Whitefly management in Arizona: looking at the whole system

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. Re-treatment after initial IGR sprays depends on many factors. While apparently simular 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 95IRM 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.