2 4 d amine salt 720g/l SL is a group code O herbicide.  Any weed population may contain individuals naturally resistant to 2 4 d amine salt 720g/l SL  and  any other group code O herbicides.  The resistant individuals can eventually dominate the weed population if these herbicides are used repeatedly.  These resistant weeds may not be controlled by  or  any other group code O herbicide.