Possible ‘Nightmare’: Moist, cool spring could mean repeat outbreak of stripe rust

A ladybug sits on a blade of rust-speckled wheat on Bill Myers’ farm near Diamond. -photo by Bill Myers

A cool, wet spring this year has created the perfect breeding ground for stripe rust, and WSU rust expert Xianming Chen is urging farmers to spray fungicide early to combat infestation.

“Winter wheat fields should be checked immediately if they have not been sprayed,” Chen wrote in a rust update Friday. "If active rust infection (producing rust powder) is observed quite commonly throughout the field, spray should be done as soon as possible.”

Chen advised farmers who have already sprayed their fields to keep an eye out for signs of rust as the season advances. They may need to make second or third applications to hold it off.

Steve Van Vleet, agricultural agent for WSU’s Whitman County extension, said he has seen a lot of orange streaks in fields across the Palouse.

Stripe rust fungus thrives in cool, wet temperatures. The combination of this damp spring and spores left in fields from last summer’s heavy rust infestation heightens the potential for another heavy infestation this year.

“It could be a nightmare,” said Van Vleet. “We originally thought it would be about 70 percent as bad as last year. Who knows, really, but I could see it being as bad, if not worse than last year.”

Chen warned cool and moist weather predicted for the next couple weeks will leave wet soil and cause morning dew, both said to be “very conducive” to rust development.

Many wheat breeds carry High Temperature Adult Plant genes that will kill off rust when plants receive higher temperatures.

Van Vleet said that resistance typically kicks in after a few consecutive days of temperatures above 65 to 70 degrees.

Fungicide applications from last year’s outbreak proved effective in many varieties of wheat, Chen reported last fall. Yields for Xerpha wheat were 95 bushels per acre when sprayed with fungicide. Without spray, Xerpha crops yielded 70 bushels per acre.

Fields of Madsen wheat yielded 110 bushels of wheat when not sprayed for rust. Spray made little difference on Madsen crops, adding just one bushel per acre to the yield.

In Spring varieties, Louise, the most commonly planted spring wheat in Washington last year, lost 8.5 bushels per acre to rust. Hank, on the other hand, yielded 44 bushels per acre when sprayed; 23 bushels per acre when not.