Barley yellow dwarf symptoms and control
By the time symptoms are visible, there is no way to control barley yellow dwarf. Plants showing symptoms were likely infected weeks or months ago. Producers should start planning a control strategy before planting.
The control of barley yellow dwarf is closely linked to control of the aphids that introduce the virus into the plants. One of the primary means of controlling barley yellow dwarf is to avoid early planting, which often increases the likelihood that aphids will infest a field in the fall. Planting after the Hessian fly-free date reduces the risk of aphid infestation and minimizes the risk of barley yellow dwarf infection. The Hessian fly-free date works well against barley yellow dwarf unless there is a mild fall that allows aphids to survive longer than usual. The aphids that survive these mild conditions can spread the disease and increase the potential for severe yield losses.
Ratings of wheat varieties can be found in Wheat Variety Disease and Insect Ratings, MF-991. No wheat varieties have high levels of resistance to barley yellow dwarf, but some are more tolerant than others. Under severe barley yellow dwarf pressure, a moderately resistant variety (rating 4 or 5) might have a loss around 15 percent while a susceptible variety (rating 8 or 9) could have more than a 30 percent loss.
Chemical control of the aphid vectors can suppress barley yellow dwarf. Unfortunately, spraying insecticides for aphid control has not proved practical. First, multiple applications would be required to achieve satisfactory control. Second, it is not possible to wait for obvious aphid populations before spraying because by the time they are detected, significant virus transmission would already have occurred. Therefore, applications would have to be made on a preventive schedule. Given the unpredictable nature of aphids and barley yellow dwarf epidemics, it is not economical to make several preventive sprays in the fall and early spring.
Seed treatments containing the systemic insecticides (e.g., Gaucho XT, CruiserMaxx Cereals) are labeled for aphid control. These products have shown fair to good suppression of barley yellow dwarf in university trials. The variability in effectiveness is probably due to the timing of aphid infestation. If aphids arrive after the 6- to 8-week period of protection provided by the chemical, then the insecticide will have minimal effect.
Note: This article is based on K-State Plant Pathology’s Fact Sheet “Barley Yellow Dwarf,” at: http://www.ksre.ksu.edu/library/plant2/ep165.pdf