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Stripe Rust Concerns Mount in Winter Wheat

Wait until flag leaf to treat winter wheat for stripe rust.

Early onset of stripe rust in wheat fields should have wheat producers cautious, but not yet seeking treatment, according to Erick DeWolf, plant pathologist at Kansas State University. The reports of stripe rust in fields in Oklahoma, Kansas, and Colorado this week are not yet widespread, but they are giving producers cause for concern. DeWolf doesn't advise treatment for the disease until after wheat is in the flag leaf stage. But it is a good time to do three things: scout fields, research which fungicide products you may wish to use, and determine whether a fungicide treatment will pay.

"Early onset of stripe rust almost always results in greater chance of yield loss," DeWolf says. "What we don't know is whether it will continue to spread."

Stripe rust thrives in cool and damp conditions, which have not been prevalent in winter wheat country yet this spring. If conditions turn cool and damp - like they did in 2015 - stripe rust could spread. Incidentally, those are also the conditions that maximize winter wheat yield.

Damp, cool weather over the weekend in much of Oklahoma and Kansas perpetuated stripe rust infestations, according to Bob Hunger, plant pathologist at Oklahoma State University. In his weekly wheat disease report, Hunger says that near Stillwater, Oklahoma, varying degrees of stripe rust were found. "In Kingfisher County I found scattered but not severe stripe rust. However, my impression is that stripe rust has the potential to increase dramatically if weather brings us some rains," he notes.

This past week was dry and windy across Oklahoma, so spores were spread, yet there was no moisture (dew or rains) to promote additional infection. The rain is certainly needed for the wheat, but it will also provide a favorable environment for stripe rust to increase because the temperature is supposed to stay in the 60s to 70s during the day and 40s to 50s at night, Hunger says. If warm and dry conditions persist, however, chances are the stripe rust infestations will be minimal. "Anything that causes you to question wheat yield potential, whether it is heat, drought, or freeze, all cause me to question whether to invest in protecting the wheat crop," adds DeWolf.

Lots of decisions need to be made

Stripe rust is hitting the winter wheat crop at a time when growers are also concerned about freeze damage and drought. That makes decision-making for stripe rust difficult, DeWolf says.

"The way I look at it is, we need to manage our wheat for maximum profitability. With the lower price of wheat, farmers should evaluate wheat fungicide options and prices, and monitor the severity of the disease threat," he explains. If the threat of stripe rust is low, save money and don't apply fungicide. But if the threat of stripe rust is high, yield loss from stripe rust could be as high as 30% to 40%, which warrants a fungicide application.

According to KSU research, a fungicide application prior to jointing doesn't pay. "An application between boot stage and flowering is most effective," DeWolf says. Growers can apply a fungicide earlier, but that may limit product options later in the season when a second application is necessary to protect the upper leaves. Right now, the plant pathologist recommends growers hold off on an early fungicide application to "get as much information as they can to make a good decision in what looks like a challenging wheat production year," he says.

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