Some reports of what seems like fairly high incidence of barley yellow dwarf virus (BYDV) are coming in from fields in some parts of the state. Some of these fields reportedly have as much as 20% of the plants showing symptoms typical of BYDV –leaves with yellowish to reddish-purple tips. These symptoms may sometimes be confused with nutrient deficiency, and in some cases. In addition, damaged leaf tips resulting from the freezing temperatures we had a week ago may also be misdiagnosed as a virus disease. On the other hand, plants without visual symptoms may be virus infected. For instance, although characteristic of BYDV, leaf discoloration may be absent in some cases, with infected plant showing reduced growth and normal-looking leaves. Severe stunting of plant is more common when infections occur early in the fall during the seedling stage, whereas discolored leaf tips are more typical of late infections.
This disease is caused by several closely related viruses which are transmitted by more than 20 different species of aphids. BYDV tends to be most severe in fields planted before the Hessian fly-free date when the aphid population is high. Once infections occur, there is very little that can be done. No fungicide will control BYDV, and insecticides applied after infection will reduce the aphid population but will not prevent the disease from developing. The residual effect of the insecticide may not last long enough to protect against subsequent buildup in the aphid population. During active feeding, a few aphids will be enough to transmit the virus from one plant to another.
Yield reduction due to BYDV is generally greater when infections occur in the fall than in the spring. However, late infections may still lead to yield reduction, since severely infected plants may produce smaller heads and kernels and fewer spikelets per head. It is difficult to estimate the level of damage caused by BYDV at this time. Since grain fill is still about a month away, there is no way of knowing whether kernels on sick plants will be smaller and how much smaller. However, you can use the number of healthy-looking tillers per foot of row as a guide. The same way that yield potential is reduced if tiller numbers fall below 25 per square foot, yield potential may also go down if the number of healthy plants per square foot falls below 25. Sick plants will yield less than healthy plants. “Pick about 10 to 15 spots in the field and count the number of healthy-looking tillers per foot of row. A stand with an average of about 15 tillers per square foot is considered minimum for an economic crop” (http://corn.osu.edu/newsletters/2015/2015-06).
For more on BYDV, visit the field crops disease website at http://www.oardc.ohio-state.edu/ohiofieldcropdisease/.