Onion thrips appear early in Treasure Valley
NYSSA, Ore. — Onion thrips were found in commercial fields in the Treasure Valley region in late-April this year, much earlier than normal.
Thrips are a vector for the iris yellow spot virus, which can severely reduce onion yields. The virus was detected in onion plants the last week of May and researchers said they were likely infected in mid-May.
Onion growers in this area historically haven’t been concerned about thrips until about Memorial Day and the virus in past seasons has made its initial appearance in July or early August, said Oregon State University Cropping Systems Extension Agent Stuart Reitz.
The virus was detected the first week of June last year, which was an extremely early appearance, he said.
“They’re just coming earlier every year,” Reitz said, a development he contributed to the recent warmer than normal winters and early springs. “I think more of their populations survived over the winter so they were out spreading the virus around earlier than we’ve seen in past years.”
There are no good biological methods for controlling onion thrips in the Treasure Valley area of Southwestern Idaho and Eastern Oregon, which produces about 25 percent of the nation’s fresh bulb onion supply.
The only effective way to control them is by spraying.
With their earlier appearances, that means growers have to spray more to control them.
“If growers are having to spray another month of the season, that’s another huge cost for them,” Reitz said.
Thrips, and the virus they transmit to onion plants, will devastate an onion field if not controlled and not spraying is not an option, said Oregon farmer Bruce Corn.
“Sometimes you have to close your eyes to the cost because you won’t have a crop if the virus gets in early and you don’t spray for it,” he said. “As a grower, if you expect to have a crop, you have to be very vigilant and proactive on it.”
Spraying for thrips costs between $20 and $100 an acre, depending on what chemical is used, according to Corn and Paul Skeen, president of the Malheur County Onion Growers Association.
Because there are a limited number of chemicals available to growers that effectively control thrips, rotating them is critical to avoid the insects building up resistance to them, Corn said.
That means growers have to also use the more expensive chemicals and Skeen estimates the average cost of spraying is about $50 an acre.
“If you’re spraying eight times, that’s a lot of money,” he said. But, he added, “You won’t have a crop if you don’t.”
To try to find a solution to the thrips problem, OSU researchers in Ontario last year started a field trial with some experimental onion varieties to see if they offer some resistance to thrips and the iris yellow spot virus.
Some of the varieties showed promise, Reitz said, but it will take several years to test them some more, then isolate the beneficial traits and breed them into commercially accepted varieties.