Theory versus practice: are insecticide mixtures in Arizona cotton used for resistance management?^†

BACKGROUND: Resistance management in pesticide use is critical, yet grower practices, especially pesticide mixing motivations, diverge from theoretical frameworks. This study analyzes 30 years of Arizona cotton growers’ practices and pest manager insights to understand mixing trends. RESULTS: Growers predominantly mix pesticides for spectrum or efficacy, not resistance management. This highlights a gap between theory and practice, emphasizing the complexity of real-world dynamics. A shift over time towards selective insecticides and integrated pest management (IPM), supported by extension education, has reduced reliance on broad-spectrum insecticides and increased opportunities to conserve the natural enemies of key pests. This reduced the frequency of insecticide use, a mutual goal of both IPM and resistance management. The availability and adoption of selective products with diverse modes of action, along with the resulting increases in biological control and refuges, likely has delayed or prevented resistances without emphasis on using mixtures specifically for resistance management. In a disrupted system exclusively dependent on broad-spectrum insecticides (1991–1995), 75% ± 5% of cotton area was sprayed with mixtures of these materials. With the availability of selective insecticides, few broad-spectrum products are used today and mixtures of insecticides are sprayed on only 36% ± 3% of the cotton area (2015–2020). CONCLUSION: Although mixing has theoretical relevance, it is diminishing in stable systems with diverse modes of action and adherence to moderation principles. Arizona cotton guidance prioritizes multi-crop refuges over mixtures for resistance management. Integrated research and education, targeting professional pest managers, are pivotal in advancing resistance management without mixtures specifically designed to prevent or mitigate resistance.