Two studies were designed to test three herbicides and factors which influence their efficacy. In the first study four chemical combinations used for site preparation in southern pine, including triclopyr (3,5,6-trichloro-2-pyridinyloxyacetic acid), trichloropicolinic acid), dichlorophenoxy)acetic acid] picloram (4-amino-3,5,6- and 2,4-D [(2,4- were screened for the most effective control of selected hardwoods. The chemical combinations were tested on Piedmont and Coastal Plain physiographic sites and were examined for the optimum amount of time for chemical activity between application and slash disposal (site disturbance). Efforts were also made to use target-plant and environmental data to predict chemical efficacy. A combination of triclopyr and picloram at 2 and 1 lb ai/ac, respectively, each gave the best overall control of hardwood brush. The amount of time required to obtain the optimum chemical control, presumably related to translocation, was found to be six to eight weeks after application to the foliage. Chestnut oak (Quercus prinus L.) control was successfully predicted on the bases of plant tissue and environmental data. In a second study the effect of temperature and time on the distribution of foliar-applied triclopyr, picloram, and 2,4-D were observed in red maple (Acer rubrum L.). Detection of the herbicides in the stems and roots using gas chromatography revealed that triclopyr was less affected by temperature differences; however, overall more herbicide reached the roots of red maple growing in a 21° C than those growing in a 29° C temperature. Triclopyr concentrations in the roots reached a peak much earlier than picloram or 2,4-D which did not peak until 42 days after application. / M.S.