Experiments were conducted in order to establish the mechanism by which the synergist MZH 2091 increases metribuzin activity on ivyleaf morningglory. Herbicide absorption and metabolism were compared for plants treated either with 14C-metribuzin alone or with 14C-metribuzin plus nonlabeled MZH 2091. The compounds were applied via the roots for 3 h and the absorption was determined. After the pulse treatment, the plants were grown for additional 0, 3, 6, 9, 12, 21, 45, or 69 h in water, and the metribuzin metabolism was studied in the cotyledons. The synergist did not interfere with herbicide uptake but did strongly inhibit metribuzin metabolism. The pathway of metribuzin metabolism in ivyleaf morningglory is discussed as well as the way it is affected by the synergist MZH 2091.
