How Often Should Onion Growers Spray For Thrips?

Dry bulb onions contribute more than $120 million to the Treasure Valley’s economy in eastern Oregon and southwest Idaho.

To help these growers get the most out of their crops, while ideally reducing inputs, Oregon State University partnered with Greenway Research and Consulting in Parma, ID to conduct field trails from 2019-2021.  Researchers focused on fertilizer use as well as insecticide applications.

Making Fewer Applications Is Best

When it comes to insecticides, Stuart Reitz, Director of OSU’s Malheur Experiment Station said applications are key to stave off onion thrips, but a calendar-based spray program is not always the best.

“But in some years, we can cut back on the number of applications with our threshold-based scouting and say, ‘okay, we don't need to spray today. We'll come back and look again later and decide whether we need to spray’," Reitz said.  "And so we can go through the sampling routine and better time insecticide applications. So again, the grower is making fewer applications, but still winds up with a large, high-quality crop.”

It's About Saving Farmers Money

Reitz added they tested three insecticide strategies; no insecticide, weekly calendar-based sprays, and IPM (Integrated Pest Management) strategies only when thrips numbers exceed a damaging threshold.  He said while not always the top performer, the IPM approach offered solid results while reducing the number of sprays.

“Just the importance of trying to time those insecticide applications and can help growers, again, save those application costs, the costs of the insecticides, and still be able to grow as good a crop as they would with additional insecticide applications that may not be benefiting them all that much,” Reitz said.

Click Here for the results of OSU's testing.

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