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Harmful Plants: Mealy bug h the appearance of absorbent cotton, in little patch in the axils of leaves and on the underside leaves close to the midrib. The presence of n spider is revealed by small silvery patches on tl leaves. The ladybug is a destroyer of insec that are harmful plants to plants. A gardener can gii mass treatment by strongly fumigating his greei house with a deadly insecticide, but the amatei grower of house plants has to use insecticidi more carefully. He can prepare an outside bo with a glass top and use this as a fumigator, c he may discard insecticides and wash his planl with strong soap lather, then wash clean afte fifteen minutes.
In agriculture a pest is any organism that damages or destroys plants useful to man and the term is taken to apply to harmful plants insects, mammals and birds. Crops also suffer from micro-organisms that cause disease and competing wild plants or weeds.
The important groups of pesticides are insecticides, fungicides and nematicides - for the eelworms which are microscopic nematodes feeding on plant roots. Herbicides are chemicals used for weed control. In tropical and subtropical areas of the world it is the insecticides that tend to be more important. But in the USA (which uses as much agricultural chemicals as the rest of the world together) herbicides are more widely applied than pesticides.
Because inhibition of reproduction and development was possible in natural insect populations, a new generation of insecticides derived from insect hormones might be developed. Unlike DOT, which attacks useful and harmful plants insects indiscriminately, became a hazardous component of the general environment, and to which many harmful plants insects became completely resistant, insect hormones could be highly specific, act only at certain stages in the life cycle, and conceivably could be "resistant-proof" for many decades. To what degree such pesticides would enter the total environment and what the effects might be on other organisms remained to be established. |
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