A Southern Wheat Rust Moves North
August 1, 2001
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 breadbaskets 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.