Elsevier

Crop Protection

Volume 145, July 2021, 105614
Crop Protection

Cotton row spacing for boll weevil management in low-input production systems

https://doi.org/10.1016/j.cropro.2021.105614Get rights and content

Highlights

  • Boll weevil management can benefit from cultural control practices such as row spacing.

  • Row spacing of 0.5 m increases reproductive structures infestation and abcision.

  • 0.75 m and 1.0 m row spacings help on boll weevil management without altering yield.

  • Wider row spacings (0.75 m and 1 m) produced better quality lint.

  • Wider row spacings (0.75 m and 1 m) should be preferred over narrow row spacings (0.5 m).

Abstract

Despite being an important commodity, < 2% of the cotton cultivated area in Brazil is considered to be “low-input”. A major reason for this relatively small area is infestation by boll weevils (BWs), Anthonomus grandis grandis Boheman, which are usually controlled using conventional synthetic-based insecticides. Cotton grown in low-input systems of Brazil lack an integrated pest management strategy. We hypothesized that the alteration in row spacing would act as a preventive cultural practice driving BW infestation down while improving lint production and fiber quality, thus justifying its adoption. We assessed the effects of three row spacings: 0.5 m (narrow), 0.75 m (conventional), and 1.0 m (wide) on boll weevil infestation levels, during two seasons in areas without the adoption of any control against BW. In both seasons, plants were surveyed for 23 successive weeks and shed structures were collected for 17-21 weeks. BW-infested and non-infested reproductive structures, number of BW, and yield parameters were assessed. Shed structures were kept for 21 days to assess BW emergence. The narrow row spacing was the least effective, and the conventional and wide spacings delayed boll weevil control interventions and resulted in fewer boll weevil-injured reproductive structures early in the season, and produced lower numbers of adult boll weevils without altering the quantity and improving the quality of lint and the financial returns obtained from a better quality lint. This is the first study to demonstrate the effect of row spacing on boll weevil infestations and inflicted injury in low-input systems. The results can also be applied to conventional cotton production systems.

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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