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Winter Wheat Watch: Rust Spreads North into Nebraska
In general, the winter wheat crop is in good shape from Texas north to Nebraska. But incidents of stripe and leaf rust have growers concerned about what could happen as the crop heads into the 2016 homestretch.
Last week, Extension specialists at University of Nebraska-Lincoln (UNL) found trace amounts of leaf rust in several fields in Nuckolls County, along the Kansas border. Stripe rust has been found in northern Kansas and northwestern Colorado. The diseases are being pushed northward by south winds that have hammered the Wheat Belt the last couple of weeks. "Growers should scout fields for early disease detection and be prepared to apply a fungicide if presence of stripe rust, leaf rust, or both is confirmed," says Stephen Wegulo, Extension plant pathologist at UNL.
Stripe rust pustules are yellow and appear on the upper leaf rust. Before jointing, young leaves typically don't form stripes. Instead, the stripe appearance occurs on older leaves. Leaf rust pustules, on the other hand, are orange-brown and randomly distributed on the upper leaf surface.
In the case of stripe rust, Erick DeWolf suggests growers check fields as the crop approaches flag leaf emergence and heading. "Fields with stripe rust still in the lower canopy at heading are at moderate risk for severe yield loss. This means fungicide applications are likely to result in profitable yield response (greater than 4 bushels per acre) 50% to 60% of the time," he explains. Fields with high risk for severe yield loss have the disease established on the upper leaves prior to heading. Fungicide applications in those cases will result in profitable yield response 60% to 90% of the time.
Growers farther north still have time to apply an early-season fungicide, which should take place at Feekes 5 (leaf sheaths strongly erected) to Feekes 6 (when the first node on the main tillers is visible). The late-season, or flag-leaf application, should occur when the flag leaf is 50% to 100% emerged. The flag leaf contributes most to the grain fill. Research at Kansas State University indicates that the flag leaf application does the most good of the two treatments.
Growers should consider fungicide application when it is economically viable to do so. Fields with low yield potential may not benefit from a fungicide application.
There are two publications you may want to check out:
- Fungicides and Their Efficacy Ratings on Various Wheat Diseases
- Evaluating the Need for Fungicide in Wheat
In its April 4 Crop Progress Reports, USDA's National Ag Statistics Service reports wheat in Texas is rated 11% excellent and 36% good. In Oklahoma, it is 10% excellent and 51% good; Kansas, 7% excellent and 48% good; and Nebraska, 9% excellent and 51% good.