Cereal stem rust widespread in eastern Washington, north Idaho

SPOKANE, Wash. – Harvest is in full swing across eastern Washington and northern Idaho. Farmers are optimistic about spring wheat and barley yields following unusually high rainfall during the summer.

“Some growers, however, may see a dark cloud rise above their grain combine – and it won’t be from the exhaust,” said Diana Roberts, a Washington State University Extension specialist. “The culprit is stem rust – a fungus that infects cereal crops late in the season and often goes unnoticed until harvest, when black clouds of spores erupt as the crop is threshed.”

Stem rust on wheat stem and leaf. Click image for a high-resolution version.

Farmers are familiar with stripe rust, which has been a major problem in the region. Stripe and leaf rusts infect wheat leaves primarily. Stem rust is caused by a different fungus; as its name suggests, it infects the plant stems as well as leaves.

“We have a website that has photos and information on identifying and managing stem rust,” Roberts said.

Late rains to blame

“This year scientists have found cereal stem rust widespread in Whitman County, especially north of Colfax and Palouse,” reported Mike Pumphrey, WSU spring wheat breeder. “We also found the disease in Spokane and Stevens counties in Washington and Latah County in Idaho.”

“The problem is due to late season rain, which we do not get very often in the Inland Northwest,” said Xianming Chen, a U.S. Department of Agriculture plant pathologist at WSU. “Sometimes stem rust causes total crop loss.”

“Stem rust is most severe this year in late-seeded barley crops, though many spring and winter wheat fields are affected,” said Kevin Murphy, WSU barley breeder.

The good news is that the stem rust population in our region is not the race group called Ug99, which was first detected in Uganda in 1998 and has spread to the Middle East and South Africa, said Les Szabo and Yue Jin, USDA scientists from Minnesota. Ug99 is virulent against many resistance genes, some of which previously protected wheat against stem rust.

“By now it’s too late for farmers to spray for rust in their crops,” Chen said. “But we recommend that they select resistant varieties for next season and avoid planting spring crops late.”

Eradicating host barberry

The stem rust pathogen is unique because, in order to complete its life cycle, it needs an alternate host – the common barberry plant Berberis vulgaris. Japanese barberries used in landscaping do not host stem rust.

Stem rust on common barberry, the alternate host. Click image for a high-resolution version.

Settlers introduced the common barberry, and the shrub typically is found near old homesteads. During the last century, the USDA conducted massive programs to eradicate common barberry; however, barberry plants are regrowing and stem rust is recurring in the wetter parts of the Inland Northwest.

“Alternate host plants near a wheat or barley field are crucial for early season stem rust infection,” said Tim Murray, WSU plant pathologist. “If farmers find and eradicate common barberry plants near their fields, they will prevent the rust from spreading field-to-field later in the season.”

WSU asks farmers to report problems

“WSU wants to know if farmers find stem rust in their fields so we can determine the extent of the problem,” said Roberts. “There’s a tab on the stem rust website where you can enter information about affected fields. You may also go there for more detailed information about stem rust and how to eradicate barberry.”

For more information, go to the website or contact Diana Roberts at WSU Spokane County Extension, 509-477-2167 or robertsd@wsu.edu.