Generally, small weeds are more susceptible to herbicides than large weeds but small crop plants also may be more susceptible. Herbicide rate reduction may be possible if the herbicide is applied to weeds that are smaller than the weed size on the herbicide label. The crop also may be smaller than the suggested crop stage at application so knowledge of safety to the crop would be needed. So, herbicide rates can sometimes be reduced by early application but special knowledge is needed. Companies can not write a label that anticipates all environments in which a herbicide may be used.
Environment has a large influence on the efficacy of herbicides.
So, herbicide rate reduction may be possible if the specific environment will favor high phytotoxicity from the herbicide but special knowledge is needed on the environment-herbicide interaction. The efficacy of some postemergence herbicides is enhanced by adjuvants such as surfactants, crop oils, methylated seed oils or fertilizer. Adjuvants vary considerably in ability to enhance herbicide efficacy even among a class of adjuvants. For example, some surfactants may double percent weed control from a herbicide while other surfactants may have little effect. The number of adjuvants presently sold is so large that testing all adjuvants with all herbicides is not possible.