An aphid carrying the barley yellow dwarf virus has been making itself known in Manitoba this year.
The bird cherry-oat aphid is the main suspect when it comes to spreading the insect-carried disease, which does not spread through dirt or seed.
Why it matters: While barley yellow dwarf virus, or “red leaf” when it’s found in oats, can mimic other crop stresses, the presence of bird cherry-oat aphid can alert producers to a positive viral infection.
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One case of the virus has been confirmed in an eastern Manitoba oat crop this year. Another case in a barley field has not been confirmed. The carrier aphids have been seen more frequently than have infections.
“I’m getting more and more reports,” said provincial entomologist John Gavloski, adding it has not been a big year for bird cherry-oat aphids.
The province saw a worse year for the virus in 2017, when a number of fields were infected in central Manitoba around Carman, Elm Creek and parts of the Red River.
Disease details and scouting
According to the July 27 provincial pest report, any small-grain cereal crop is vulnerable to the virus. The aphids pick up the pathogen from reservoirs in native or weedy perennial grasses, said David Kaminski, field crop pathologist with the province. From there, the virus transmits to cereal crops.
Early stages cause green to fade from leaf edges and tips, often leaving a central green strip, the Co-operator wrote back in 2017. In oats, the discoloration often appears red, pink or purplish. Advanced infections cause premature ripening, stunted plants and unfilled or missing grain heads.
“Be careful in your diagnosis though,” the pest report warned. “Without the vector [aphid] present, reddened or purpled leaves are likely the result of environmental stresses.”
Producers scouting their field should be on watch for a dark green aphid with a telltale brown patch at the base of the abdomen, but it may require a magnifier to spot it, said Gavloski. If it has the dark patch and is on a cereal crop, it’s likely the bird cherry-oat aphid.
“You’ll likely see all stages on a crop at a given time,” Gavloski said, noting the species reproduces constantly and has multiple generations. The species blows into Manitoba in spring.
The economic threshold for aphids in cereals is 12 to 15 aphids per stem prior to the soft dough stage, he added.
Once in the field, there are no practical mitigation options for barley yellow dwarf virus, Kaminski said.
“The severity of the disease, especially the stunting, (is usually) evident once the crop has headed out.”
He added that he is not aware of environmental conditions that exacerbate that severity, although plants short of water as they mature may show more evident signs of the disease.
– With files from Alexis Stockford
