Biotechnology provided new dimensions to herbicide technology. Transgene technology has generated herbicide-resistant crops (HRCs) that have profound impact on the herbicide market. This same technology has the significant potential to make crops better competitors with weeds through improving competitive traits or making the crop more allelopathic. Living biocontrol agents can sometimes be applied to weeds, much like a herbicide. In the bioherbicide approach, microbial plant pathogens are applied to target weeds. Fungi, bacteria and viruses offer great promise as bioherbicides. Formulations of Phytophthora palmivora (De Vine) as a selective mycoherbicide for the control of milkweed ( Morrenia odorata ) in citrus, and Colletotrichum gloeosporioides (Collego) for the control of Northern joint vetch in rice and soybean, are now widely used in developed countries. Extensive research has demonstrated that several allelochemicals possess good herbicidal activity. Thus, A crop that is genetically engineered to be resistant to yet another selective herbicide must fulfil a weed management need that is unmet, such as those niches that were filled by bromoxynil-resistant crops.