A Southern Wheat Rust Moves North

Two years ago, new strains of a major wheat disease appeared in the United States and overcame defenses that have protected most wheat in California and east of the Rocky Mountains in the past. This and other factors, notably cool and excessively wet spring weather in the Midwest for the past two years, have opened the breadbasket’s doors to wheat stripe rust.

This fungal disease had been relatively confined to the Gulf Coast, California, and the Pacific Northwest since the 1960s. It thrives in mild weather and is particularly dangerous to winter wheat in regions where wheat ripens before the summer heat arrives.

Wheat stripe rust caused yield losses of more than 7 percent in Arkansas last year and is expected to cause significant yield losses averaging 5 to 10 percent for winter wheat in Kansas and south Texas this year. In the past two years, stripe rust has also been reported for the first time in many years in Indiana and Ohio.

Plant pathologist Jim Kolmer at the Agricultural Research Service tracks wheat diseases for the ARS Cereal Disease Lab (CDL) in St. Paul, Minn. He has found the infections of stripe rust on winter wheat plots in St. Paul the highest in 35 years. Stripe rust has strips of bright-yellow rust infections aligned with the veins of wheat leaves. It can rapidly cover a plant and suck it dry.

The epidemic was also boosted by the two previous mild Gulf Coast winters that allowed the fungus to survive in greater numbers and spread north via spore showers in the wind.

David Long, a CDL plant pathologist, and colleagues make annual surveys of wheat fields from the Rocky Mountains to Ohio and from Texas to Georgia to check on rust severity. They collect more than 1,000 samples of infected leaves or stems and analyze them to identify rust species and strains. Those samples with wheat stripe rust are sent for identification to Xianming Chen, a plant pathologist at the ARS Wheat Genetics, Quality, Physiology, and Disease Research Unit in Pullman, Wash.

The CDL has a network throughout the United States and Canada to provide a heads-up to areas in the path of rust epidemics.