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University of Idaho Extension cereals pathologist Juliet Marshall shows a sample of winter wheat brought in by a grower with symptoms of barley yellow dwarf virus. Marshall said the sample, found near American Falls, didn't have an insecticidal seed treatment, which is a recommendation for limiting damage, and she anticipates widespread infections this season.

Capital Press

ABERDEEN, Idaho — Based on the volume and distribution of recent grower reports about barley yellow dwarf infections in winter wheat, University of Idaho Extension cereals pathologist Juliet Marshall said it’s clear the disease will be rampant again this season.

Last season, Southern and Eastern Idaho grain growers coped with the most widespread barley yellow dwarf outbreak they’d ever experienced. The virus is spread by aphids, causes yellowing of leaves and stunts plant roots.

Though an abnormally wet May helped plants grow out of their symptoms in 2015, many growers still experienced yield losses of up to 40 percent, Marshall said. Marshall fears the disease is at least as widespread as last year, and absent another break from Mother Nature, yield losses could be greater.

Coupled with slumping commodity prices, Marshall worries Idaho wheat and barley returns could suffer.

“It’s going to be widespread again,” Marshall said. “There are some growers who feel like it’s going to be worse, but at this point, we can’t tell.”

Marshall said growers have brought half a dozen samples of infected plants to her office, and she’s been flooded with calls, confirming the disease is present in fields from the Idaho and Utah border, north to Blackfoot and west to Twin Falls County. Even before the first snow of winter fell, Marshall said barley yellow dwarf cases were confirmed in fall wheat fields near Seagull Bay of the American Falls Reservoir, Fort Hall and in the Arbon and Rockland valleys. She said growers have found infected plants throughout fields, often with the heaviest infections occurring along field edges.

“Barley yellow dwarf is going to be pretty visible here in the next several weeks,” Marshall said.

Marshall believes barley yellow dwarf has been present in the region for a long time but said it first became a noticeable problem in 2008. She believes infection rates have risen as the state’s corn acreage has increased. Corn supports aphids until fall grains sprout and lure them away.

Marshall advises farmers to use insecticidal seed treatments and delay planting fall grain as long as possible to reduce exposure to aphids before cold weather keeps them in check. Marshall said most of the reported infections were from early planted grain, but she acknowledges some growers wouldn’t have enough time to plant if they delayed.

This spring, she advises growers to control volunteers to eliminate potential sources of virus and aphids, and to plant spring grain as early as possible, allowing the plants to mature and be hardy when aphids arrive.

Marshall said UI has no good recommendations on resistant varieties but has been evaluating some potentially resistant Kansas State University varieties in research plots in Buhl, where UI is also evaluating the efficacy of insecticidal seed treatments and additional foliar sprays in the fall. She also advises growers to keep crops well watered and fertilized, as the virus robs plants of nutrients and moisture to replicate itself.

UI agronomist Xi Liang is leading greenhouse and field studies to evaluate how adding different levels of supplemental nitrogen in the spring may curb yield losses. She’s also evaluating how sick plants absorb moisture.

“We’ll collect roots at the end of the study to see if the roots are affected by barley yellow dwarf virus and damage (water) uptake from the soil profile,” Liang said.

UI barley agronomist Chris Rogers is overseeing similar trials in barley, and plans to evaluate a new European variety, Wintmalt, for yellow dwarf tolerance.

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