Stripe rust latest disease to hit Midwest wheat

posted Dec. 3, 2016 6:25 p.m. (CDT)
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MADISON — Yields of winter wheat in Wisconsin were good in 2016, but they could be even better in the future if farmers do a better job of managing for pests and selecting disease-resistant varieties.

Damon Smith, a UW-Madison assistant plant pathology professor, said while many wheat growers prepared to battle fusarium head blight in 2016, the amount of head blight was low, but the occurrence of a different disease, stripe rust, was relatively high.

As wheat acreage has increased in Wisconsin, the amount of stripe rust has increased with it, Smith said Nov. 29 at the Wisconsin Crop Improvement Association annual meeting.

“Stripe rust was a big problem this year,” Smith said. “We got hammered. We had the yield potential for 130 bushels per acre, but in some cases we lost 10, 15 or 20 bushels per acre because of stripe rust. We have to do something.”

Smith said UW-Madison researchers began doing field trials in 2015 to determine how to manage stripe rust, evaluating fungicide application timing on three winter wheat varieties and determining how well various varieties suppress the disease.

Stripe rust has become an increasing concern on Midwest winter wheat production since about 2000, Smith said. The disease can be identified readily by the bright yellow pustules that typically occur in a striped pattern on the surface of the leaf.

Because it is thought that stripe rust cannot overwinter in northern states such as Wisconsin, the pathogen most likely is windblown from the southern U.S., Smith said.

“That is why we need to pay close attention to stripe rust reports from the southern states,” Smith said. “I start watching reports even this time of the year. They already have rust on seeded wheat in the South. When we see it in southern Illinois, we start scouting here.”

Some states do spore trapping and monitor the disease via drones and airplanes, Smith said. Research networks across the country spread the news about what is found.

“Timing is everything” when it comes to stripe rust treatment, Smith said.

“The fungicide only lasts two to three weeks, so you have to time application to when the epidemic is coming in,” he said. “With warmer springs, stripe rust gets started earlier in the South so it comes up this way earlier. The earlier an epidemic starts in wheat, the more substantial its impact will be on yield.”

Some stripe rust-resistant wheat varieties do a good job of holding the disease at bay, Smith said. He urged growers to pay special attention to variety trials in winter wheat to try to balance head scab resistance with rust stripe resistance.

“Try to choose varieties that worked well over multiple years in multiple locations,” he said. “As margins on crops are narrower and narrower, we want to try to spray it if we can. If we do spray, we want to get the timing right. Getting (stripe rust) resistance in there would be helpful.”

Growers shouldn’t use a fungicide until they first see stripe rust in their fields. That will likely be at flag leaf emergence or the boot stage in Wisconsin.

Diversity important

Lucia Gutierrez, an assistant professor in the UW-Madison agronomy department, said researchers and seed marketers have to make sure to maintain diversity as modern wheat varieties are developed.

“We need diversity to maintain genetic gain,” Gutierrez said. “Disease resistance/​susceptibility is one of the reasons we need diversity.

Gutierrez used the example of the Irish potato famine in the 1840s, where disease wiped out an entire crop that didn’t have any genetic diversity. About 1 million people died and another 1 million left the country because of the famine.

At a smaller scale, corn leaf blight cost corn growers about $1 billion in the 1970s, Gutierrez said, again when there was a lack of crop diversity.

Breeding for durable disease resistance requires the evaluation of diverse genetic panels, she said.

“When you make a cross between a resistant and susceptible seed, it will help you select the seed that is better,” Gutierrez said.

“All of this needs to be taken into account in a breeding program to make sure we have enough diversity in the field, so we do not have problems as growers had with potatoes and corn in the past.”

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