Onion field trial seeks optimal thrip-control program

Onion growers and industry representatives inspect an onion field trial at Oregon State University's Malheur County experiment station July 8. The trial is trying to help growers reduce the number of times they spray for onion thrips.

ONTARIO, Ore. — Oregon State University researchers in Eastern Oregon are trying to help onion growers figure out which mix of insecticide treatments is most effective, and economical, for controlling thrips populations.

Researchers are rotating chemistries, using them at different times of the season and applying them in varying intervals, said Stuart Reitz, an OSU cropping systems extension agent.

Onion thrips cause feeding damage and are also a vector for the iris yellow spot virus, which can significantly lower onion yields.

There are no good biological controls for the insects and onion growers say that not spraying for them in this region isn’t an option.

“Onion thrips are a bigger problem than anything else in onion production,” Reitz said. “If you don’t do anything to manage thrips in the Treasure Valley, you’re not going to have very good onions.”

Onion growers used to spray three or four times a year for thrips but in recent years they have had to spray as many as eight to 10 times in a season, said Nyssa farmer Paul Skeen.

“The key ingredient in controlling thrips is getting on it early and keeping their populations down,” he said. “When in doubt, you spray.”

But each treatment costs money and the main goal of the OSU trial is to try to find a season-long control program that will allow growers to reduce the number of times they spray, Reitz said.

Researchers are also trying to determine if products have a longer residual effect at certain times of the season. If they do, growers could get by with spraying less often.

“It’s getting so costly to control them and we want to see if we can reduce that cost for growers,” he said.

There are only six products that are effective for controlling onion thrips and researchers also want to develop a treatment program that allows growers to rotate chemistries often to avoid insect resistance, Reitz said.

Malheur County farmer Bill Johnson said the ongoing OSU trial is helping growers zero in on the optimal treatment program for thrips.

“We continue to have issues with flexibility in some of the chemistries we work with,” he said. “We’re just trying to find the right mix of chemistries. There are a lot of complexities (involved).”

This year’s trial includes some experimental onion varieties that could have resistance to thrips.

The varieties come from New Mexico State University’s onion breeding program, which wants to see how they perform in an area with strong thrips pressure, and the early results are encouraging, Reitz said.

“We seem to be seeing lower numbers of thrips on some of these experimental lines,” he said.

If any of the varieties do have genetic resistance to thrips and that trait can be bred into commercially acceptable lines, that would help onion growers in this region immensely, Reitz said.

“It would have huge benefits all around, helping growers’ bottom line as well as avoiding problems like insecticide resistance,” he said.

Recommended for you