Đang chuẩn bị liên kết để tải về tài liệu:
Fruit growing in the tropics - Part 8

8 Crop protection Crop protection practices are linked to the cropping system. The use of commercial pesticides is by and large limited to orchards and large plantations. In orchards of small trees, such as mandarin, guava or apple, pesticides are often used to excess. Intensive crop care drives up the cost so much that the grower cannot risk crop failure; | 8 Crop protection Crop protection practices are linked to the cropping system. The use of commercial pesticides is by and large limited to orchards and large plantations. In orchards of small trees such as mandarin guava or apple pesticides are often used to excess. Intensive crop care drives up the cost so much that the grower cannot risk crop failure he tries to protect his trees with whatever pesticide is recommended and available . Routine spraying without regard for the level of infestation is common. In this way the natural checks and balances between pests and their predators in the orchard are disturbed so that one treatment breeds the need for the next one. Moreover there are serious health risks for the grower who handles the materials and is exposed to the spray drift for the consumers when they eat the fruit and for the creatures living in the soil and nearby water courses that become polluted. Tall trees cannot be treated with small knapsack sprayers and even spraying of medium-sized trees in orchards e.g. rambutan in Thailand mango in the Philippines is the exception rather than the rule. If the orchard consists of a mixture of fruit crops it is hard to avoid pesticide drifting onto non-target trees. The scattered trees in home gardens backyards along field borders and watercourses do not lend themselves to being sprayed with pesticides. Several traditional crop protection measures are practiced in home gardens but mainly on small plants and in nursery work e.g. use of wood ash and plant extracts . On the trunks of tall trees in the garden one often sees collars made of metal sheeting or thorny branches to stop rodents from climbing the trees. Large fruit such as jackfruit may be bagged to protect it against insects birds and bats. Smaller fruit e.g. guava is sometimes bagged too in particular to prevent fruit flies from laying their eggs there. On the whole home gardeners hope that the rich mixture of plants will make it more difficult for pests or .