The term ‘weed’ is usually refers to plants occurring in situations where they are unwanted. There is no botanical or taxonomic category of weeds, although there is a clear definition of invasive plants.
The definition of weed adopted by the European Weed Science Society is ‘any plant or vegetation, excluding fungi, interfering with the objective or requirements of people’.
The abundance of weeds is often of more concern than the mere presence of them. Farmers and land managers are usually less concerned about the occurrence of a few isolated plants in a field, even noxious ones, than the ocucp0aiton of land by vast numbers of weeds.
In agroecosystem weeds can reduce crop yields and quality, interfere with harvesting operations, reduce utility and value of land for raising livestock or other production uses, and pose threats to livestock through toxicity, indigestibility, and low nutritional content, as well as by well as by having spines, thorns or other detrimental physical features.
One of the characters of weed is rapid seedling growth and the ability to reproduce when young. For example, redroot pigweed can flower and produce seed when less than 8 in. tall.
Roots of some weeds are able to penetrate and merge from deep in soil. Their roots and rhizomes are capable of growing many feet per year.
What is weed in agriculture?
