Case Study 2: Cotton pest control

Caterpillar of Helicoverpa armigera. Credit Insect Images

Caterpillar of Helicoverpa armigera. Credit Insect Images

Pest management accounts for 25% to 45% of the costs of growing cotton in developing countries. Cotton accounts for nearly 25% of insecticide use worldwide.[1] Cotton pests such as bollworm (Helicoverpa armigera) however can be controlled by biological control, planting pest resistant varieties, cultural control such as deep ploughing and low density planting, the use of pheromones and bio-insecticides and even hand removal. A variety of crops can be intercropped with cotton to help recruit beneficial arthropods and natural enemies.

Moths of the African bollworm prefer to lay eggs on crops such as pigeon pea, chickpea, maize, sorghum and sunflower, so these crops can be used as a distraction when planted in strips or around the field to reduce damage on cotton crops. The preference of bollworms to lay their eggs on maize means that it is often used as a ‘trap crop.’ This preference is so strong that in some cases cotton plots remained almost clear of eggs when surrounded by a few rows of maize.[2]

Some successful examples can also be found in Asia. On cotton farms in the Xinjiang province of Eastern China, alfalfa has been planted around the field margins of 70,000ha of land. By cutting the alfalfa several times a season, beneficial insects are encouraged to move into the cotton areas, significantly reducing the number of Aphis gossypii, a damaging cotton pest in the region.[3] Similarly in Eastern India, intercropping cotton with lucern, cowpea and groundnut enhanced natural enemy populations, but cotton yields and overall profit of the system varied depending upon which crop was used. For example, cotton performed the worst when intercropped with sorghum and performed the best when planted with groundnut and chilli, highlighting the need to manage trade-offs between integrated pest management (IPM) concerns and system productivity and profitability.[4]

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