The potassium salt of 4-amino-3,5,6-trichloropicolinic acid (picloram) was applied as soil, foliar, and soil plus foliar treatments to defoliated and non-defoliated huisache (Acacia farnesiana (L.) Willd) grown in the greenhouse. Soil applications of ⅛ lb/A were more effective than foliar treatments. However, soil or foliar applications at ½ lb/A were lethal on non-defoliated plants. Defoliated plants treated with ½ lb/A showed considerable regrowth, indicating that leaves were important for absorption and movement of the herbicide into stem and root tissues. Plants treated with ¼ lb/A of picloram and defoliated after 0, 4, 10, and 24 hr indicated that 24 hr were necessary to obtain maximum herbicidal effectiveness.

Picloram content was determined in the leaves, upper stem, lower stem, and roots by gas chromatographic analysis, 3, 10, and 30 days after treatment. Most of the picloram applied to foliage was found in and on the leaves 30 days after treatment. The upper stem contained several times more picloram than the lower stem. No detectable amounts of picloram were found in the leaves and upper stem 3 and 30 days after soil treatment. The concentration of picloram in roots from soil applications was similar to foliar treatments. Absorption and movement studies showed that a period of 24 hr was required to move lethal amounts of picloram into stem and root tissues of huisache after foliar treatments.