Herbicides, Plant Resistance to Herbicides

A growing number of weed species have evolved resistance to certain herbicides around the world, but the total area infested with resistant weed populations is still relatively small. Resistance to some herbicides occurs at a relatively high frequency within many weed populations, and continuous use of these herbicides will select for those variants. Herbicide resistance deriving from target site mutations has occurred rapidly to those herbicides that share most or all of the following characteristics: 1) a single site of action, 2) a high persistence in the environment, 3) a high level of efficacy in causing plant death, 4) a high rate of mutation of the active site, and 5) a less debilitating effect by alteration of this herbicidal site. The development of weed resistance based on other mechanisms of resistance, such as herbicide compartmentation or metabolism, is more difficult to predict, because in many cases the cellular factors involved in herbicide movement or sequestration are less well-characterized than are those related to the site of action. The development of multiple-resistance mechanisms is of particular concern, because fewer new herbicides are released and many of the new herbicides have sites of action or mechanisms of metabolism in common with older herbicides, to which resistance has already developed. Combining herbicides with other herbicides either in mixtures or in rotations will greatly extend the usefulness of herbicides for the farmer. Keywords: herbicide resistance; herbicide tolerance; multiple resistance; cross resistance; mechanisms of resistance; herbicide mode of action; herbicide site of action; herbicide metabolism; herbicide selectivity; photosynthesis-inhibiting herbicides; membrane disrupters; ALS (acetolactate synthase)-inhibiting herbicides; glyphosate; ACCase (acetyl-CoA carboxylase)-inhibiting herbicides; mitotic disrupters; auxinic herbicides; management of herbicide-resistant weeds