Resistant wheat key to keeping stripe rust at bay

Look for spores | Producers told to be vigilant in scouting fields because ‘it can be like a steamroller once it gets going’

The photograph shown on a screen in the cavernous meeting room depicted a flat green open field. On the horizon was an orangey grey cloud.

Those who saw the cloud arrive in 2011 may not have realized the deadly potential it held for southern Alberta cereal crops.

It contained stripe rust spores originating in the U.S. Pacific Northwest that were blown to Alberta on the wind.

Stripe rust found ideal conditions and susceptible hosts in the region last summer, damaging winter wheat and spring wheat, with barley and triticale affected to a lesser extent.

Crop experts are now working to ensure 2012 doesn’t bring a repeat of cereal losses due to stripe rust. Some infection is likely, given prevailing winds, but producers can take preventive measures to limit stripe rust spread and damage.

Stripe rust works by invading the plant system, reducing photosynthesis and preventing kernels from filling.

“It basically hijacks the plant’s energy production system,” said Mike Harding, a plant pathology technologist with Alberta Agriculture.

He told the Irrigated Crops Production Update in Lethbridge Jan. 31 that planting resistant wheat varieties is the most important action this spring. The varieties come in two types: all-stage resistance and adult plant resistance.

The former provide immunity at all stages of plant growth, but their resistance relies on a single gene and may be rapidly overcome by stripe rust as it adapts.

Adult plant resistance, as the name suggests, manifests itself in older plants. Some are race specific, so growers need to do some homework before selecting a variety, he said.

Other steps include good crop rotation and avoiding “green bridges,” which are plant materials, weeds and volunteers that host the fungus and allow it to overwinter.

Harding advised farmers to scout crops and do it early.

“When the pustules first break open and you can still see those spores, it’s very easy to tell when you have stripe rust,” he said.

“As the disease progresses and the spores fall off or get blown away, it’s difficult to distinguish this from other things, like even cereal leaf beetle.”

A foliar fungicide application may be necessary if spores are found.

“If you’re in southern Alberta in an area where stripe rust has been found and you’re growing a susceptible variety, you’re in a high risk (area) and probably need to spray.”

Stripe rust thrives in cool temperatures and high moisture, which explains its increase in the last two years of good snow cover followed by cool wet springs.

It also makes it more of a problem in irrigated crops, where there is always good moisture.

“This is a cool season disease,” Harding said. “It prefers cooler temperatures and it can survive at -5 C. And it can actually grow, germinate and infect between 0 and 20 C, with the optimal being between 5 and 15.”

A cool spring favours early disease development, Harding said. Yield reductions of up to 75 percent aren’t unheard of in severe outbreaks.

“It’s definitely a disease that we take very seriously because it can be like a steamroller once it gets going. If a person wasn’t actively scouting for this disease, it can really catch you off guard.”

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