TROPICAL AND SUB-TROPICAL TREE AND BUSH CROPS

A number of tree and bush crops, especially those grown on plantations have been treated with pesticides to avoid major crop losses. In the absence of fungicides, coffee was abandoned in Sri Lanka in the 19th Century due to devastating infestations of leaf rust (Hemileia vastatrix) and replaced by tea, although in South East Asia cultivars of coffee resistant to the rust are now grown. Weed management has been using postemergence herbicides to maintain pathways for harvesting, especially in oil palm and rubber estates. Apart from spraying coffee for leaf rust control, other examples of fungicide spraying include bananas for Sigatoka disease (Mycosphaerella musicola) control, cocoa for black pod (Phytophthora palmivora) and rubber to control the South American leaf blight (Microcylus ulei). Biological control of insect pests is more important on perennial crops and natural enemies need to be conserved, so selection and use of insecticides needs to be very judicious. Unfortunately, some insecticides have been used with disastrous results by exacerbating other insect pest problems, for example insecticides applied to citrus, mangoes, olives and other crops often increase the damage due to scale insects. The investment in crop protection is often a fixed cost, but as the income may fluctuate due to the yields attained and world prices, the proportional cost of using pesticides can vary, so every effort is needed to optimise their use and minimise costs…