Weeds and Their Control
There are 3 serious pests of the crop plants which causes loss of yield, i.e.
1. Insect-pests,
2. Diseases,
3. Weeds.
The estimated losses in crop yields range from 5% in clean cultivated fields over 70% in neglected fields depending upon the degree of weed infestation. They compete with crop plants for nutrients, water, light and space. The loss of ‘N’ through weed is as high as 150 kg/ha.
WEED: Any plant not sown in the field by farmer is out of place, called weed.
The term, ‘weed’ used by Jethro Tull for the first time, suggested an useless and harmful plant that persistently grows where it is quite unwanted.
According to Robinson: Weeds are that species of plants which grow unwanted or are not useful, often prolific, persistent, interfere with agricultural operations, increase labour cost and reduce the crop yields.
Weed is a plant growing where it is not wanted, unwanted plant, out of place, extremely noxious, useless, and poisonous.
Characteristics of weeds: Weeds are like any other crops plants in size, form, morphological & physiological characters but possess the following characteristics, on account of which they are considered as enemy of crops by the farmer.
1. The weed seeds germinate early and the seedlings grow faster. They being hardy, compete for light, moisture and nutrients.
2. They flower earlier, run to seed in profusion and mature ahead of the crop. They are difficult to control and it may be even impossible to eradicate some weeds completely.
3. They are non-useful, unwanted & undesirable.
4. They are harmful to crops, cattle and human beings.
5. They can thrive even under adverse conditions of soil, climate, etc.
6. They are prolific and have a very high reproduction capacity. E.g.: A plant of satyanashi (Argemone mexicana) produces over 5000 seeds while a plant of striga produces over half a million seeds.
7. Viability of weed seeds remains intact, even if they are buried deep in the soil. In some cases, the seeds may remain viable even after passing through the digestive tract of the animals.
8. The seeds may have special structures like wings, spines, hooks, sticky hair, etc. on account of which they can be easily disseminated over long distances.
9. Many weeds like Cynodon dactyl on are vegetatively propagated and spread rapidly all over the field even under adverse conditions.