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

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.