Whitefly Growth Regulators: Large-Scale Evaluation

Abstract

Two insect growth regulators (IGRs) that are selective against whiteflies (Aleyrodidae) became available for the first time in 1996 to Arizona cotton growers under emergency exemption. These IGRs were studied in a commercial -scale whitefly management trial (178 acres) in 1996. The trial was designed to evaluate provisional whitefly recommendations. Three sets of factors were tested in a 48 plot factorial design: application methods, thresholds for initiating IGR use, and insecticide regimes. Ground (broadcast at 15 gallons/acre) and aerial applications (5 gallons/acre) were roughly equivalent over a wide range of variables examined (whitefly populations, number of sprays, cost, and yield). Under the higher population densities, ground applications sometimes suppressed whiteflies to a greater extent than aerial applications. The rapid advance of the population resulted in the initial triggering of all thresholds within just five days. No consistent trend in population suppression was seen for the thresholds tested (0.5, 1.0 and 1.5 large, visible nymphs per 3.88 sq cm leaf disk located between the major and first, left lateral vein of the fifth main stem node leaf below the terminal). The control cost for the highest threshold was significantly less than for the middle threshold, but not for the lower threshold. Under emergency exemption, each IGR may be used only once per season. The sequence of use did not result in any consistent advantage in population suppression, cost, number of sprays needed, or yield. The IGR regimes were in general more efficacious, less disruptive, and less costly than the conventional insecticide regime. There were significantly fewer sprays needed by the IGR regimes compared to the conventional regime. All regimes successfully controlled whitefly populations for a 12 week period and cost significantly less than conventional programs tested in 1995 (Ellsworth et al. 1996a). IGRs are effective, long-lasting, and less environmentally disruptive alternatives to conventional insecticides. They reduce the risk of secondary pest outbreaks and pest resistance, and increase the opportunity of natural enemy conservation.