Barley Yellow Dwarf (BYD) is a viral disease that can reduce yields in wheat, barley, and oats. The virus can infect numerous species of grasses including those you may find in ditches, pastures, and lawns. The virus is transmitted by aphids, which can acquire the virus and transmit it to other plants for many weeks afterwards. If aphids are carrying the virus and they infest wheat or barley fields, yield losses may occur. Research indicates that early infestations of winter wheat and barley in the Fall can be particularly damaging, as the virus may reduce tiller development and overall yield.
Unfortunately determining the effects of BYDV on crops is no easy task. Different species of aphids can transmit different strains of the virus, and different strains of the virus may vary in how much damage they cause to a plant. In addition, grass species and varieties vary significantly in their responses to BYD, meaning that one variety may be severely affected, whereas another may not. Lastly, one does not know if the aphids in your fields have BYD or not. Surveys from the last three years in Delaware indicate that BYD can occur at low levels, but that some fields appear to have more issues than others. This may be due to local reservoirs of grasses carrying the virus that allow aphid “green bridges” thereby increasing the chance that BYD may occur the next time barley or wheat is planted in that particular field. In fields with a history of BYD, growers may consider management options.
In the West, BYD is a significant, persistent, yield limiting factor in small grain production. This likely is due to the vast acreages of small grains and pastures planted in the region. Recent research from Kansas State University examined the effects of insecticide seed treatments, variety, and planting date on BYD severity and yield. Studies were conducted from 2011-2015 and included 1) Planting date- early (9-13 Sep) or late (10-18 October); 2) variety (3-8 were tested, depending on the year); 3) BYD pressure, which was achieved by sowing untreated seed (diseased control), sowing seed treated with Gaucho seed treatment at the highest labeled rate, or seed treated with Gaucho at the highest labeled rate and sprayed with Decathlon applied 8-9 times over the growing season (healthy control). Treatments were crossed in a split plot design. Each study was replicated twice each season. Researchers assessed the incidence of BYD symptomatic wheat plants when symptoms first appeared at weekly intervals until senescence. This was used to generate the rate of disease increase over the growing season (the Area of Disease Progress calculated using standard protocols). Plots were harvested, and yields determined. Data was standardized each year by expressing yield loss as a proportion of the healthy control, to account for yearly differences in disease pressure and variety.
The data showed that there was a linear relationship between disease progress and yield loss, with about 1% loss per each unit increase in disease progress. Planting cultivars with higher levels of BYD tolerance resulted in BYD symptom reduction of 80.9% and yield loss by 72.6% compared to susceptible varieties. Late planted wheat reduced BYD symptoms by 47.9% and yield loss by 57.5% compared to early planted wheat. Finally, Gaucho seed treatment reduced BYD symptoms by 35% and reduced yield losses by 16.4%. When all three methods (tolerant variety, late planting, seed treatment) were combined, BYD was reduced by 95.2% and yield losses reduced by 97.1% compared to untreated controls.
Although the situation is more severe in the great plains, the data show that BYD can be managed by variety selection, planting date, and seed treatment (if early Fall infections occur). In Delaware we do not have evidence that Fall infections occur commonly, at a significant yield limiting level, or at a large scale. However, concerned growers can still choose tolerant varieties, available from the Virginia Tech Small Grains Program, which are effective regardless of when viruliflous aphids arrive in fields, as well as avoiding early planting early in fields with a history of BYD issues. Seed treatments could be beneficial in some instances. These products have a limited window of effectiveness and initial infections will occur, but the disease progress, if these aphids were carrying virus and arrived during the time when the chemical was effective, will be delayed. This should be kept in mind when considering these additional inputs to small grains.