The level of stripe rust in Pacific Northwest wheat fields this year mirrored earlier predictions of a normal year, said Xianming Chen, a USDA Agricultural Research Service research geneticist in Pullman, Wash.
Stripe rust was “quite normal” in commercial fields, but “very severe” in experimental fields, where Chen and researchers included some highly susceptible wheat varieties to better screen germplasm for resistance.
“A good year for farmers, and also a good year for us,” Chen said.
Chen recommends farmers plant only varieties resistant to stripe rust. On a scale of 1 to 9, with 1 being most resistant and 9 being highly susceptible, he urges farmers to plant a variety rated 1 to 4.
Growers must consider many traits in choosing a wheat variety, Chen said, including yield. But if it’s a choice between two equally high-yielding varieties and similar qualities, he advises selecting the one with better stripe rust resistance.
Seahawk, a soft white spring wheat from Washington State University, has the highest level of resistance to stripe rust, Chen said. But this year, one late-planted irrigated seed production field of Seahawk developed a problem with leaf rust, Chen said.
Stripe rust and leaf rust are different diseases caused by different species within the same fungal genus. Chen said stem rust has not been found this year on wheat or barley in the Pacific Northwest.
Mike Pumphrey, spring wheat breeder at WSU, said farmers who plant the variety in limited irrigated acres in southern Idaho, central Oregon and California should be aware of the situation, but he’s not worried about a larger outbreak.
“It’s not an alarming thing, it’s not necessarily surprising. It’s more of an unusual novelty that we had a field get leaf rust,” Pumphrey said.
Leaf rust is not a concern for dryland farmers, Pumphrey said.
His breeding program typically uses genes resistant to both rusts.
“Seahawk is kind of an exception, with having a couple seedling resistance genes for stripe rust,” Pumphrey said. “It has some adult plant resistance in the background, but maybe not enough.”
Pumphrey said he’s more concerned about head scab or fusarium head blight than leaf rust in irrigated fields.
This year, many farmers made one fungicide application at the time of herbicide application to address stripe rust. Second applications were not as widespread this year as in the past few years, Chen said. He’d like to increase the level of resistance to the point that fungicide applications aren’t necessary, even during a severe stripe rust year.
Chen said he’s heard from farmers who believe spraying fungicide on a resistant field without stripe rust will boost yields.
Generally, there’s not enough evidence to support that theory, he said, but he’s testing popular fungicides, noting he hasn’t studied all the chemicals in them.
“Our recommendation is always use fungicide when needed,” he said.
Stripe rust is never gone, but cannot currently be seen in most fields, except at high elevations, Chen said.
The outlook for stripe rust next year depends on the amount of precipitation in September and October, meaning potential fall infection and then whether cold conditions and snow cover in the winter help rust to develop.
Chen will monitor conditions and release predictions in early January and early March.