Weed resistance challenges and management under herbicide resistant cropping systems

Over the last six decades, herbicides have been the mainstay of weed management in cropping systems around the world, especially in the Western Hemisphere. A direct consequence of intensive use of herbicides is the development of resistance in weed populations. The extreme popularity of transgenic glyphosate-resistant crops has resulted in resurgence in herbicide resistance issues and further aggravated the situation. The major factors affecting evolution of herbicide resistance in weeds include gene mutation, initial frequency of resistance alleles, inheritance, weed fitness in the presence and absence of herbicide, type of pollination, gene flow, and farming practices that favour a limited number of dominant weed species. As of now, five modes of herbicide resistance have been identified in weeds: target-site mutation, metabolic deactivation, reduced absorption and/or translocation, sequestration, and gene amplification. Integrated and diversified management programs are indispensable in combating herbicide resistance in weed populations.