Pathogen(s) causing disease: Barley yellow dwarf virus, BYDV and Cereal yellow dwarf virus, CYDV
Symptoms: BYDV often occurs in patches that are 1 to 5 feet in diameter. Plants in the center of the patch are typically stunted, and plants on the edge of the patch are typically normal in height. The primary symptoms of the disease are stunting, and leaf tip yellowing, reddening, or purpling of leaf tips.
The color of the symptoms depends on the variety. In most cases, the discoloration of the leaf tips increases over time until eventually the entire leaf is discolored. Leaves affected with barley yellow dwarf often have small black spots or streaks spaced randomly over the discolored part of the leaf tip.
Conditions: Barley yellow dwarf is probably the most important and widespread virus disease of wheat and occurs worldwide wherever wheat is grown. The disease, initially thought to be caused by one virus, is caused by two or more related barley yellow dwarf viruses.
The barley yellow dwarf viruses have a wide host range among cereals and grasses, and severe losses occur in oats, barley, and wheat especially if infection is early. Depending on the virulence of the virus isolate in a given variety, infection may contribute to winter kill in regions with harsh winters, induce plant stunting, inhibit root growth, reduce or prevent heading, or increase plant susceptibility to opportunistic pathogens and other stresses.
Management: The primary control is to avoid early planting. Early planting allows maximum time for aphids to infect the plants in the fall. Plant after the Hessian fly-free date to minimize the risk of BYD infection.
No varieties have high resistance to BYD, but some are more tolerant than others. Under severe BYD pressure, a tolerant variety (rating 4 or 5) might have a loss around 15 per cent while a susceptible variety (rating 8 or 9) should have more than a 30 per cent loss.
A seed treatment systemic insecticide called Gaucho from Bayer CropScience is labeled for BYDV control. It has shown fair to good suppression of BYD in university trials. The variability in effectiveness is probably due to the timing of aphid infestation.
Sources:
Kansas State University http://www.ksre.ksu.edu/wheatpage/pests%26diseases.htm
Oklahoma State University http://entoplp.okstate.edu/classes/plp5013/wheattext.pdf
