Wheat Vigilance

Time to Scout for Wheat Diseases in Fast-Maturing Crop

Emily Unglesbee
By  Emily Unglesbee , DTN Staff Reporter
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Stripe rust may have overwintered farther north than usual this year, thanks to a mild winter and plenty of inoculum in last year's wheat fields. Scout fields early and often. (Photo courtesy Tom Allen, Mississippi State University)

ROCKVILLE, Md. (DTN) -- Forecasts for a wet spring are music to the ears of Great Plains wheat growers, but beware -- the fungal diseases lurking in wheat fields are rejoicing as well.

"We are expecting above-normal precipitation for the spring and into summer, and because of the moisture -- which we are getting right now -- we are likely to have disease problems in wheat," warned University of Nebraska Extension plant pathologist Stephen Wegulo.

Growers should be scouting immediately for diseases like stripe rust, tan spot, Septoria leaf blotch and powdery mildew, all of which are favored by high moisture conditions.

The good news is that stripe rust infestations, which roared across the Great Plains in 2015 and 2016, are looking tamer in their breeding grounds in Texas and Oklahoma this spring. The bad news is that the mild winter experienced by much of the country this year has given the disease a good chance to survive farther north than usual, Wegulo told DTN.

We usually get cold enough temperatures in the winter to kill it," he said of Nebraska. "But when we have a mild winter, it can overwinter where there is a significant amount of snow cover."

STRIPE RUST

A number of growers in the panhandle of Nebraska saw stripe rust taking hold in winter wheat fields in the fall of 2016, Wegulo said. Those fields will be most at risk for overwintering fungi and early springtime infestations, he warned.

Other high-risk fields are wheat-on-wheat fields that are no-till or conservation tillage or anywhere wheat stubble has persisted. Wheat stubble gives stripe rust inoculum a good place to survive the winter, Wegulo said.

"For those growers, I would definitely scout at least once every couple weeks now, and then by the second half of April, they really want to be out there once a week to scout to see if stripe rust overwintered," he said.

Typically, stripe rust blows up into the Great Plains from infestations in Texas and Oklahoma, where the disease survives each winter. For now, those areas are not seeing significant problems with stripe rust, which is good news for northern wheat growers.

"Foliar wheat diseases remain relatively quiet in Oklahoma," Oklahoma State University Extension plant pathologist Bob Hunger announced in his university newsletter.

"Stripe rust in Texas was there early, but it has slowed down considerably, and by mid-March there wasn't any in Oklahoma and there had not been any reports of it in Kansas, either," Wegulo added.

Look for yellow pustules on wheat plants when scouting for stripe rust. The leaves are too young to display the characteristic stripes that the disease forms later in the season, Wegulo said. Pustules clustered low in the canopy will signal that the disease overwintered, he added.

"If stripe rust is detected, even if it's just a small hotspot, it would be wise to apply a preventative spray of a fungicide," Wegulo said. "Even those who sprayed early will still have to spray at flag leaf, unless the weather dries up completely," he added.

That's a tough prescription for farmers facing low wheat prices, so Wegulo recommends they consider generic products and keep in mind that the fungicides that control stripe rust will also control a host of other wheat diseases at play this spring, such as fungal leaf spot diseases and powdery mildew.

FUNGAL LEAF SPOT DISEASES

Fungal leaf spot diseases such as tan spot and Septoria leaf blotch easily overwinter in the Great Plains by hunkering down in tough fruiting structures that can withstand very cold temperatures.

That means these diseases are alive and well in any wheat stubble of previously infected fields. Like stripe rust, they do well in wet and cool conditions and should be scouted for immediately, particularly if growers faced infestations last year, Wegulo said.

At this point in the season, tan spot and Septoria leaf blotch are mostly indistinguishable and will manifest as dark brown spots with a yellow halo on the lower leaves of the plant.

POWDERY MILDEW

Another wintry lurker is powdery mildew, which survives on wheat stubble and favors high humidity, such as you might find in dense lower canopies of a wheat field.

Look for powdery white fungal growths on the surface of wheat leaves and stems, Wegulo said. "When conditions are favorable, it will move up the plant and you will see it on upper leaves," he added. "But early in the season up to first week of May, you will mostly see it in the lower canopy."

For more information on identifying and treating these diseases, see Wegulo's university news release here: http://bit.ly/…

Find UNL's scouting guide here: http://bit.ly/…

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

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(PS/AG)

Emily Unglesbee