Physiology & Metabolism of Dicamba

Mode of Action & Lethality

The mode of action of dicamba is probably similar to that of the phenoxy carboxylic acids. Rapid, abnormal, cell growth then leads to the disruption of the phloem system and normal auxin balance in the plant. As with the phenoxy carboxylic acids, these herbicides act by stimulating abnormal cell growth in meristematic cells. This can result in the blockage of phloem vascular tissue. Extensive destruction of cambial, phloem cells near meristems occurs within days of treatment. The plant is killed by starvation resulting form an inability to translocate needed energy in the phloem.

Uptake and Movement of Dicamba in Plants

Dicamba is rapidly absorbed by plant root and shoot tissue. Dicamba translocates readily in the xylem and phloem. Dicamba taken up by plant roots is translocated mostly in the xylem initially, but over a longer time it moves to areas of high metabolic activity.

Basis of Selective Toxic Action between Susceptible & Resistant Species

Selective dicamba toxicity amongst plant species appears to be a function of uptake, distribution in the plant, and metabolism. In some tolerant species, translocation is limited to the xylem. Tolerant species metabolically degrade dicamba rapidly. The primary degradation pathway is by metabolism of the herbicide (ring hydroxylation followed by very rapid glucoside conjugation).　

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