Idaho onion drip trials help control thrips

Sean Ellis

Capital Press

University of Idaho researchers have found that applying pesticides through a drip system helps control thrips populations in onion fields early in the growing season. But they're still trying to find an application program that works all season long.

PARMA, Idaho — Drip irrigation trials designed to help onion growers better control thrips have proven successful in keeping the insect’s populations low early in the season.

But University of Idaho researchers are still trying to find a drip application program that controls thrips numbers all season long.

Drip application systems in the trials “are doing a better job early in the season of controlling the thrips, but we don’t have a strictly drip-applied program we can use all season long to keep thrips populations low,” said Mike Thornton, superintendent of UI’s Parma research and extension station.

The Parma trials are looking at whether applying pesticides through a drip irrigation system is a better and more efficient way than foliar applications to control thrips, which are a vector for the iris yellow spot virus, the main pest for onion farmers.

There is a lot of interest in the trials because of their potential to help growers control thrips, said Idaho farmer John Hartman, who has 90 percent of his onions on a drip system.

“Thrips are a huge problem,” he said. “They chew on the plant and it gets gray and unhealthy. Once that happens, you lose a lot of your yields.”

About 50 percent of the onion fields in Idaho and eastern Oregon now use a drip system.

Besides reducing worker exposure to pesticides and being environmentally friendly, injecting pesticides through a drip system puts the chemical down in the onion tissue where the insect feeds, which is hard to do with foliar application, Thornton said.

He said researchers will continue to look for the right drip application program that can control thrips populations throughout the growing season. “We would really like to be able to give growers a season-long drip program that they could use.”

This was the third year of the trials, which cost about $25,000 annually and are being funded by Idaho and Oregon onion associations.

Data from this year’s trials are being evaluated and will be released to Idaho and Oregon onion growers during their joint annual meeting in February.

Researchers said they have found that a drip application program helps optimize plant health because it allows the right amount of water and fertility to be applied at the right time.

“A healthy plant withstands thrips pressure better. I’m really impressed with the plant health improvement that we’re getting with some of those treatments,” said Bill Buhrig, a crop extension agent with Oregon State University’s extension office in Ontario who oversaw the Parma onion trials.

Thornton said applying pesticides through a drip system has helped keep up populations of beneficial insects that feed on thrips, such as the minute pirate bug. General foliar applications tend to kill everything in the field, he said.

“We’re not convinced the (pirate bug) populations are high enough by themselves to control the thrips but (drip applications) are helping to keep those good bugs in the field and not killing them off,” Thornton said.


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