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Thrips found on volunteer onions

Thrips have been found on volunteer onions in fields in Eastern Oregon and Southwestern Idaho. Researchers are advising growers to control the volunteer onions before this year's onion crop begins to emerge.
Sean Ellis

Capital Press

Published on April 21, 2014 10:24AM

ONTARIO, Ore. — Researchers are alerting onion growers that worrisome levels of thrips have been found on volunteer onions in Eastern Oregon and Southwestern Idaho.

Onion thrips are a vector for the iris yellow spot virus, the main pest problem for onion farmers in this region.

Volunteer onions left over from last year’s crop can act as an early season host for thrips, which can then infest newly emerged onion fields located nearby.

Thrips have been found on volunteer onions in Malheur County in Oregon and Canyon and Payette counties in Idaho, said Stuart Reitz, a cropping systems agent at Oregon State University’s Ontario Extension Center.

Reitz also found thrips on sticky traps placed around those fields.

“We just want to let people know what’s happening and to get them paying attention to what’s going on in their fields,” Reitz said.

He said growers should control volunteer onions, especially those in fields that were heavily infected last year, before this year’s onions begin to emerge in nearby fields.

Controlling thrips early in the season is important, said Mike Thornton, a plant physiologist at University of Idaho’s Parma research center.

“Don’t assume it’s too early,” he said. “Always be out scouting your fields to make sure you don’t have thrips populations starting to establish.”

Iris yellow spot virus was a major problem in this region last year and OSU and UI researchers are working closely with growers to try to prevent a repeat in 2014, Reitz said.

The virus, which is a stress on the plant and affects onion growth, created a lot of damage in 2013, he said.

“Some fields were wiped out,” he said. “They were complete losses.”

Infected plants won’t produce as big a bulb as uninfected plants, he said, and infected onions also tend not to store as well because the neck of the onion doesn’t seal properly, providing a potential pathway for bacterial pathogens.

When a lot of the virus gets into a field, it can substantially reduce onion sizes, Thornton said. That’s important because larger onions fetch a higher price.

“If you don’t have the size, the economic consequences are pretty big,” he said.

Paul Skeen, who farms south of Nyssa, Ore., said the virus is one of the top challenges onion growers face because it can devastate yields.

Infected smaller onions that fell through the chains of harvesters last fall can create a bridge for thrips to infest this year’s crop, he said.

He said onion farmers should address the problem immediately.

“People need to get right on that and get that stuff tore up, sprayed or do whatever they have to do to get rid of them,” he said.


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