Weed management in cotton (Gossypium hirsutum L.) through weed-crop competition: a review

The agriculture sector is embracing energy efficient conservation systems and technological innovations to meet the ever increasing demand for food, fibre, and fuel in tune with the rapidly increasing human population. The genetic modification of plants is one of the technological innovations that is adopted rapidly across the world. In cotton, many major producing countries have adopted herbicide-tolerant genetically modified crops. Over-reliance on herbicides for weed management in both genetically modified and conventional systems has led to the rapid evolution of herbicide-resistant weeds. Poor weed management can cause up to 90% yield loss in cotton. Undoubtedly, integration of non-chemical methods and diversifying weed control options would ensure the sustainability of available weed management options, including herbicides. Increasing crop competitiveness is one of the approaches that could be integrated with the current weed management systems. Choosing cultivars with early vigour, use of narrow row planting, orienting crop rows with regard to sunlight, and adjusting planting density are some of the approaches that could enhance the competitiveness of crops over weeds. Review of the available literature on cotton indicates weed suppressive benefits by enhancing crop competitiveness through increasing planting density and narrow row spacing. Early canopy closure in narrow row spaced systems would suppress many problem weeds. In addition, herbicide efficacy may be increased due to competition offered by a dense crop stand, which may reduce herbicide selection pressure on weeds. However, the use of narrow row spacing is still in an infant stage in many cotton-growing countries and the success may depend on the environment, soil type, and resource availability. This review analyses and reports the potential benefits of increasing crop competition as a weed management option and also highlights research to be undertaken to ensure the adoption of different strategies on a much wider scale