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Winter Wheat Crop in Great Shape, but Diseases Are Sneaking In

Stripe, leaf rust pathogens emerging in isolated areas; farmers should scout.

As a whole, heading into late April, the nation’s winter wheat crop is in as good shape as it has been for years.

Yet some faults are beginning to show, according to Erick DeWolf, Extension plant pathologist at Kansas State University.

In Oklahoma, Kansas and Nebraska – traditionally the nation’s largest region of winter wheat production – foliar diseases are beginning to show in isolated areas. In southwest Oklahoma, leaf rust has been spotted in a few areas, where the wheat has headed out, according to Bob Hunger, Extension plant pathologist at Oklahoma State University. "Foliar diseases are still at low incidence across Oklahoma but there is the indication that leaf rust is increasing across southern Oklahoma," he wrote in a report he writes each week. "Given the present and short-term forecast for temperature and moisture, I expect leaf rust to increase. These conditions also are favorable for stripe rust and powdery mildew, but the seeming sparseness of these two foliar diseases at this point in time indicates that in a typical year we are more at risk from leaf rust than we are from stripe rust or powdery mildew."

In central Kansas and southwest Nebraska, both stripe and leaf rust have been seen in isolated cases. The pathogens - pictured at right - are on the lower leaves, so not urgent yet. However, DeWolf and Hunger agree that caution is warranted and growers need to begin scouting. 

“I’m surprised we haven’t seen it sooner. I thought we might see elevated levels in Texas and Oklahoma,” DeWolf says. “That said, the finds of both stripe rust and leaf rust getting established prior to heading is cause for concern.”

The pathologist recommends wheat growers scout fields at least weekly to keep a close watch on fields for these diseases, both of which can be controlled with fungicide applications.  

“I wouldn’t say I’m exceptionally worried at this point. We’ve seen one report at this point. If we continue to see stripe rust or leaf rust increase in prevalence, move to the flag leaves, or to upper leaves as we approach heading stage, then we start getting worried,” he says. 

Stripe Rust and Leaf Rust in winter wheat.
University of Nebraska Crop Watch
One benefit of seeing rust this early in the season is that it gives growers time to apply fungicide, if necessary. 

The value of wheat doesn’t give wheat growers a strong incentive to invest in fungicide, DeWolf points out. “There may not be extra room in the budget to apply fungicides unnecessarily. So, it’s important to make good management decisions for rust diseases. Examine the varieties and susceptibilities, and continue to scout,” he says. 

As temperatures warm up, viral diseases are beginning to crop up, DeWolf adds. 

  • Soilborne Mosaic Virus is a viral disease, spread by a soilborne fungus, requiring soil moisture to thrive. Wet fall conditions like those that occurred in much of the Winter Wheat Belt in fall, 2018, have elevated the problem. There is no fungicide to control SBM. Rather, growers have to rely on varietal resistance. In the central portion of the Wheat Belt, resistance is built-in; however, growers in the western fringe of the Wheat Belt often don’t plant resistant varieties. “That’s where we’re starting to see elevated levels of soilborne mosaic,” DeWolf says. Symptoms of SBM include severely stunted and/or yellow plants in the spring. 
  • Wheat Streak Mosaic Virus is spread by the wheat curl mite, which can blow into new wheat from volunteer wheat or nearby green crops in the fall. Symptoms are green and yellow leaves. Growers tend to rely on resistant varieties because there is no chemical remedy. There are reports of WSMV in western Kansas and Nebraska. 

Crop Progress Reports

According to the April 14 Crop Progress Reports from National Ag Statistics, crop condition in key wheat growing states is: 

  • Texas: 51% good to excellent, with wheat turning color in southern Texas and heading out from the center of the state north. 
  • Oklahoma: 74% good to excellent, with wheat heading in southern Oklahoma and jointing in the northern part of the state. The crop is about a week behind the five-year average of progress. 
  • Kansas: 59% good to excellent, with the crop beginning to joint in southern Kansas. The crop’s progress is a week behind average. 
  • Nebraska: 68% good to excellent. 
  • Colorado: 62% good to excellent. The wheat crop is generally ahead of schedule based on a five-year average. 
  • Missouri: 40% good to excellent. 
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