الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
 |  | from | 133 |  |  |
| | | from | 133 | | |
Abstract
A multifaceted approach is required for weed management, made upon basic understanding of weeds and the crop. Weed management may encompass either chemical methods (herbicides), nonchemical methods (bioherbicides) or a blend of the two. Chemical weed measures include use of herbicides which provide a means to suppress or even eliminate standing weeds. Cultural measures include physical and ecological management practices that can be employed to eliminate the need for herbicide control. Mechanical control comprises of various methods like mowing, pulling and digging. Biological control employs the use of various living agents to suppress vigor and spread of weeds although the best practice includes integrated weed management (Sharma and Gauttam, 2014).
Conventionally, a weed is distinctly defined as any plant growing where it is not required. This definition can relate to crops, native plants as well as non-native species. If it is measured to be a nuisance where it is increasing, it can be termed a weed. However, weeds are not just unnecessary species; they can have substantial negative and rarely positive impacts when they are there. Weeds can effectively compete with crop species; can lower yields, increase labor requirements and ultimately increase food costs for the consumer (Klingman and Ashton, 1975). A plant is often termed a ”weed” when it has one or more of the following characteristics like little or no value (as in medicinal, material, nutritional or energy), rapid growth and/or ease of germination and competitive with crops for space, light, water and nutrients.
Weed control is the botanical component of pest control, which attempts to stop weeds from challenging with domesticated plants and livestock. Several strategies have been developed in order to contain these plants (Ambach et al., 1982). Weed represent about 0.1% of the world flora and in agro-ecosystems, weeds and crops have co-evolved together right from the prehistoric times as revealed by pollen analysis studies. Numerous methods of control have been developed, all of which are still used today. Though integrated weed management practices were developed and practiced which will ultimately offer effective weed control through chemical as well as mechanical, biological and cultural methods. The original strategy was manual removal including ploughing, which can cut the roots of weeds. More recent approaches include herbicides (chemical weed killers) and natural or bioherbicides (biological weed killers) (Parker and Riches, 1993).
Weeds are known to cause enormous losses for a large number of field crop species due to their interference in agroecosystems (Mohler, 2001). Weeds have a significant economic impact on agricultural production (Buhler, 1999) as evidenced by the efforts spent on their management. In 2002, global herbicide sales were nearly US $ 28 billion, constituting 47 percent of the total agrochemicals used worldwide (Agrow, 2003). Indeed, three million tons of herbicides per year are used in most agricultural systems (Stephenson, 2000; Chung et al., 2003).
The loss of crop yields due to weed is enormous. Lacey (1985) reported that sometimes weeds cause even 100 percent of crop loss. Although a number of weeds.