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.
Inhibition of enzymes in shikimic acid pathway leads to depletion of the aromatic amino acids tryptophan, tyrosine, and phenylalanine. Symptoms include yellowing of new growth and death of treated plants in days to weeks. Sublethal doses on annuals may result in limited chlorosis and malformed shoot tissue. Regrowth of woody or creeping perennial species may show shoot malformation as well. Glyphosate is limited to foliar applications only.