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Winter Wheat Shows Signs of Foliar Diseases

Rust pathogens – even mites – are showing up this fall.

Crop scouts are noting an assortment of challenges facing winter wheat growers this fall. From mites to viruses, there is enough activity that farmers should be out scouting fields.

Pathologists in the High Plains are noting cases of leaf rust and stripe rust in wheat fields from Stillwater, Oklahoma, to near Red Cloud, Nebraska.

Although much of the winter wheat-growing region has been drier than normal, areas where sufficient rain (or even dews) have occurred – combined with warmer-than-usual temperatures – are showing signs of these rust strains, says Bob Hunger, Extension plant pathologist at Oklahoma State University.

Hunger says growers should be wary of the diseases but should hold off on treatment. “I am not a proponent of spraying in the fall to control fall foliar diseases such as leaf rust because leaf rust development slows and stops once we get to winter temperatures, or less than 60˚F.,” he says.

University of Nebraska pathologist Stephen Wegulo notes that stripe rust has been present in western Nebraska wheat fields each of the last four falls, and it has been growing in severity each year. This is the first time it has been noted with widespread severity in eastern Nebraska and the first time stem rust is present throughout the state in fall-planted wheat.

In most cases, older and lower leaves with leaf rust pustules die, but younger leaves will be healthy and green. Folks who graze wheat fields will find that cattle eat up injured leaves (the infections are not harmful to cattle), and the grazing opens up the crop canopy, promoting air circulation that thwarts leaf rust.

Still, keep a watch throughout the winter. Oklahoma State’s Hunger points out that if a mild, damp winter occurs, the rust will survive and inoculum will be present in the spring. Growers should also watch for the presence of spotty leaf diseases such as tan spot and septoria leaf blotch, which usually do not appear until spring.

“Watch these fields starting in late February to see if an application is merited, because control of foliar diseases is much more critical in the spring than in the fall,” Hunger says.

Watch for Winter Mites

If foliar diseases aren't enough, growers also need to be on the lookout for winter mites, reports Kim Kohls, crops agent at Kansas State University’s River Valley Extension office in north-central Kansas.

Kohls found the tiny mites in a field in north-central Kansas. The dark blue insects have bright red-orange legs. They thrive in cool, moist weather and are most often found in loose, sandy, or loamy soils. They feed on plants mostly at night, puncturing leaf tissue and causing the leaves to turn silver-gray. Young plants are most susceptible and may become stunted. Control may be necessary if large portions of a field show symptoms, according to KSU. However, contact your crop protection dealer for control recommendations, as there is a limited number of products labeled for winter mites.  

Colder nighttime temperatures should help thwart the winter mites, Kohls says.

 

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