Sean Ellis/Capital Press
ONTARIO, Ore. — Iris yellow spot virus pressure in this region has not been nearly as bad as it was last year, when it wiped out some onion fields.
“The virus seems to have been held off well this year,” said Paul Skeen, who farms near Nyssa, Ore.
Farmers in the Treasure Valley area of southwestern Idaho and eastern Oregon produce about 25 percent of the nation’s bulb onions and the virus is one of their main production challenges.
It weakens the plant and reduces onion production. It can substantially reduce onion bulb size, which is important because larger onions fetch a higher price.
The disease is spread to onions by thrips, and Skeen said many growers in the area started spraying for thrips earlier this season and they sprayed more often.
Skeen started spraying 10 days earlier and sprayed every seven to 10 days as opposed to every 14-20 as he has done in past seasons.
“I’ve got a good crop coming because I stayed on top of it. I think everybody’s been doing that,” he said. “I still have one 15-acre field I’m a little nervous about but last year at this time we were concerned about half our fields.”
While onion growers in the Treasure Valley area typically start their thrip spraying programs around Memorial Day, many started in early May this year, said Stuart Reitz, an OSU cropping systems extension agent in Malheur County.
While onion growers in this area normally make about six applications for thrips in a season, many have made eight or nine already this year and a few are up to 10, he said.
“That helped keep the thrips population down,” Reitz said.
With onion season winding down, thrips pressure is starting to drop off as the plants mature, Reitz said.
“This year hasn’t been nearly as bad as last year for the virus and I think part of the reason is last year was so bad that people were more on guard this year,” he said.
The severity of iris yellow spot virus epidemics varies from year to year and virus pressure has been particularly bad in this area the past several seasons.
“We needed this year. It was nice to have a year like this, to this point, that hasn’t been nearly as crippling,” said OSU cropping systems extension agent Bill Buhrig.
Buhrig believes a mild start to the season helped onion plants establish good health, which made them less susceptible to the virus.
“We didn’t get really hot, nasty weather until we rolled into July,” he said. “By that time, good plant health was established. When you have good plant health, the plant can handle more thrip pressure.”