A pest is any destructive organism which causes great economic loss by destroying crop plants or products obtained from them. Pest of crop plants include weeds, insects, mites, nematodes, rodents, fungi, bacteria, and viruses. Field crops are infested by a large number of insect pests and diseases. If these pests are not controlled at appropriate time they can damage the crops to the extent of 50 to 70 per cent.
There are various method by which insects and diseases can be controlled. One of the most common and effective methods is the use of pesticides or biocides which includes insecticides (for killing the insects), weedicides (for killing the weeds) and fungicides mites, rodents and fungi are called pesticides. These chemicals (pesticides) are sprayed on crop plants or used for treating seeds and soil. However, one should try to avoid the would be far better if we adopt the preventive measures rather than allowing the crops to be infested by pest and then control them by pesticides. Some of the preventive measure of pests are the following:
1. use of resistant varities of crop plants
2. selection of optimum time of sowing the crops.
3. crop rotatin and multiple cropping.
4. Clean cultivation.
5. Summer ploughing.
Humid and warm climate is regarded as more favourable for infestation of insect pest and diseases. That is why kharif crop are more prone to these pests in contrast to rabi crops like gram, sugarcane, pea, etc.
Weeds are unwanted plants in the cultivated fields. In other words, plants other than crops the weeds. Weeds tend to compete with the crops for food,space and light. In comparison of cultivated crops, the seeds of weeds, germinate easily,their seedling grow faster, they flower early, their seed production begins after a short growth period and they produce large number of seeds. In fact, weeds take up all the nutrients and reduce the growth of crop in various ways. Therefore, removal of weed plants from cultivated field in early stage of crop is essential to harvest high yield. In unirrigated condition weeds affect the water availability and in irrigated condition there is competition for nutrient uptake between weeds and crop plants. For example, barley or mustard plants act as weeds in a wheat field and compete with crop for nutrition. Likewise, wild sorghum grown in cultivated crop fields of sorghum acts as a weeds plant and compete with crop for water and nutrients.
Types of weeds:-
Infestation of weeds is more during kharif season than in rabi season. Based on the morphology of plants, weeds can be classified into narrow leaf weeds and broad-leaf weeds.
1. Some of the important weeds of kharif season are the following.
2. Nutgrass or mothaWild sorghum
3. Wild sorghum
II some of the important weeds of rabi season which infest wheat crop are the following.
Methods of weed control
They include the following methods proper bed preparation, timely sowing of crops, intercropping and crop rotation.
3. Chemical methods
Chemical weed killers called herbicides or weedicides, are sprayed on weeds to destroy the. This is called chemical control of weeds. Some common examples of weedicides are the following 1. 2,4 –D (2,4 –Dichlorophenoxy acetic acid).ii. Atrazine iii. Fluchloralin iv. Isoproturon.Biological control Biological control of weeds involves the deliberate use of insects or some other organisms which consume and specifically destroy the weed plants. The best Indian example of biological control is
4. Biological control Biological control of weeds involves the deliberate use of insects or some other organisms which consume and specifically destroy the weed plants. The best Indian example of biological control is eradication of prickly-pear cactus by using the cochineal insects in Maharashtra and Tamil Nadu. Generally, a combination of one or more of these weed control methods is employed to get good results.
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