Effects of Frost and Maturity on Glyphosate Phytotoxicity, Uptake, and Translocation

The effect of temperatures below 0 C and plant maturity on the phytotoxicity of glyphosate [N-(phosphonomethyl)glycine] on rapidly growing alfalfa (Medicago sativa L. ‘Vernal’) and quackgrass [Agropyron repens (L.) Beauv.] plants was studied in a controlled environment. Pretreatment at −4 C partially protected alfalfa from injury by 0.8 kg/ha of glyphosate at six alfalfa maturities. This same treatment had no significant effect on glyphosate phytotoxicity to quackgrass. Pretreatment at −4 C increased translocation of glyphosate in quackgrass but reduced its translocation in alfalfa. A greater reduction in translocation occurred in the smaller alfalfa plants.