Winter wheat virus gaining foothold in northern Idaho

By John O’Connell

University of Idaho

MOSCOW, Idaho -- A tough-to-manage disease affecting winter wheat that was confirmed for the first time in the state last spring has recently surfaced in several more northern Idaho fields, according to two University of Idaho crop experts.

Kurt Schroeder, UI Extension cropping systems agronomist, and Doug Finkelnburg, UI Extension educator of cropping systems, alerted farmers and agronomists last spring that a couple of fields in Nez Perce County were infected with soilborne wheat mosaic virus (SBWMV).

The disease, which spreads via tainted soil and can significantly reduce yields within infected patches, was found this spring in additional fields in Nez Perce County, as well as four Idaho County fields.

“Those four fields in Idaho County are not contiguous. There is some distance between them,” Finkelnburg said. “We suspect it’s very likely there are additional fields we haven’t discovered yet.”

SBWMV was first found in the central plains of the U.S. in 1919 and arrived in Oregon’s Willamette Valley in 1994. In 2005, the disease was confirmed in Oregon’s Columbia Basin, and it arrived in Walla Walla County, Wash., in 2009.

Schroeder and Finkelnburg sought to raise awareness among their region’s growers and fieldmen about SBWMV symptoms and how to respond to confirmed infections during field days, cereal schools and other industry forums throughout last season.

The virus replicates in cool, wet conditions, often infecting crops in the fall when temperatures drop below 60 degrees.

SBWMV is easily confused with other common problems affecting cereals, such as barley yellow dwarf virus, excessive moisture and nitrogen deficiency.

Upon emerging from dormancy, infected patches appear light-green or yellow and their growth remains stunted for a while compared with surrounding healthy plants.

The patches can appear to recover as temperatures warm, but plants still suffer yield losses. Laboratory testing is needed to confirm the disease.

“There is a high probability because it’s so easily confused with other common problems that this has gone unnoticed for some time, and once we had a positive detection last year and we did a concerted education effort to describe the symptoms and get the word out, I believe we had some success in education and outreach and people started to look for it specifically,” Finkelnburg said.

Schroeder has been sending samples from infected plants to researchers at the UI Parma Research and Extension Center as they seek to expand testing capabilities at their diagnostics laboratory to include SBWMV.

“I think our efforts are going to be to continue educating growers as we move into our field days this year,” Schroeder said.

SBWMV is vectored and transmitted by a soilborne fungus-like protozoan, Polymyxa graminis, which is a parasite of plant roots.

“Once it gets into the soil it can persist indefinitely on whatever plant happens to be in the field, and when you have a susceptible host like winter wheat, the virus is transmitted into the plant,” Schroeder said. “While crops other than winter wheat are not hosts for SBWMV, you can’t rotate crops to manage the disease.”

The best management practices for limiting the spread of SBWMV are sanitizing farm equipment and planting resistant winter wheat varieties.

In highly infected fields, it may be wise to plant a blend of resistant varieties and high-yielding, locally adapted varieties. Fumigation could be a management option, though it isn’t cost-effective in wheat production.

The list of SBWMV-resistant winter wheat varieties adapted to northern Idaho conditions is limited. University researchers may thoroughly evaluate germplasm for additional sources of resistance.

“We are just going to have to learn to live with a new virus like they have in Washington and Oregon,” Finkelnburg said. “They haven’t quit farming wheat because it showed up. They just farm a little differently.”