Carrier Volume Affects Wheat Response to Simulated Glyphosate Drift

The influence of carrier volume was evaluated in field experiments for glyphosate applied to wheat at rates representing 12.5 and 6.3% of the usage rate of 1,120 g ai/ha (140 and 70 g/ha, respectively). Wheat at first node and at heading was exposed to glyphosate applied in a constant carrier volume of 234 L/ha, where herbicide concentration declined with reduction in dosage, and in proportional carrier volumes of 30 L/ha for the 12.5% rate and 15 L/ha for the 6.3% rate, where herbicide concentration remained constant. At 28 d after treatment, glyphosate applied at first node in proportional carrier volume (an average for 30 and 15 L/ha adjusted proportionally to glyphosate rate) reduced wheat height 42% compared with 15% when glyphosate was applied in 234 L/ha. Height reduction was no more than 15% when glyphosate was applied at heading in 234 L/ha or in the proportional carrier volumes and at first node in 234 L/ha. Wheat yield was reduced 42% when glyphosate at 140 g/ha was applied in 234 L/ha but was ...