Barley yellow dwarf infections in wheat
One of the most common wheat disease problems in Kansas this year was barley yellow dwarf. Some questions have arisen about this. One of the questions is why was barley yellow dwarf has been so widespread when there didn’t seem to be many bird cherry-oat aphids or greenbugs reported. This is a good question, but I don’t think anyone has any answers. The only explanation is that the aphids and greenbugs had to have been present in the regions where barley yellow dwarf has occurred, just at low population levels. Those are the two primary vectors of barley yellow dwarf on wheat. It doesn’t take a very high population of aphids to introduce and spread the virus.
There is no indication of a new variant of the barley yellow dwarf virus that is more virulent than what we’ve had in the past. In our variety screening for barley yellow dwarf reactions of wheat, the varieties have reacted this year the same as they have in previous years. There are eight known strains of the barley yellow dwarf virus, but only two that infect wheat in Kansas. Those two are known as the PAV and RPV strains. Of those two, the PAV is more prevalent, but it doesn’t make much difference. Both strains cause similar symptoms and yield reductions in wheat. The strains of the barley yellow dwarf virus that infect wild grasses such as big bluestem are different than the strains that infect wheat. Each strain of barley yellow dwarf virus is vectored by specific species of aphids. The PAV and RPV strains that infect wheat are vectored by the oat-bird cherry aphid and greenbug. Other strains, that infect other grasses, are vectored by different aphid species.
The barley yellow dwarf infections at our variety screening trials near Manhattan were fall infections. We maintain “clean” plots for comparison purposes in both the fall and spring. Where we used an insecticide seed treatment in the fall and sprayed for aphids and greenbugs every 2-3 weeks in the fall, there was a big difference between the treated and untreated plots in the level of barley yellow dwarf infection. Where we waited until late winter and early spring to spray for aphids and greenbugs every two weeks, there was very little difference between the untreated and treated plots in the level of barley yellow dwarf infection.
If the infected plants show yellowing symptoms but are not stunted, the level of yield loss will probably not be as great as where the plants were stunted. When barley yellow dwarf causes both yellowing or purpling (the nature of the discoloration depends on variety) and stunting, yield losses can be as much as 30-35 percent or more. When the disease causes yellowing or purpling but with little or no stunting, yield losses will usually be limited to about 15 percent or less.
We screen varieties for their reaction to barley yellow dwarf infection based on the visual symptoms. We also have a test nearby with a smaller number of varieties in which we take yield data. In our tests, the level of visual symptoms corresponds closely to the level of yield reduction. The varieties with the best visual ratings against barley yellow dwarf are: 2137, 2174, Coker 9663, Duster, Endurance, Everest, Overland, Overley, Pioneer 25R47, Roane, Sturdy 2K, Truman, and Winterhawk. Some of those are soft red winter wheat varieties.
Other than variety selection, there are a couple other good, effective means of managing this disease. Producers could use seed-treatment insecticides, but these treatments are expensive and usually only give about 50 percent control. Planting after the Hessian fly-free date is another management strategy.
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