By JOHN O'CONNELL
A crop disease spread by aphids, called barley yellow dwarf virus, is widespread in Magic Valley fall-planted wheat and barley fields ranging from Buhl to Murtaugh, University of Idaho Extension cereals pathologist Juliet Marshall says.
In an alert sent to update growers about various pests, Marshall indicated yield losses increase with earlier infections and can approach 100 percent in the most extreme situations, particularly in barley.
Marshall emphasized the virus is not seed-borne and can be spread only through movement of the aphid vector. She said transmission rates increase at lower temperatures.
Symptoms of the disease include yellowing of leaves, stunting of plants and roots, irregular and small heads and emerging leaves with scorched tips, twisting and abnormal development.
Marshall said infection occurred last fall when large populations of aphids, which grew during a mild fall with no hard frost until well into December, migrated from other crops to emerging wheat and barley. She said aphids are lured to lush fields under irrigation and frequently leave dryland field corners alone.
Marshall said aphid populations are now low, and spring grain crops should escape early barley yellow dwarf virus infection.
"At this point, reducing crop stress will reduce the effect of the virus on the plant but yield losses will occur both through reduced grain production, as well as reduced test weight," Marshall wrote in the pest alert. "The most effective control is through the use of resistant varieties, but insecticidal seed treatments may reduce the initial spread in fall wheat and barley."