Differentials in plant height can provide selectivity by using directed sprays or wipe-on devices. Differential retention and wetting can account for selectivity between plants with markedly different leaf orientation and surface wax. Adjuvants added to foliar sprays can alter this type of selectivity. Differences in rates of herbicide penetration, translocation, or deactivation may account for selectivity. In some cases, differential metabolism from an inactive to an active compound accounts for selectivity.
Differential metabolism is the most common mechanism of selectivity with modern herbicides.
Individuals within a species can exhibit a wide range of heritable differences to herbicides. Sugarbeets, corn, soybeans, johnsongrass, and Canada thistle are all species in which individuals can exhibit up to a 5-10 fold difference in herbicide response. Additive, antagonism and synergism are terms used to describe the amount of activity in relation to the expected response. Herbicides such as haloxyfop and fluazifop can exhibit reduced activity when tank mixed with phenoxy herbicides, acifluorfen, and bentazon. Dimension is dicamba with an added compound which about doubles the activity.