Whitefly Management in Arizona: Looking at Whole Systems

Whiteflies remain a threat to production of cotton in Arizona. Looking at a series of commercial -scale trials, levels last season were delayed compared to previous years, but at higher densities than in 1995, an outbreak year. Efforts must be expended to optimize insect growth regulator (IGR) use and integrate these tactics with other aspects of crop and pest management. Broad spectrum insecticide use prior to treatment for whiteflies with IGRs alters the ecology of the system. Whitefly densities consistently increased after disruption with a Lygus insecticide relative to Lygus -untreated areas. While Lygus control is a production imperative, guidelines are presented for minimizing the impact of this disruption. The modes of action for the two IGRs differ substantially and result in subtle changes in population age structure and dynamics. The consequences of these changes impact natural enemies and should be noted by producers when selecting an IGR or monitoring populations after treatment. Retreatment after initial IGR sprays depends on many factors. While apparently similar levels of suppression are possible when only one IGR is used, regimes using both available IGRs resulted in the fewest number of damaging large nymphs late in the season, just prior to defoliation. Conventional insecticides rotated according to pre-IGR introduction guidelines (`95IRM') also suppressed populations significantly and comparably to IGR regimes until late in the season. Then, whitefly densities rose aggressively just prior to defoliation and pyrethroid susceptibility was significantly reduced in the 951RM regime. Full adoption of IGR -based technology along with `Bt' cotton allows growers to better manage whiteflies with fewer disruptions which can lead to secondary pest outbreaks, pest resurgence, and insecticide resistance. Introduction Whitefly management in Arizona has advanced to such a degree in the last few years that scientists, practitioners, and growers are challenged to further refine ourunderstanding and improve all aspects of management of this pest. Part of this understanding and improvement is best served by stepping backand examining whiteflies within whole systems. While Arizona has enjoyed huge gains in whitefly control, control cost reduction, and cotton quality (Tables 1 and 2), we must continue to improve adoption of our best technologies and strategies for coping with all our pests. Dramatic reductions in the number of sprays against whiteflies (Table 1) and the whitefly control proportion of the total insect control budget (Table 2) has shifted the focus off of this key pest in our system and contributed to some complacency in the grower community. For example, overall insect growth regulator (IGR) usage was down by 30% in 1997 (about 170,000 application -acres) as compared to 1996 in spite of heavier late season whitefly pressures and a 30 -day increased IGR -use window this past year. Of the 1.81 sprays used against whiteflies, only about 0.5 sprays were IGRs. This is invaluable chemistry in our system and our studies are aimed at optimizing their use for whitefly management and integrating this technology within whole systems of integrated pest management. Examination of insect control dynamics as part of whole systems is key to the development of information relevant to grower experience and the validation of pest management recommendations.