illustrative list of weeds (Naidu, 2012)8 that are used in traditional systems of medicine has been provided in Table 1. While the Naidu8 was consulted during preparation of the illustrative list, their habitat categorization was allotted by authors own survey of agricultural fields in different geographical locations over several years. The list includes some important weeds found both in the dry land as well as wet land in agriculture farms (Figure 1 and 2); however, fallow lands, road side lands, etc., do harbor variety of weeds. Their habitat ranges from alpine zone to arid zones.

Implications of weed control and their management

With increased awareness of environmental pollution focus is now shifting to adapt ecofriendly weed management practices. The composition and competition of weeds are dynamic which mostly depends on the type of soil, climate, cropping system and management factors. For example, competition for Andrographis paniculata, varies from agricultural land to fallow land to roadside habitat. To control weeds, in many rural agricultural fields weeding is carried out manually employing manual labor. An alternative to hand weeding is mechanical weeding and chemical weeding. In paddy fields, weeding is carried out just before application of fertilizers to avoid competition and prevent robust growth of weeds. The major constraint in hand weeding is labor shortage and cost. Thus, poor farmers employ their own family members to hand weed. However, for larger farms this is practically impossible. In some areas, deep ploughing and crop rotation is followed. Mucuna is used as a cover crop in suppressing weeds, especially spear grass9. However, this practice has its own disadvantage. Some of techniques further include frequent checking of potential weeds when they are establishing in the soil and removal before they are spread. Composting, ensiling, or feeding weeds to live-stock can destroy weeds to certain extent. Some mechanical techniques such as hand-pulling, hoeing, mowing, plowing and digging are also practices. Chemical weed control is considered one of the best methods to control weeds, but is associated with cost and environmental pollution. Uneducated or ill-informed farmers do not consider side effects on humans, animal and environment that would result from a prolonged and multiple uses of chemical weedicides. They have severe impact on animals, fish growing in nearby water bodies, persistence in soil, toxic residues in food, vegetables, fodder and even human beings. Some weeds have bioremediation activity and take up residual chemicals into their system. One typical example is presence of toxic and pesticide residues in herbal extracts of Bacopa monnieri. It is observed that in spite of best agronomy practices plant tend to accumulate toxic residues in the foliage. The explanation is simple. B. monnierie is weed in wetlands of rice fields. All the pesticide and herbicide residues present in the soil are taken up B. monnieri.