PULLMAN, Wash. — Scientists have reported the worst outbreak of stripe rust in recent years in Northwest wheat fields and it is being found much earlier in the season than usual.
Xianming Chen, USDA plant pathologist at Washington State University, says stripe rust is developing on susceptible winter wheat varieties in southeastern Washington and northeastern Oregon.
Diana Roberts, WSU area extension agronomist, Spokane, urged farmers to check their fields and determine whether infestation levels are high enough to warrant spraying with fungicides.
Chen recently found the stripe rust fungus in Franklin County fields seeded to Hatton variety. In several fields near Connell, more than 80 per cent of wheat plants in the entire field had stripe rust. Infestation levels ranged from 15 percent to 30 percent.
However, up to 100 percent of plants were infected in hot spots up to several hundred feet in diameter. In some places, the ground was covered with rust. Chen said he has received reports of stripe rust found on early- planted spring wheat varieties near Pendleton, Ore.
“Such a high level of stripe rust infection in eastern Washington at this time of year has not been seen for many years,” Chen said. “Heavy rust innoculum is already in the region and the weather has been very favorable to the disease and will continue being favorable for the fungus over the next 10 days. We expect stripe rust to spread and develop in eastern Washington.”
The stripe rust fungus flourishes when the weather provides frequent rain, wind and cool temperatures.
The disease shows up as orange pimple-like pustules arranged in fine lines or stripes along wheat leaf veins when plants have grown old. However, on seedling leaves, rust pustules are random.
WSU scientists caution against being too quick to spray. They say farmers should carefully identify the rust and determine whether the infestation level warrants spraying.
WSU scientists recommend growers consider spraying fungicide if the rust is found on 10 percent of any leaf on 10 percent of the plants in a stand. They also should consider whether the weather during the next few days will be wet or dry, cool or warm.
A heavy infection on a leaf will impede photosynthesis and grain fill. Yields in infected fields could be reduced by 30 percent to 60 percent. Stripe rust also reduces grain quality by lowering test weight.
Farmers who have questions about stripe rust should contact their local WSU Cooperative Extension Office, or Diana Roberts at (509) 477- 2167, e-mail robertsd@wsu.edu, or Xianming Chen at (509) 335-8086, Fax (509) 335-9581, e-mail xianming@mail.wsu.edu.
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