Occurrence and Mechanisms of Weed Resistance to Glyphosate

Glyphosate is a nonselective foliar-applied herbicide that has been used for over 20 years for the management of annual, perennial, and biennial herbaceous species of grasses, sedges, and broadleaf weeds, as well as woody brush and tree species (Bradshaw et al. 1997). Commercialization of engineered glyphosate resistance in several crop species has further expanded the in-crop use of the herbicide (Padgette et al. 1996). In addition to being highly effective on a broad spectrum of annual and perennial weed species common to many cropping systems, glyphosate has other favorable environmental characteristics such as strong sorption to soil and very low toxicity to mammals, birds, and fish (Padgette et al. 1996). These factors have contributed to glyphosate being the most widely used herbicide in the world (Powles et al. 1997).