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Incidence of Herbicide Resistance in Rigid Ryegrass (Lolium rigidum) across Southeastern Australia

Cases of herbicide-resistant weeds worldwide are continually compiled online in the International Survey of Herbicide Resistant Weeds (see website link on this page). Such weed biotypes are becoming increasingly common since the first reports of their occurrence in the 1950s. These biotypes survive herbicide application at doses that usually give effective control of the species. Resistant weed biotypes are a consequence of basic evolutionary processes. Individuals within a species that are best adapted to a particular practice are selected for and will increase in the population. Once a weed population is exposed to a herbicide to which one or more plants are naturally resistant, the herbicide kills susceptible individuals, but allows resistant individuals to survive and reproduce. With repeated herbicide use, resistant weeds that initially appear as isolated plants or patches in a field can quickly spread to dominate the population and the soil seed bank.

The Weed Science Society of America supports research, education, and extension efforts in all facets of herbicide resistance, including characterizing new cases of resistance, discovering the mechanisms and modes of inheritance of resistance, and identifying best management practices for preventing, delaying or managing herbicide resistance in weeds.