Iris yellow spot virus detected in volunteer onions
ONTARIO, Ore. — Oregon State University researchers have alerted onion growers in the region to be on the lookout for the iris yellow spot virus in this year’s crop.
The virus has been detected in several volunteer onions, said OSU Cropping Systems Extension Agent Stuart Reitz.
“I haven’t seen it in the crop yet but if we’re seeing it in the volunteers, it’s only a matter of time before it shows up in the crop,” he said. “I expect to see it showing ... up in the crop any time basically.”
About 25 percent of the nation’s fresh bulb onions are grown in Eastern Oregon and Southwestern Idaho and the virus is one of the industry’s top production challenges.
It weakens the onion plant and can significantly reduce growth, which is important in the onion industry because larger-sized bulb onions fetch higher prices.
The virus is transmitted to onions by thrips and the insect’s populations are starting to build up rapidly, Reitz said.
“We’re consistently seeing 1 to 2 adult thrips per plant, which is a healthy population for this time of year,” he said.
The virus was detected in last year’s crop in early June.
Reitz said growers should be focusing on controlling volunteer onions, since they act as early season reservoirs for thrips and the virus to move into the crop.
“People need to get all of the volunteer stuff away,” said Nyssa farmer Paul Skeen, president of the Malheur County Onion Growers Association.
Nyssa grower Reid Saito said the virus is one of the industry’s top two problems, along with the nutsedge weed.
“We don’t have a real good handle on it,” he said. “You just never know when it’s going to show up. Year to year and area to area, the virus pressure varies.”
Saito said he has seen onion fields that look great “and then when the virus shows up, I’ve seen the whole complexion of the crop change from good to terrible in a matter of days.”
Reitz and Skeen credit an aggressive thrips control program with helping keep virus pressure low last year compared with the previous several years.
2013 was a bad year for the virus but last year was mild by comparison, Skeen said, and that was due in part to farmers spraying earlier and more often for thrips.
Farmers should be out scouting their fields now and acting quickly if any virus pressure is detected, Reitz said.
“People should be checking their crop very carefully to see if any virus shows up,” he said. “The people who had less severe pressure last year were the ones who stayed on top of it.”
For more information about thrips and the virus, contact Reitz at (541) 881-1417.