Glyphosate Injury, Rainfastness, Absorption, and Translocation in Purple Nutsedge (Cyperus rotundus)

Greenhouse and laboratory experiments were conducted to study activity, rainfastness, absorption, and translocation of glyphosate with and without a nonionic organosilicone surfactant in purple nutsedge. Purple nutsedge responded differently to glyphosate depending on growth stage. Glyphosate at 2.24 kg ai/ha in 17-d-old and at 4.48 kg/ha in 10-wk-old plants controlled purple nutsedge at least 96%. Regrowth of plants and tuber resprouting were greatly reduced in these treatments. Organosilicone surfactant did not increase efficacy of glyphosate. A simulated rainfall of 2.5 cm (7.5 cm/h intensity) at 1 and 24 h after glyphosate application reduced efficacy by one-half and one-third, respectively, compared with no simulated rainfall. A rain-free period of 72 h prevented loss of glyphosate activity. Absorption of 14 C-glyphosate increased from 2.8% at 1 h after application to 21.4% at 168 h after application and translocation increased from 0.43% at 1 h after application to 5.18% at 168 h after application. Organosilicone surfactant did not affect absorption and translocation of glyphosate in purple nutsedge.