Published 10:23 am Thursday, May 22, 2025
The wheat fungus stripe rust, previously found only in research fields so far this season, has now been found on farmers’ commercial fields in Washington, regional stripe rust expert Xianming Chen said in his latest update.
“That is not a surprise,” Chen told the Capital Press. He is a research plant pathologist for the USDA Agricultural Research Service in Pullman, Wash.
Following his May 7 update, Chen received a report of stripe rust in several Franklin County fields, where the winter wheat varieties Piranha CL+ and Nova AX were planted. Chen checked the fields May 9 and “stripe rust was easy to find.”
The same fields also had stripe rust last year, he said.
“Compared to last year, this year the rust was much later, and also light, and also low,” Chen said.
Chen also checked more than 10 commercial fields in Franklin and Adams counties. They found three additional fields with stripe rust, but the incidences were much lower than the first two fields.
Chen recommends farmers apply fungicide to winter wheat fields where susceptible and moderately susceptible varieties are planted, before flowering. If they applied fungicide more than three weeks ago, farmers should check their fields for active rust.
Spring wheat farmers should consider applying a fungicide at the same time of herbicide application, Chen recommends.
Stripe rust has been reported in Washington, Oregon, California, Louisiana, Texas, Georgia, Oklahoma and Texas. Stripe rust has appeared at relatively low levels compared to last year, except California,
“However, stripe rust may still have time and conditions to develop to epidemic levels in some regions,” Chen said in his update.
Recent cool temperatures and frequent rain showers were “extremely conducive” to stripe rust, Chen said in his update.
The low temperatures did not allow the varieties’ high-temperature adult-plant (HTAP) resistance to be fully effective. So varieties with moderate levels of HTAP resistance without any effective all-stage resistance, such as Piranha CL+ and Nova AX have been susceptible.
For HTAP resistance to kick in, temperatures need to be above 50 degrees Fahrenheit at night and above 70 degrees Fahrenheit in the daytime.
“The weather conditions forecast for the next two weeks will be continually favorable to the disease,” Chen said.
About 20% of wheat varieties are susceptible to stripe rust, Chen said. The number of susceptible acres planted for this year is not yet known.
Last year, Piranha was the most-planted wheat variety at 393,000 acres, about 20% of total soft white winter wheat acres and more than 15% total winter wheat acres. It ranks as a moderately resistant variety.
Piranha fared better in Pullman-area trials, where its yield loss was very low and stripe rust developed later and slower, than in locations where the rust started early and temperatures were low, Chen said.
The next three most popular varieties — LCS Shine, VI Voodoo and Norwest Tandem – have “very good resistance,” Chen said.
Very few of the breeding lines currently under development are very susceptible to the disease, Chen said.
“That’s good news — that means more new varieties have good resistance,” Chen said.
