Wheat Disease Update

ROCKVILLE, Md. (DTN) -- Stripe rust is beginning to drift into the Great Plains and Midwest, after a long journey from its breeding grounds along the Gulf of Mexico.

The disease got a slower start this year, thanks to a cold winter for most of the U.S., plant pathologists told DTN.

Now its signature rusty orange spores have shown up as far north as southeastern Kansas and southern Illinois. Growers with susceptible wheat varieties should be on alert, especially if their forecast shows moderate temperatures and plenty of moisture, which allow the disease to thrive.

WHEN AND WHERE

Since early April, the disease has slowly crept into wheat fields in Arkansas, Kansas, Kentucky, Oklahoma and Tennessee.

But infestations were light and sporadic, in part thanks to unfavorably dry conditions in the Southern Plains and a delayed crop, noted Kansas State University plant pathologist Doug Jardine.

Now the disease may be picking up steam. Oklahoma State University Extension Wheat Pathologist Bob Hunger has reported more severe infestations in southern and central Oklahoma. "This activity will increase through the coming weeks as the forecast indicates continued moisture (rains and dew) coupled with moderate temperature," he told growers in his weekly Wheat Disease Update.

In southern Oklahoma, much of the wheat is heading into the flowering stage, which puts it beyond the application deadline for many wheat fungicides, Hunger noted.

But most growers in Kansas are still in the jointing stage of wheat, which leaves plenty of time to scout and protect the flag leaf, Jardine noted.

WHAT TO DO

Check your varieties' stripe rust ratings, said Nathan Kleczewski, University of Illinois plant pathologist. "Weather will play a big role but variety is a key factor in whether or not disease is going to develop," he said.

If you have a susceptible variety, or there is no rating for stripe rust, you need to scout.

"You don't want it to sneak up on you," Kleczewski said, as the spores can spread quickly when conditions are right. Look for streaks of rusty orange pustules on the leaves. If an infestation is plentiful, the spores will brush off the plant and coat your clothes and shoes with orange dust.

The disease is often confused with another wheat disease called leaf rust. Leaf rust pustules are usually darker and scattered randomly on the leaf, rather than in stripe formations. See a University of Nebraska guide on distinguishing the two here: http://extensionpublications.unl.edu/….

There is no simple spraying threshold for stripe rust. If you have a susceptible variety and decent yield potential in your field, with a favorable forecast and disease present in your field, a fungicide application is probably warranted, Kleczewski said.

That decision may be more fraught this year for Southern Plains growers facing drought conditions and freeze damage in their fields, Jardine noted. "A lot of yield potential is still to be determined, but we are not going to have any great yields in Kansas this year," Jardine said.

"Years and years of data show that, in a normal year, you can see a 10% yield bump from putting a fungicide out," he added. "I think if you've got pretty susceptible variety and you think you can get 30 bushels [per acre], then I would go ahead and use a $2 [per acre] generic fungicide."

See this Kansas State publication for guidance on fungicide efficacy on stripe rust: https://www.bookstore.ksre.k-state.edu/….

For more details on how the Great Plains wheat crop is faring, follow DTN's reporting on the Wheat Quality Council's Winter Wheat Tour this week, starting here: https://www.dtnpf.com/….

You can reach Emily Unglesbee at Emily.unglesbee@dtn.com

Follow her on Twitter @Emily_Unglesbee

(PS/AG)

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