THE EFFECTS OF SOFT INSECTICIDES ON THRIPS POPULATIONS IN RED ONIONS

Lynn Jensen, Malheur County Extension Service, Clinton Shock and Lamont Saunders, Malheur Experiment Station, Oregon State University, Ontario, OR

Red onion has been grown in the Treasure Valley production region of Idaho-Eastern Oregon for many years. The quality of red onions coming out of the valley is generally very high, but the past three years have seen small quality problems related to thrips damage in storage. Thrips damage on red onion bulbs has been reported from most production areas of the world and is a relatively new problem, having developed over the past 6 to 10 years. Many ideas have circulated about why this problem has recently arisen. One theory is that widespread use of synthetic pyrethroid insecticides, which are toxic to predatory insects has reduced the availability of late season predators to prey on thrips. Over the past three years, an alternative approach to controlling onion thrips has been developed at the Malheur Experiment Station. This program consists of straw mulch for predator habitat plus the use of soft insecticides to suppress thrips while leaving predators to feed on the residual thrips population. This program has been very successful in controlling thrips and increasing bulb size and yield. In 2003, a trial was established to investigate the effects of an alternative program on yield and storage damage on two red onion varieties. The alternative program gave better overall yield and lower thrips damage that either the untreated check or the standard treatment.

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