Weeds and Their Management: Rationale and Approaches
Defining weeds is perhaps one of the most complex and intriguing problems in plant science. A number of definitions and views have been put forward, but none have met with universal satisfaction. Etymologically, a weed means a plant growing at a place where not required and/or interfering with growth of cultivated plants. Scientists have tried to define weeds in anthropomorphic, biological, and ecological terms. Such eminent botanists as Harper (1960) and Salisbury (1961) defined weeds as nuisances or plants growing where not required. Harlan and deWet (1965), King (1966), and Zimdahl (1999) have attempted to compile various definitions of the weed. Most of the definitions, however, suggest that these are objectionable unwanted plants interfering with the activity of humans and cultivated plants. Many ecologists have also tried to define weeds from different perspectives. Bunting (1960) defined weeds as pioneers of secondary succession, and weeds in an arable field is a special case. Pritchard (1960) referred to weeds as opportunistic species that follow human disturbance from the habitat. Rejmánek (1995) opined that the terms weeds, invaders, and colonizers are often overlapping and may be considered as one. Begon, Harper, and Townsend (1996) described weeds as successful predators arising out of a mismatch between habitat and types of growing plant. According to Crawley (1997) a weed is a problem plant whose abundance is more than the specific level. However, the specific level remains to be determined and varies from one place to another. Mohler (2001) defined weeds ecologically as the plants that are most successful in colonizing disturbed but potentially productive sites and are able to maintain their abundance even under repeated disturbed conditions.