EFFECT OF PLANT MOISTURE STRESS ON ABSORPTION AND TRANSLOCATION OF TRICLOPYR IN OAK SEEDLINGS

Ways to maximize herbicide efficacy are of great concern to most forest managers. Many factors influence the efficacy of herbicides, including the physiological status of the plant and its effect on the translocation of herbicides. This study investigated how plant moisture status affected herbicide absorption and translocation. The ester formulation of [C-14]triclopyr was applied to the foliage of 8-month-old, container-grown water oak (Quercus nigra L.) and southern red oak (Quercus falcata Michx.) seedlings. At the time of treatment, seedlings were in soil with average moisture contents of 5 and 35% by weight. Corresponding seedling xylem water potentials averaged -1.8 and -0.3 MPa, respectively. Triclopyr absorption was not significantly affected by the soil moisture treatment. However, translocation to stems and roots was 62 and 48% lower, respectively, in water-stressed seedlings. Water oak absorbed 23% less than southern red oak when averaged over the soil moisture treatments. Scheduling herbicide applications when moisture is plentiful could improve triclopyr efficacy.