A yield-reducing fungus is attacking winter wheat fields across parts of the South and plant disease specialists are concerned it could soon spread north to Kansas, the nation's top-producing wheat state.

The disease, called stripe rust, is caused by the fungus Puccinia striiformis and often causes yield losses of around 40% on susceptible wheat varieties. It can destroy fields outright if not treated quickly with chemical fungicides.

The pathogen – which is spread by the wind and thrives in cool, damp weather such as what has predominated this spring – has been found in wheat throughout Louisiana and has even infected popular varieties thought to be resistant. Several cases of severe leaf rust and stripe rust were found in multiple locations around Texas during March, occurring in some hard red winter (HRW) wheat varieties previously thought to be highly resistant to the disease, such as Fuller, Santa Fe, Art, Overley, Jagger and Jagalene.

"The severity of the disease on varieties previously thought to be resistant is cause for concern," says Erick DeWolf, Kansas State University plant pathologist. "I believe these reports of stripe rust and leaf rust have important implications for wheat producers in Kansas. Fuller, Santa Fe and Art are all widely grown in central Kansas."

While no stripe rust has been yet reported in neighboring Oklahoma or Arkansas, stripe rust is likely lurking, says Gene Milus, plant pathologist, University of Arkansas Division of Agriculture. Wheat disease specialists are now working to determine if the outbreak is evidence of an underlying genetic mutation in the stripe rust fungus, which was once confined solely to the Pacific Northwest.

"We should get a much clearer indication of which varieties are vulnerable to stripe rust and leaf rust by the middle of April," says DeWolf. "At this time, I believe we have a moderate risk for severe stripe rust and leaf rust in Kansas. Growers should be investigating the potential costs of fungicides in case they need to respond to emerging disease threats in early May."