Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 15, 2008
Publication Date: October 15, 2008
Citation: Showler, A.T., Robinson, J.R. 2008. Cotton harvest at 40% versus 75% boll-splitting on yield and economic return under standard and proactive boll weevil (Coleoptera: Curculionidae) spray regimes. Journal of Economic Entomology. 101(5):1600-1605.
Interpretive Summary: The standard practice of pre-emptive and threshold-triggered spraying for boll weevils in cotton does not provide reliable protection of cotton lint production. We examined levels of boll weevil infestation and yield in conventionally and proactively sprayed field plots that were either harvested at the standard 75% hull-split or earlier, at 40% hull-split. Economic returns were greatest in the proactively-sprayed plots harvested at 75% hull-split because of improved protection of large squares and elimination of late-season sprays, but harvesting at 40% hull-split was more economical than harvesting at 75% hull-split because late-season sprays and irrigation did not occur in that treatment.
The standard practice of two or three 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 reliable protection of cotton, Gossypium hirsutum L., lint production. This study showed that 3–6 fewer spray applications in a “proactive” approach, where spraying began at the start of large (5.5–8-mm-diameter) square formation and continued at ~7-d intervals while large squares were abundant, resulted in fewer infested squares and 1.4- to 1.7-fold more lint than the standard treatment during 2004 and 2005. The combination of fewer sprays and increased yield made the proactive approach more profitable than the standard approach which, in contrast, provided negative or low economic returns. Harvest timing at 40% boll-split was better than at 75% boll-split in the standard spray regime because of the cost of an extra irrigation and additional sprays associated with the 75% boll-split harvest timing. In contrast, harvest at 75% boll-split in the proactive spray regime resulted in greater economic returns than cotton harvested at 40% boll-split because of improved protection of large squares and the elimination of late-season sprays inherent to standard spray regime. Because proaction and harvest timing are based on an important relationship between nutrition, boll weevil reproduction, and economic inputs, the tactic of combining proaction with harvest at 75% boll-split will probably be applicable where boll weevils are problematic regardless of climate or region.