EFFECT OF BUD VS ROSETTE GROWTH STAGE ON TRANSLOCATION OF C-14 GLYPHOSATE IN CANADA THISTLE (CIRSIUM-ARVENSE)

The effect of photoperiod and growth stage on translocation of C-14-gl yphosate was compared in Canada thistle plants at the bud and rosette stage of growth. Canada thistle plants grown under controlled environm ent conditions with a 10 h photoperiod remained as low growing rosette s and developed a mature root system. When the photoperiod for half of these plants was increased to 16 h, stem elongation occurred and flow ering was initiated. Growth stage at the time of application affected the distribution of C-14-glyphosate within the elongated shoot and bet ween the shoot and root. The shoot tissue of the bud stage plants cont ained 25.9% of the C-14-glyphosate recovered, while the rosette plants contained only 3.6%; a seven-fold difference. C-14-glyphosate was app lied to leaves 19 and 20, which corresponded to the mid-point of the e longated stem of the bud-stage plants. In the bud-stage plants, C-14-g lyphosate moved preferentially into the apical portion of the stem, wi th three to four times as much in the apical portion of the elongated stem as in the basal portion. In the roots, the effect of growth stage on distribution of C-14-glyphosate was reversed, application at the r osette stage resulted in a four-fold increase in the amount of C-14-gl yphosate in the root. When applied in the rosette stage, 19.1% of the C-14- glyphosate detected was in the root compared to only 4.9% when a pplied at the bud stage. Although the root of the rosette plants was l arger than in bud-stage plants, the concentration of C-14-glyphosate i n the root tissue of the rosette plants was three times greater. Photo period indirectly affected the distribution of C-14-glyphosate in Cana da thistle by its effect on growth.