Concentration of 2,4,5-T, Triclopyr, Picloram, and Clopyralid in Honey Mesquite (Prosopis glandulosa) Stems

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Abstract
Triclopyr {[(3,5,6-trichloro-2-pyridinyl)oxy] acetic acid}, 2,4,5-T [(2,4,5-trichlorophenoxy)acetic acid], picloram (4-amino-3,5,6-trichloro-2-pyridinecarboxylic acid), and clopyralid (3,6-dichloro-2-pyridinecarboxylic acid) were applied to honey mesquite (Prosopis glandulosa Torr. # PRCJG) on seven different dates about every 3 weeks from May to September in 1980 and 1981. Concentrations of 2,4,5-T or triclopyr in stem tissue were usually less than 2 μg/g fresh weight regardless of date of application. Concentrations of picloram and clopyralid were as high as 11 and 22 μg/g fresh weight, respectively, in upper stem phloem at some dates of application. Higher concentrations of all herbicides were detected in upper stem phloem than in the upper stem xylem or basal stem phloem or xylem. More herbicide tended to be detected in stems when herbicides were applied early (May and June) than late (August and September) in the season. Concentrations of triclopyr and picloram recovered from honey mesquite stems were about 25% greater at 3 than at 30 days after treatment, whereas concentrations of 2,4,5-T and clopyralid were about 50% greater at 3 than at 30 days after application.