Correlation of environment and root carbohydrate content to picloram translocation in leafy spurge

Abstract

14C-picloram (4-amino-3,5,6-trichloro-2-pyridinecarboxylic acid) absorption and translocation in leafy spurge (Euphorbia esula L.) was evaluated over 2 growing seasons and was compared to selected environmental parameters and root carbohydrate content. 14C-picloram absorption was greatest during the vegetative growth stage (52%) and increased directly with relative humidity but was not affected by the temperature at treatment. 14C-picloram translocation to leafy spurge roots generally was influenced more by the plant growth stage than the environment. The greatest translocation to roots occurred during the true-flower and seed-set growth stages. The water-soluble (monosaccharide and disaccharide) and water insoluble carbohydrate content in leafy spurge roots average across the growing season varied by depth with the lowest amount in the 0- to 8-cm depth, 35 and 53 mg/g, and the most in the 16- to 24-cm depth 84 and 221 mg/g, respectively. 14C-picloram translocation to leafy spurge roots was independent of either carbohydrate fraction when evaluated over the entire growing season. However, 14C-picloram content increased when the water-soluble fraction increased during the true-flower growth stage. 14C-picloram translocation to the roots did not increase in the fall, in contrast to the general hypothesis that herbicides move with photosynthates to the roots.