| Summary: | Monitoring of whitefly resistance in the major cotton producing areas of Arizona confirmed the presence of an over 100 fold resistance to the mixture of Danitol® + Orthenem (fepropathrin + acephate). Strong evidence was found of cross-resistance affecting the other principle pyrethroid insecticides used to control whiteflies (Asana®, Capture® Karate®). Susceptibility to Ovasyn® varied widely in leaf -disk bioassays; lesser variation was observed in whitefly susceptibility to endosulfan. A provisional resistance management strategy (IRM) for Arizona whiteflies was formulated and evaluated in a 200 acre field trial in 1995. A key element of the strategy was diversifying as much as possible the insecticides used against whiteflies. Contrasts of this (rotation) strategy with a more conventional (less diverse) regime showed that rotation slowed but did not prevent resistance from developing. By seasons end both the IRM and conventional plots had very high and comparable levels of resistance to Danitol® + Ortliene®. This large field trial illustrated clearly the seriousness of the whitefly resistance problems faced in Arizona. It showed that whitefly populations cannot be managed effectively solely with the products currently registered for this purpose in Arizona. The large shift to lower susceptibility took place with as few as 3 insecticide treatments. In concert, our field art laboratory results indicated unequivocally that Arizona growers will be forced by resistance to greatly reduce reliance on pyrethroid insecticides in the future. This underscores the urgency for obtaining approval of novel new insecticides for whitefly control and for deploying new products within the framework of a resistance management strategy that limits their use.
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