Mode of Clopyralid Uptake by Honey Mesquite (Prosopis glandulosa)

Leaves absorbed high amounts of clopyralid (3,6-dichloro-2-pyridinecarboxylic acid) as foliar sprays on honey mesquite (Prosopis glandulosaTorr. # PRCJG) as indicated by concentrations of 10 μg/g fresh wt or more in basal stem phloem by 4 days after treatment. Small quantities of clopyralid (< 1 μg/g) were detected in basal stem phloem after spray applications of clopyralid to defoliated plants or roots treated by soil application. When applied to foliated plants, the 0.56 kg/ha of clopyralid killed 60% or more plants, but none were killed when clopyralid sprays were applied to defoliated plants or when 2.2 kg/ha of clopyralid was applied to the soil. Water, diesel oil plus water, or water plus surfactant were equally effective as clopyralid carriers as foliar sprays.