Herbicide resistance will continue to be a weed management problem as long as herbicides are used for weed control. Repeated use of a herbicide increases the risk that a resistant biotype will be selected. The major mechanisms for resistance are either a change in the herbicide's target-site or increased herbicide metabolism. A population can evolve to be resistant to more than one chemical family of herbicides and may contain more than one mechanism for resistance. Inheritance of herbicide resistance has not been determined in many cases; however, in most cases where it has been determined, a single dominant or semi-dominant nuclear gene is most often responsible.