Stripe rust levels are so low Eastern Washington farmers are being told not to spray fungicide unless they see the disease in their fields, researcher Xianming Chen says.

“Later on, rust definitely will show up,” said Chen, plant research geneticist for USDA’s Agricultural Research Service in Pullman, Wash. “This year, we probably need to pay more attention to the flag leaf stage to see if rust shows up in individual fields.”

Chen and his team of researchers did not see stripe rust in commercial fields in Central Ferry and Walla Walla, Wash., and Hermiston, Ore.

At USDA’s conservation farm near Pullman, researchers had to inoculate the wheat to ensure they have good data to screen germplasm for resistance.

Chen attributes the low levels to a cold winter, particularly the “unusually cold” weather the week between Christmas and New Year’s Day.

The current pattern is similar to last year, Chen said. He expects rust to begin showing up in late May and early June.

“We still need to keep our eye on the fields,” he said.

During the next few weeks, the temperature will be right for the fungus, Chen said. The most favorable weather for stripe rust is frequent rain.

Chen recommends against the winter wheat varieties UI Magic and WB4303 and spring wheat varieties WB6341 and WB1035 CL+, which are particularly susceptible to the fungus.

Farmers who have planted those varieties should check their fields and apply fungicide, he said.

“Hopefully, varieties like UI Magic will eventually disappear,” he said.

Chen will issue his next report later this month.