Iris virus detected early in Treasure Valley onion fields
ONTARIO, Ore. — The iris yellow spot virus, which can severely impact onion yields, has made an early appearance in the Treasure Valley.
Southwestern Idaho and Eastern Oregon produce about 25 percent of the nation’s fresh bulb onion supply and the virus normally appears in onion fields in this region later in the summer.
But it was detected in commercial bulb fields in Payette County, Idaho, June 12 and in Malheur County, Oregon, last week, said Oregon State University Cropping Systems Extension Agent Stuart Reitz.
The advanced symptoms seen on some of the infected onion plants suggests they were probably infected around the first of June, he said.
“That would be really early,” said Oregon farmer Bruce Corn, who said the virus can devastate onion fields.
“It can take a whole field out in a pretty short amount of time,” he said.
The virus is transmitted to onion plants by thrips and growers are being encouraged to aggressively manage the tiny insects.
“Keep vigilant about watching what’s happening in your fields,” Reitz said. “Don’t wait until you get a full-blown infection across your field.”
Reitz said thrips populations didn’t experience their normal die-off rate this year because of a relatively mild winter and he believes that is a factor in the early appearance of the virus.
The mild weather also permitted the survival of more volunteer onions, which allow thrips to over-winter, he said.
The region faced less virus pressure than normal last year and a big reason for that was onion farmers sprayed for thrips earlier and more often, said Nyssa farmer Paul Skeen, president of the Malheur County Onion Growers Association.
Skeen said it’s critical that growers stay on top of their thrips management programs. Skeen, who has farmed for 43 years, used to never spray before the first of June but sprayed two times before that date this year.
“If people are not staying on top of their spraying, they’re going to get in trouble” he said.
Skeen said his fields are free of the virus but he’s also spraying a lot, which raises his production costs substantially.
“We’re at the point now where we’re spending more money trying to fight back the thrips than we do on fertilizer,” he said.
Plant health plays a major role in controlling the impact of the virus, Reitz said, since healthier plants are less susceptible to it.
Growers can minimize the stress on their onion plants by ensuring they have adequate moisture and fertility levels, he said.
“It’s every bit as important to try to minimize the stress on your plants,” said Corn. “If you can keep your plants healthy, (the virus) seems not to be as devastating.”
Despite the early appearance of onion farmers’ main production challenge, the region’s top cash crop looks good so far, Skeen said.
“For the most part, the onion crop looks very good and it looks healthy,” he said.