Date of this Version
The development of herbicide resistant weeds is described along with strategies to prevent development. Herbicide resistance refers to plants within a weed species that, after repeated use of a herbicide, are no longer controlled by normal rates of that herbicide. Herbicide resistance often develops in fields that have been sprayed with herbicides with the same site of action for several years. Herbicide resistance is usually attributed to slight genetic differences between resistant and susceptible plants. These changes occur at a frequency of one plant in a million or even a billion. Herbicide resistance is not dependent on the environment or growth stage. Resistant plants will survive the herbicide treatment even under ideal environmental conditions. The best defense against herbicide resistance is to avoid continuous selection for herbicide-resistant weeds.