Cotton row spacing for boll weevil management in low-input production systems
Graphical abstract
Introduction
Cotton (Gossypium hirsutum L. Malvaceae) is produced globally on ≈34 million ha. Areas dedicated to organic systems occupy ~2% of the total cultivated area, particularly in India, China, Kyrgyzstan, Turkey, Tajikistan, and the United States (Organic Trade Association, 2019). Low-input cotton production areas in Brazil are mostly in semi-arid northeastern Brazil, where ≈23.3% of the total cotton production area occurs, of which 0.04% is organic (Organic Trade Association, 2019). The mid-west part of Brazil also cultivates some low-input cotton (Amipa, 2020) and have potential to expand cultivation to use cotton as a rotation crop with horticulture crops organically grown in many of these areas (Codeplan, 2018).
The boll weevil, Anthonomus grandis grandis Boheman (Coleoptera: Curculionidae), occurs from northern Argentina to the southern United States (CABI, 2019), and it is a limiting factor to Brazilian cotton production. Larval and adult boll weevils feed and females lay eggs on the reproductive structures of cotton, concentrating their attack on large buds (5.5–8.0 mm diam), although feeding and oviposition activities also occur on bolls, and feeding is noticed in seedling and mature cotton leaves, and petioles (Showler, 2007). Boll weevil attack on bolls negatively alters cotton lint quality and quantity (Showler, 2006). In temperate areas, boll weevil populations are typically diminished during winter (Showler, 2007) because of low temperatures and lack of food. In tropical and subtropical areas, however, the pest can be active year-round (Neves et al., 2014) because they can survive, albeit without reproducing, on alternative, noncotton food sources (Ribeiro et al., 2010). Immature boll weevil development inside cotton fruiting structures is protected from the action of insecticides (Neves et al., 2014). In conventional systems, frequent insecticide applications (19–25 per growing season) do not always hold injury below economically acceptable levels (Abrapa, 2015).
Adjusting cotton row spacing is a cultural practice that might be useful for managing boll weevil populations. Buds that were used for oviposition are shed by the plants within a few days (Showler and Cantú, 2005) and remain on the ground until larval and pupal stages develop into adults (Showler and Scott, 2005). Shed buds are subject to desiccation (Showler and Scott, 2005), and this can be influenced by row spacing (Pierce et al., 2001). Plant growth is also influenced by row spacing, especially in terms of numbers of reproductive branches (Silva et al., 2006). Further, plants growing on narrow row spacing can interfere with coverage by insecticide sprays (Hutchins and Pitre, 1984). Previous studies of row spacing have addressed either the pest (Pierce et al., 2001) or the crop (Silva et al., 2006, 2011) without considering both in concert, and those studies were limited to conventional systems. The purpose of this study was to investigate the influence of row spacing on boll weevil infestation and cotton fiber yield in terms of quantity and quality in a low-input cotton production system.
Section snippets
Experimental conditions
The study was conducted during two growing seasons, Jan–Aug 2014 and Jan–Oct 2017, at the University of Brasilia Experiment Station, 15.98 and 47.97 latitude and longitude, respectively. The experimental area is considered to be low-input because it has been cultivated under organic production system since 2009. Sprinkler irrigation was applied when rain did not occur for three consecutive days during critical developmental stages (seedling, flowering, and boll initiation). Mechanical soil
Boll weevil infestation and population
Accounting for the percentages of damaged fruiting structures, the decision to control boll weevils would have occurred upon reaching the economic threshold (10% of attacked reproductive structures) at 84 DAP for the 0.5 m (Fig. 1A) and 1 m (Fig. 1B) row spacings. Intervention against boll weevils would not be needed until 90 DAP in the 0.75 m row spacing treatment (Fig. 1C) in the first season. Also, on the last sampling date at 212 DAP, the percentage of damaged reproductive structures
Discussion
Data on boll weevil infestation during plant samplings allow us to observe that the delays in boll weevil control intervention, as well as the reductions in the number of times that boll weevils reached the economic threshold in the 0.75 m and 1 m row spacing treatments, appear to have resulted from lower boll weevil populations, diminishing production costs, and increasing financial returns by reducing discounts applied to the price paid for the yield, because of better lint quality. In
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
To the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) for the scholarship and to the Conselho Nacional de Pesquisa e Desenvolvimento Tecnológico (CNPq) for the scholarships and fellowships.
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