Résumé

ABSTRACT: The term weed in its general sense is a subjective one, without any classification value, since a "weed" is not a weed when growing where it belongs or is wanted. Weeds generally share similar adaptations that give those advantages and allow them to proliferate in disturbed environments whose soil or natural vegetative cover has been damaged. Naturally occurring disturbed environments include dunes and other windswept areas with shifting soils, alluvial flood plains, river banks and deltas, and areas that are often burned. Since human agricultural practices often mimic these natural environments where the weedy species have evolved, weeds have adapted to grow and proliferate in human-disturbed areas such as agricultural fields, lawns, roadsides, and construction sites. The weedy nature of these species often gives them an advantage over more desirable crop species because they often grow quickly and reproduce quickly, have seeds that persist in the soil seed bank for many years, or have short life spans with multiple generations in the same growing season. Weed seeds germinate earlier; their seedlings grow faster; they flower earlier; and form seeds in profusion; and mature ahead of the crop they infest. Measures against weeds comprise mechanical (cultivation and moving), cultural or cropping, biological and chemical means. Each of these methods has certain merits and a prudent farmer can make use of one means or a combination of them to control weeds efficiently and economically. In Valsad district mainly wheat, rice, sugarcane, vegetables, fruits, etc. is cultivated crops and weed is a serious problem as they compete with neighboring crops or plants of economic importance and reduce their yield. A total of about 215 weed taxa growing in the different crop area under investigation have been listed of 48 families and of these 180 taxa belong to dicotyledons and 35 to monocotyledons. The dicot: monocot ratio is 4.8: 1.2, means the dicot weeds dominate the crops of the area.