Immediate bending and twisting of leaves and stems are an auxin response. Surviving plants produce malformed new shoot growth, root development on dicot stems, malformation of roots, and cell division resulting in undifferentiated lumps. 2,4-D tends to be weak on smartweeds, legumes, chickweeds and bur cucumber. Soil activity is sufficient to use for preemergence applications in corn. High doses under evergreen shrubs can cause injury to them.
Soybeans are particularly sensitive to dicamba.
The diflufenzopyr doubles the activity of dicamba by preventing the movement of dicamba out of cells in the shoot meristems thus increasing the amount of herbicide present. Since picloram is highly persistent and very mobile, care must be taken to prevent contamination of ground water. These compounds are often mixed to provide control of a broad spectrum of broadleaf weeds. Injury to off-target broadleaf vegetation is a major problem with auxin growth regulators, since auxin responses are observed at doses considerably lower than those required for effective control of weeds. Excessive doses injure and plug the phloem so that translocation is slowed or stopped.