mildew after a prolonged period of cool wet weather later in the spring or early summer. However, powdery mildew has already appeared on susceptible wheat varieties (Photo 1). The disease may spread due to the early presence of inoculum and favorable weather. Although not the most aggressive foliar disease of wheat, it should not be underestimated. Hot, sunny, dry weather will stop the fungus from progressing up the plant onto the flag leaf, especially if the variety has reasonably good resistance. However, in wet weather, the disease can easily continue up onto the flag leaf – and even the head – and cause losses of at least 10 bushels/A. Lesions of Stagonospora nodorum were also evident on the lower leaves.

Powdery mildew on wheat.
Photo 1. Powdery mildew on wheat.

Growers contemplating the use of a fungicide might consider the following:

  • Varietal resistance will matter in seasons such as this. The most resistant varieties will not be affected by powdery mildew and will suppress the disease, but the majority of popular varieties are fairly susceptible and will likely need to be protected.
  • Those electing to treat for mildew prior to heading should also target leaf spot and rust diseases. Fortunately, the recommended materials will generally do well against all the commonly occurring foliar disease. Prior to heading, growers could use any of the products listed, however, once the head has emerged, products containing a strobilurin should be avoided as it has been shown that DON production may be enhanced by this fungicide group.
  • If a recommended fungicide was used at tillering and has suppressed powdery mildew, a fungicide application could be postponed until early flowering so that Fusarium head blight can also be targeted with a single application of fungicide. For broad spectrum protection, preference should be given to Prosaro or Caramba or, as second best, one of the tebuconazole products.

Management of small grain diseases: fungicide efficacy for control of wheat diseases (revised 4-6-11)

The North Central Regional Committee on Management of Small Grain Diseases (NCERA-184) has developed the following information (see Table 1) on fungicide efficacy for control of certain foliar diseases of wheat for use by the grain production industry in the U.S. Efficacy ratings for each fungicide listed in the table were determined by field testing the materials over multiple years and locations by the members of the committee. Efficacy is based on proper application timing to achieve optimum effectiveness of the fungicide as determined by labeled instructions and overall level of disease in the field at the time of application. Differences in efficacy among fungicide products were determined by direct comparisons among products in field tests and are based on a single application of the labeled rate as listed in the table. Table includes most widely marketed products, and is not intended to be a list of all labeled products.

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