UPTAKE AND TRANSLOCATION OF C-14 GLYPHOSATE IN ALTERNANTHERA-PHILOXEROIDES (MART) GRISEB (ALLIGATOR WEED) .1. RHIZOME CONCENTRATIONS REQUIRED FOR INHIBITION

Rhizome segments from Alternanthera philoxeroides were shaken in solutions of C-14-glyphosate for 24 h to establish a range of internal tissue concentrations. Rhizomes were killed at concentrations of 16 mug g-1 dry weight and above and survived at concentrations of 8 mug g-1 dry weight and below. Plants grown in the field for 10 weeks in declining photoperiod were used to investigate the uptake and translocation of C-14-glyphosate after application of a constant dosage in either 1.0- or 0.2-mul droplets corresponding to concentrations of 1.06 and 5.3 g l-1, of glyphosate acid, respectively. Use of smaller droplets of higher concentration increased absorption of C-14, but did not improve translocation. Uptake by treated leaves was 25 and 41% of the applied glyphosate for the large and small droplets respectively, but translocation to underground parts of the plant was about 7% of applied C-14-activity. Radiolabel accumulated in new rhizomes was equivalent to about 0.5 mug g-1 dry weight of glyphosate, at least 30 times below the concentration required for tissue death.