Experts worry volunteers could support grain virus
By John O’Connell
TWIN FALLS, Idaho — After causing widespread damage throughout Magic Valley during last season’s cereal harvest, barley yellow dwarf virus appears to have been held in check this season.
But cereal grain experts worry about the next crop as recent rainstorms have created ideal conditions for volunteer wheat and barley plants that could support large populations of aphids, which vector the disease.
University of Idaho Extension entomologist Arash Rashed has received few inquiries from growers about barley yellow dwarf this season, and samples he’s tested have been negative. To avoid missing infections in testing, he’s ordered antibodies for two additional strains of the disease, though they’re not known to be prevalent in Idaho.
Barley yellow dwarf symptoms include stunting and yellow or red leaf tips. Rashed fears volunteers germinated following recent storms may help aphids bridge the gap between harvest and the sprouting of new fall grains.
“After harvest of summer crops, aphids need a place to go, and what is better than those volunteer wheat plants and weeds that are around?” Rashed explained.
He has research underway examining the relationship between the pathogen and symptom severity in various wheat cultivars.
Rashed had hoped to start an aphid monitoring program but couldn’t find the necessary funding. He remains hopeful about starting aphid monitoring within the next few years.
Rashed advises growers in areas of high risk for barley yellow dwarf to control volunteer plants, either chemically or mechanically. He said insecticidal seed treatments and delaying fall crop planting so emergence occurs after aphid flights have already passed by are also effective strategies.
Castleford, Idaho, grower Roger Wells said barley yellow dwarf cut yields in half in fall wheat he harvested last season.
“That was the first our Simplot field man said he’d ever seen it in this area,” Wells said. “We’re hoping it was just one of those years. The wheat this year looks a whole lot better.”
Last fall, Wells said he delayed planting this season’s winter wheat crop by a couple of weeks and also used an insecticidal seed treatment. He’ll take the same precautions this year, noting there’s a lot of corn, which can also support aphids, in his area.
Mike Erickson, a seed treatment specialist with McGregor Co. in Twin Falls, studied test plots in Kimberly during the 2012-2013 season and confirmed delayed planting is highly effective. Erickson, who shares Rashed’s concerns about ideal conditions for volunteer plants this fall, also documented a direct correlation between proximity to corn fields and yield reductions in wheat due to barley yellow dwarf.
Erickson studied fall wheat seeded on Sept. 15, with watering of individual 20-acre plots staggered over 10 days to stimulate germination at different times. Yields in crops watered at least eight days after planting were about 100 bushels per acre greater than the plots that were watered earliest.
That season, Erickson also analyzed commercial yields in Kimberly. Within the same infected grain fields, he said yields averaged 50-70 bushels per acre adjacent to corn, compared with 150-170 acres further away from corn.