U of I cereals pathologist concerned about Idaho stripe rust outlook

A University of Idaho cereals pathologist is advising the state’s grain farmers that conditions appear optimal for pressure from a fungal disease that can devastate crop yields, known as stripe rust.

Initial symptoms of stripe rust include small chlorotic lesions on leaves, followed by the emergence of light-orange pustules from these lesions, each containing thousands of spores. Pustules develop parallel to leaf veins forming stripes.

Professor Juliet Marshall, associate director of the Idaho Agricultural Experiment Station, offered an outlook for stripe rust and other diseases affecting wheat and barley during the East Idaho Cereals Conference, which University of Idaho Extension hosted Feb. 5 at the Shoshone-Bannock Hotel and Event Center in Fort Hall.

Marshall explained prevailing winds can carry stripe rust spores originating in northern California into southern and eastern Idaho. Extremely wet recent weather in northern California portends trouble with late-season stripe rust infections for Idaho grain growers from the Magic Valley through north of Idaho Falls.

“When northern California has plenty of moisture then they usually have good growth of cereals down there, and that means the stripe rust is going to be a problem,” Marshall said.

Stripe rust surfaced in wheat and barley fields throughout southern and eastern Idaho beginning in early June last season. On high-elevation dryland farms, Marshall worries fall-planted wheat that’s insulated throughout winter by snow cover could carry stripe rust spores into the spring, causing much earlier and more serious infestations.

“I think there was some significant inoculum that could potentially have infected some of our fall grain. If that is the case and we have early season infections we will have significant impact from stripe rust next spring,” Marshall said. “For dryland producers in upper-elevation areas, wheat should still be under snow and could potentially be protecting stripe rust. They need to be scouting early in spring when wheat plants are greening up.”

Most irrigated farms are located at lower elevations, where Marshall believes the weather has been warm enough this season to melt the snow cover, exposing stripe rust spores to hard freezes, which should kill any inoculum.

Growers can effectively protect themselves from stripe rust by applying fungicides or planting resistant wheat or barley varieties.

A few high-yielding wheat varieties that are commonly raised in the region — including the hard white spring wheat UI Gold, the hard white spring wheat WB7696 and the hard red spring wheat WB9707 — performed worse than expected against stripe rust last season. Options that continue to exhibit strong resistance include Dayn, Hale, WB9668, WB9636, WB9623, Seahawk and Ryan, among others.

“A lot of people weren’t spraying fungicides because stripe rust came in so late and it significantly affected the yield of some varieties,” Marshall said, adding that one field planted with a susceptible hard white spring wheat sustained yield losses of more than 50%.

Marshall encourages farmers to report stripe rust immediately upon spotting it to help warn other area farmers. UI Extension manages a pest alert website that provides farmers with advanced warning when diseases such as stripe rust are poised to move into their area. The site, https://pnwpestalert.net/, also offers management guidance.

“Stripe rust is a community and a communicable disease,” Marshall said. “It’s a community disease because if your neighbor has it, it’s likely to spread very quickly into your production.”

Northern Idaho farmers also appear to be in store for a challenging year with stripe rust, according to a 2025 stripe rust forecast recently issued by Xianming Chen, a research plant pathologist with the U.S. Department of Agriculture Agricultural Research Service in Pullman, Washington.

Chen is predicting potentially severe stripe rust infections in northern Idaho during the upcoming season, with yield losses of up to 57% possible. Chen wrote that warm weather last November and December has been conducive to stripe rust survival. Chen advises farmers who plant winter wheat varieties ranging from susceptible to moderately susceptible to stripe rust should consider an early fungicide application at the time of herbicide application.