Thrips resistance management in California ornamentals

The western flower thrips, Frankliniella occidentalis Pergande, remains a serious pest of ornamental plant production in California. What exacerbates the problem is that they possess the innate ability to become resistant to the common pesticides used for their control. New chemical classes with thrips control potential are few and far between, and existing chemicals continue to dwindle. One of the most effective active ingredients against thrips on the market today for control of thrips is spinosad (Conserve). Unfortunately, continued use and off label use of spinosad and other common products has resulted in populations of western flower thrips that are nearly impossible to control with current registered chemicals. Further, ornamental plant producers that supply finishing growers with plugs and cuttings are under greater scrutiny for invasive pests, and the detection of thrips in a shipment is a reason for concern. This leads to extraordinary efforts to control thrips at these facilities. Unfortunately, when a thrips population is carried with the product to a new site, it already possesses a high level of tolerance for pesticides, which means finishers will have difficulty in attempting to control thrips on site. We have been monitoring western flower thrips populations from ornamental plant producers for spinosad resistance in southern California for several years. Thrips from facilities that are using spinosad sparingly or not using it at all have thrips populations that are quite susceptible to the product. Growers that are using spinosad routinely for thrips control are showing high levels of resistance. In addition, thrips from these facilities are very difficult to control, even with a broad spectrum of pesticides. A summary of the results of our studies and suggestions for thrips management will be presented.