ABSTRACT
Plant species have at least four different mechanisms which affect herbicide selectivity. These result in differences in the absorption, translocation, rate of metabolism, and sensitivity of the site of action to the herbicide. The primary mechanisms of natural selectivity to the imidazolinones include the first three, with differential metabolism playing the predominant role. This chapter summarizes present knowledge about the mechanisms of selectivity for imazamethabenz-methyl, imazapyr, imazaquin, and imazethapyr. Imazamethabenz-methyl is selective on cereals and sunflower. This herbicide is composed of two positional isomers and differs from the other imidazolinones in that it is applied as an ester rather than as a salt of the acid. Imazapyr controls a broad spectrum of annual and perennial dicot and monocot weeds and is particularly effective on woody perennials. However, certain species in the conifer, composite, legume, and euphorb families have very high tolerances to imazapyr.
