A ONE YEAR STUDY OF THE EFFECTIVENESS OF OXAMYL (VYDATE l) TO CONTROL THRIPS IN ONIONS WHEN INJECTED INTO A DRIP IRRIGATION SYSTEM

Lynn Jensen, Eric Feibert, Clint Shock and LaMonte Saunders

Malheur County Extension Office, Malheur Experiment Station, Oregon State University, Ontario, OR, 2004

Onion thrips and western flower thrips are the main insect pests on onions grown in the Treasure Valley production area of Idaho and Eastern Oregon. In this region about 3000 acres of onions are grown under drip irrigation. Because of the increased yield and quality of onions grown under drip irrigation this management practice is increasing on lands that were formerly marginal to onion production. It is a common practice to inject the systemic insecticide oxamyl (Vydate L) into the drip lines on a weekly or biweekly basis to control thrips. Most of these growers also apply 2-6 foliar insecticide applications in addition to the oxamyl applications. Most growers feel there is an economic advantage to the additional oxamyl applications even though the additional cost is about $150/acre. This trial was designed to determine the effectiveness of oxamyl at two different application rates and in combination with two foliar insecticide programs.

The oxamyl plus alternative insecticides (azadirachtin + spinosad) gave significantly better thrips control than any other treatment and had the highest yield of colossal, super colossal and total yield. All of the treatments with foliar insecticides gave significantly higher colossal yields compared to the oxamyl only and the untreated check. Oxamyl treatments applied as 1.0 qt weekly or 2.0 qt every other week were no better than the untreated check. One year’s data would suggest that oxamyl is not contributing to thrips control.

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