Onion thrips population starts to soar in Idaho, Oregon
ONTARIO, Ore. — Onion thrips were late to arrive in the Treasure Valley of Idaho and Oregon this year, delayed by a harsh winter and wet spring.
But temperatures have been well above normal this month and the onion pest’s population is exploding as a result. The average high temperature in Ontario has exceeded 100 degrees eight times in July already.
“The heat’s making things explode,” said Nyssa grower Paul Skeen, president of the Malheur County Onion Growers Association.
Onion thrips can cause feeding damage and they are also a vector for the Iris Yellow Spot Virus, which can significantly reduce yields of the bulb onions grown in the region.
“They were a little late getting in but they have made up for it,” said Stuart Reitz, an Oregon State University cropping systems extension agent in Ontario. “With these higher temperatures, the populations are really going crazy. We’re starting to see a lot higher numbers.”
Virus pressure is just starting and has been detected in a few commercial fields recently, Reitz said.
“We haven’t seen much (virus) around the area. Yet. It’s probably coming,” he said.
While the timing of the pest’s appearance in the valley can vary from year to year, they are an annual headache for Treasure Valley onion farmers.
There are no effective biological controls for onion thrips, so that leaves the use of insecticides as growers’ only option to control them, Reitz said.
The thrips problem has only gotten worse for growers over the years, Skeen said.
“When I started farming here 45 years ago, if we sprayed four times in a season, that was a lot,” he said. “Now, it’s not uncommon to spray seven or eight times.”
Onion grower groups in the region are helping fund a field trial overseen by Reitz that seeks solutions to the thrips problem.
One of the main goals of the trial is to help growers find the right mix of insecticide treatments that allows them to spray as little as possible.
Researchers are rotating chemistries and using them at different times of the season to try to find the right combination for thrips control.
It costs between $20 and $100 an acre to spray for thrips, depending on which chemical is used, so reducing the number of times a grower has to spray can save a lot of money, Reitz said.
OSU researchers recommend not overusing any one chemistry to prevent resistance in thrips.
“You have to manage them in the season but you also have to look at the longer term picture and that’s why we’re really stressing rotating chemistries so you don’t have resistance building up,” Reitz said.
OSU researchers recommend not using the same onion thrips insecticide more than two times in a season and have adopted the slogan, “Two sprays and put it away.”
Controlling volunteer onions is also recommended.
“The longer the volunteers are out there, the more virus and thrips they are going to generate,” Reitz said.