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A Sickly Harvest

By Emily Unglesbee
DTN Staff Reporter

ROCKVILLE, Md. (DTN) -- The winter wheat harvest will be a lot shorter than usual this year for Kent Eddy.

The western Kansas farmer estimates he will only harvest 60% of his wheat crop where he farms near the town of Syracuse.

The culprit?

Wheat streak mosaic virus (WSMV), which spread across the western third of Kansas this year, yellowing fields and decimating yield potential. While there's little that can be done about the 2017 damage, wheat disease experts say the situation this year could lead to even more problems in 2018.

"It is by far our biggest concern of the year," said Kansas State University wheat and forages production specialist Romulo Lollato. "Area abandonment of infected fields will be especially big this year."

Eddy destroyed 20% of his worst acres and planted sorghum. He estimates another 40% of his acres have some level of infection and will not yield well.

Several factors united in 2016 to cause the widespread outbreak of wheat streak mosaic this year, Lollato said. First, a wet summer allowed abundant volunteer wheat growth, which can house the wheat curl mite. The mite carries the virus.

The long, warm fall permitted mites to survive and spread through winter wheat extensively. At the same time, unusually high fall temperatures broke down the genetic resistance in varieties available to farmers.

THE VOLUNTEER PROBLEM

Volunteer wheat plants that survive into the fall can provide a home for the wheat curl mite until the new crop emerges. Usually, wheat farmers can get away with spraying volunteer wheat plants just once or twice each summer, Eddy noted. A herbicide pass in July controls the early post-harvest flush, and a second spray in August kills off any stragglers.

With plenty of moisture and a record large wheat crop coming out of the field, volunteer wheat plants came up continuously last summer, Lollato said.

"We heard of farmers that had to control it four times in the summer," he said. "It becomes really cost prohibitive," he added, noting how low wheat prices have fallen.

As a result, many missed the later flushes or simply didn't spray at all. The unusually warm fall weather helped the mites spread and hampered the effectiveness of the two WSM-resistant genes available in certain wheat varieties.

"When daily temperatures -- day and night -- are averaging above 65 to 70 degrees (Fahrenheit), then that genetic resistance is broken down," Lollato said. "Generally, we wouldn't see that break down until later in the spring."

ABANDONED FIELDS AND FALLING YIELDS

Wheat streak mosaic can cause a range of yield loss, with fall infections ranking as the most damaging.

Many fields this year will be completely lost to the disease, particularly in western Kansas, Lollato said. He recalled driving a 50-mile stretch in west-central Kansas without seeing a single healthy field this week.

The disease turns leaves yellow, often with faint green stripes from the veins, which give infected fields a pale, sickly appearance from the road.

"Every single field was completely overtaken by wheat streak mosaic," he said. "Most of those fields will be abandoned."

Eddy feels fortunate to have been able to replant 20% of his worst fields and recoup some of the losses. But another 40% of his winter wheat has varying levels of infection, which can drop yields dramatically.

Lollato recently viewed a yield map from one western Kansas producer from a field with severe wheat streak mosaic infection.

"Yields were ranging from zero to 35 bushels per acre, with the majority being below 10 or 15 bushels," he said. "Producers that will take many of these fields to harvest -- that is the level they will see probably."

LOOKING AHEAD

One Kansas State researcher, Bernd Friebe, has developed another source of genetic resistance to wheat streak mosaic. This gene, first found in wheatgrass, tolerates higher temperatures and should prove valuable to Great Plains growers, he told DTN.

However, any wheat lines with the new gene, Wsm3, are likely several years from commercialization.

For now, wheat growers must make volunteer wheat control a priority this summer if they want to avoid the same problem next year.

Lollato stresses that growers must think of their neighbors as well of themselves, given how easily the mite can blow from field to field in the fall.

"It's a community problem and we have to act as a community," he said. "If you see neighbors that have volunteer wheat, talk to them and have a conversation about it."

Fields hit by hailstorms during grainfill periods will be most at risk for heavy volunteer populations, he added. Hail damage at this stage can leave many viable seed heads on the ground, which will sprout later in the summer.

"So producers who had hail any time from May on will have a lot of volunteer wheat," Lollato warned.

For more information on controlling wheat curl mite and the viruses it carries, see this Kansas State article: http://bit.ly/….

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

Follow Emily Unglesbee on Twitter @Emily_Unglesbee

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