ABSORPTION AND TRANSLOCATION OF GLYPHOSATE IN ASPEN (POPULUS-TREMULOIDES MICHX) AS INFLUENCED BY DROPLET SIZE, DROPLET NUMBER, AND HERBICIDE CONCENTRATION

When herbicide concentration was constant, absorption of C-14-glyphosa te increased with increasing droplet size (326 to 977 mu m). Amount of C-14-glyphosate translocated away from the treated area, expressed as percent of absorbed, increased as droplet size decreased. Herbicide c oncentration of the droplet was more important than droplet number or droplet size in determining glyphosate absorption and translocation. A bsorption and translocation increased with increasing herbicide concen tration regardless of whether droplet size or number was altered in co njunction with herbicide concentration. This relationship explained wh y low spray volume (increased herbicide concentration) increased herbi cide efficacy. The concentration gradient between droplet and leaf, ra ther than droplet coverage, was the primary mechanism responsible for the observed effect. Large droplets caused localized tissue injury, wh ich may have caused decreased translocation.