Factors affecting toxicity, absorption, and translocation of glyphosate inredvine (Brunnichia ovata)

Greenhouse and growth chamber experiments were conducted to study glyphosat e efficacy, rainfastness, absorption, and translocation in redvine. Glyphos ate at 0, 0.56, 1.12, 2.24, and 4.48 kg ai/ha was applied to redvine plants raised from rootstocks at the five- to seven-leaf stage (about 25 cm tall) . Redvine control ranged from 55% at 0.56 kg/ha glyphosate to 98% at 4.48 k g/ha. Glyphosate at rates above 1.12 kg/ha, greatly reduced regrowth from r ootstocks of treated plants. A simulated rainfall of 2.5 cm (7.5 cm/h inten sity) within 24 h of glyphosate application reduced efficacy by 23% compare d with no simulated rainfall. Absorption of C-14-glyphosate in redvine incr eased from 1.8 to 21.9%, and translocation increased from 0.1 to 8.1% from 6 to 192 h after application, respectively. Translocation was both acropeta l and basipetal, and by 96 h of exposure, the C-14 radioactivity was widely distributed throughout the plant. Absorption and translocation was greatly affected by posttreatment temperature. Absorption and translocation were h ighest (34.9 and 10.6%, respectively) in plants maintained at 35/30 C (14/1 0 h, day/night), followed by 15/10 C (21.2 and 4.9%, respectively), and was lowest (7.8 and 1.6%, respectively) in plants maintained at 25/20 C. Resul ts suggest that longer periods of leaf exposure to the herbicide and high t emperatures could increase glyphosate absorption, translocation to redvine rootstocks, and subsequent control. These data also suggest that effective control of redvine in the held will require glyphosate rates higher than th ose recommended for use in glyphosate-resistant crops.