Wheat Gets Rusty

3 Jun 2016

By Emily Unglesbee
DTN Staff Reporter

ROCKVILLE, Md. (DTN) -- Winter wheat stages across the U.S. range from full maturity to flowering, but one consistent theme this spring is the disease called stripe rust.

The yellow-orange pustules have swept through fields from Oklahoma and Kansas up into the Dakotas and east into the Great Lake states.

"The weather conditions were just right for stripe rust this year," noted Oklahoma State University Extension plant pathologist Bob Hunger. "It started early down in southern Texas, and the winds blew it north, where it was favored by the cool, wet conditions that we had through a fair amount of the spring."

Wheat harvest is beginning to get underway in southern Oklahoma, so the rust's reign is over there, but the disease is hitting its stride in the maturing wheat crop of Nebraska, the Dakotas, the Great Lake states, and Ohio.

"This is the most widespread and the earliest I have seen this disease in the state in 13 years," Ohio State University plant pathologist Pierce Paul reported in a disease round-up from Oklahoma State.

Flag leaves are fully emerged and some fields are starting to head in Leon Kriesel's fields near Gurley, Nebraska. Every field has some disease in it, he told DTN in an email. "I have not seen any variety that has not been infected by the rust," he reported. "The rust keeps changing races so some [varieties] that were okay before may not be now."

CHIPPING AWAY AT A BIG CROP AND SMALL MARGINS

The cool wet conditions that have favored stripe rust have also given most wheat producers one of the best crops they've seen in years. "We've got such good moisture now," University of Nebraska cropping systems specialist Bob Klein told DTN. "But that means disease is a main concern, too."

With wheat prices hovering under $5 per bushel, producers face the unpleasant task of spending extra to protect a low-value crop, Hunger noted.

Oklahoma yields are unlikely to drop too much as a result of stripe rust, mostly because producers went ahead made timely fungicide applications. "The only alternative was harvesting a crop with poor test weight and bad yield," he said.

In Kansas, most growers were also proactive about spraying, so Kansas State University wheat and forages specialist Romulo Lollato is optimistic that the yield potential remains very good.

Growers with susceptible varieties who opted not to apply fungicides are likely to see 30% to 40% yield loss or more, however, he said.

Kriesel said the decision to spend at least $10 an acre to spray fungicides was easy for his operation, where they grow wheat for seed. A few others chose not to. "Some fields in the area are on the verge of being gone," he said. "[They] will not make it to harvest, they look like you sprayed them with Roundup.

"Yields will be very poor in the higher infected fields and test weights will be low," Kriesel said of his region. "The sprayed fields may still have some yield loss 1% to 5%, but test weights will be better."

To add insult to injury, many growers are also facing looming spray decisions for Fusarium head scab, South Dakota Extension plant pathologist Emmanuel Byamukama noted in the Oklahoma State disease round-up: "The challenge is going to be needing another fungicide shortly for scab management. And with the wheat prices not encouraging, producers are concerned applying 2-3 fungicides in winter wheat this season."

WATCHING THE WEATHER

The rest of June's weather will be key, not just for the spread of stripe rust, but also for the wheat headed toward harvest in Oklahoma and Kansas. Hunger said producers in the farthest southern reaches of Oklahoma are just starting to harvest, and Lollato estimated that harvest in southern Kansas will probably get underway in a week.

Wet weather has already kept mature wheat sitting past its ideal harvest date in the southern Oklahoma, Hunger said. Sprouting and falling test weights will be a concern if fields don't dry out soon.

In Nebraska, producers are hoping for drier weather and higher temperatures, which could slow the spread of stripe rust, Kriesel said.

"Overall, I would say with warm and dry weather for the next 2-3 weeks, yields will be down 10% to 20% in the area, and with wet, cool weather, it is going to be ugly -- down 40% to 60%," he said.

Lollato urged Kansas producers to keep an eye out for head scab, which is already starting to show up in north and south-central regions of the state. Wheat streak mosaic (WSM) has also surfaced in several states this year, and Lollato urged growers to kill any volunteer wheat this summer. Wheat curl mites, which vector WSM, use volunteer plants to survive and lay eggs, he explained.

For more information on stripe rust, see this Kansas State University publication: http://bit.ly/….

You can find Oklahoma State's disease round-up here: http://bit.ly/….

Emily Unglesbee can be reached at emily.unglesbee@dtn.com

Follow Emily Unglesbee on Twitter @Emily_Unglesbee.

(Ps/CZ)