Barley yellow dwarf symptoms and control
Barely yellow dwarf had been reported in multiple regions of Kansas this spring. Reick DeWolf, Kansas State Extension was in many fields in Marion County with significant yellowing from what he suspects is barley yellow dwarf. Other fields in central and south central Kansas also appear to have low levels of the disease. Historically, barley yellow dwarf is most common in eastern and central Kansas. It can occur anywhere in Kansas, however.
The primary symptoms of barley yellow dwarf are stunting and yellow or red discoloration of the leaf tips. The disease can be uniformly distributed in fields, but it is most commonly found in patches that are 1 to 5 feet in diameter. Stunting is typically most severe near the center of a patch. 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. The midrib of the leaf often remains green longer than the edges of the leaf.
Typically, there is no mosaic pattern on the leaf, but sometimes there is some striping at the border between the discolored leaf tip and the green leaf base. In addition, leaves affected with barley yellow dwarf often have small black spots or streaks randomly spaced over the discolored portion of the leaf tip. These are presumably opportunistic infections by bacteria.
Barley yellow dwarf often occurs in 1- to 5-foot diameter patches. Infection by barley yellow dwarf is often associated with the occurrence of dark heads with shriveled grain. These occur in small patches similar to barley yellow dwarf patches. It has not been conclusively proven, but it is suspected that barley yellow dwarf causes the dark heads.
Barley yellow dwarf can be confused with other production problems such as wheat streak mosaic or nutrient deficiency. Accurate serological tests for barley yellow dwarf virus are available from the Plant Diagnostic Lab at Kansas State University.
The amount of yield loss depends on the percentage of plants showing symptoms. Casual observation often overestimates the percentage of infected plants. Collecting random samples while moving through a field in a systematic way will give a more accurate estimate of the incidence of infected plants.
The timing of the infection relative to crop development also influences the potential yield loss associated with barley yellow dwarf. When infection takes place in the fall, the virus has more time to disrupt plant growth and losses can exceed 35 percent. If plants are infected after heading; however, the risk of severe yield loss is reduced.