Many plants can deactivate or metabolize a herbicide before plant injury occurs.
Wheat and barley tolerate growth regulator herbicides, such as 2,4-D and MCPA, because they can metabolize these herbicides faster than broadleaf plants. The genetics of a plant also affect a plant's tolerance to a herbicide. This difference is due to specific genes within the plants. Many plant-related factors determine herbicide selectivity. Plant age and height differences between crops and weeds can be used successfully to kill some weeds.