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Title: Proactive spraying against boll weevils (Coleoptera: Curculionidae) reduces insecticide applications and increases cotton yield and economic return

item Showler, Allan

Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/9/2005
Publication Date: 12/15/2005
Citation: Showler, A., Robinson, J.R. 2005. Proactive spraying against boll weevils (Coleoptera: Curculionidae) reduces insecticide applications and increases cotton yield and economic return. Journal of Economic Entomology. 98(6):1977-1983.

Interpretive Summary: Current management of boll weevils in cotton in the Lower Rio Grande Valley can require nine or more insecticide applications per growing season. The current management is comprised of early insecticide applications when cotton fruit are small, and additional applications that are based on the percentage of infested fruit. A new approach has been developed for timing insecticide applications based on the most critical crop stage for boll weevil reproduction and for vulnerability to weevil-induced crop loss. The new approach for insecticide applications to reduce boll weevil populations resulted in increased cotton fiber production, fewer insecticide applications, and greater profit than the untreated control and the standard insecticide approach. These results will lead to improved yield and profit of cotton production, and reduced environmental risk of chemical pesticide use.

Technical Abstract: The current standard practice of pre-emptive insecticide applications at the start of pinhead (1-2 mm-diameter) squaring, followed by threshold-triggered (when 10% of randomly selected squares have oviposition punctures) insecticide applications for boll weevil, Anthonomus grandis grandis Boheman, control does not provide a reliably positive impact on cotton, Gossypium hirsutum L., yields in the Lower Rio Grande Valley of Texas. This study demonstrated that the 4-6 fewer applications used in a "proactive" approach, where insecticide treatments began at the start of large (5-8 mm-diameter) square development and continued at 7-8 d intervals for as long as large squares were predominant, resulted in fewer oviposition-punctured squares, than the standard treatment. Although boll populations were not statiscally greater in the proactive treatment than in the standard treatment, and populations of beat bucket-collected adults were lower in the proactive treatment than in the other treatments at only one of the two experimental locations, lint yield was 46.4% and 56.2% greater in the proactive treatment than the standard treatment at the KSARC and Ansul experimental locations, respectively. The combination of fewer insecticide interventions and increased yield made the proactive approach 115-130% more profitable than the standard spray regime when all applications were made by tractor-mounted spray rig, and economic returns were increased further if some standard applications had been made by aircraft. Mechanisms that explain how the proactive approach protects the cotton crop at its most vulnerable stage, and when the crop most contributes toward accelerated boll weevil population build-ups, are discussed.