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 fores t managers. Many factors influence the efficacy of herbicides, includi ng the physiological status of the plant and its effect on the translo cation of herbicides. This study investigated how plant moisture statu s affected herbicide absorption and translocation. The ester formulati on of [C-14]triclopyr was applied to the foliage of 8-month-old, conta iner-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. Correspon ding seedling xylem water potentials averaged -1.8 and -0.3 MPa, respe ctively. Triclopyr absorption was not significantly affected by the so il moisture treatment. However, translocation to stems and roots was 6 2 and 48% lower, respectively, in water-stressed seedlings. Water oak absorbed 23% less than southern red oak when averaged over the soil mo isture treatments. Scheduling herbicide applications when moisture is plentiful could improve triclopyr efficacy.