Carrier Volume Affects Wheat Response to Simulated Glyphosate Drift

Abstract

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 reduced 54% for the same rate applied in proportional carrier volume. For 70 g/ha glyphosate, wheat yield was reduced 11% when applied in 234 L/ha, but was reduced 42% when the same rate was applied in proportional carrier volume. Wheat yield reduction was equivalent when glyphosate was applied in 234 L/ha at first node and at heading (29 and 24%, respectively), but yield reductions of 60% for first node application and 36% for heading application were observed when glyphosate was applied in a proportional carrier volume. When averaged across carrier volumes and glyphosate rates, the greater yield loss from application at first node was attributed to decreased number of spikelets per spike and seed weight per spike.

Effect of Carrier Volume on Grain Sorghum Response to Simulated Drift of Nicosulfuron

“…In 2010, grain sorghum yield was reduced 73% when applied in the constant carrier volume of 224 L ha À1 compared to a yield reduction of 55% when applied in the proportional carrier volume averaged across 56, 28, and 14 L ha À1 . These data are in contrast to those previously reported for 2,4-D on cotton (Gossypium hirsutum L.) and for glyphosate on sweet corn (Zea mays L.) (Banks and Schroeder 2002) and for glyphosate on corn (Ellis et al 2002) and for glyphosate on wheat (Triticum aestivum L.) (Roider et al 2008). A possible explanation for this is the number of droplets deposited on the grain sorghum leaves.…”

“…These results showing greater yield reduction in 2012 are likely attributable to reduced rainfall during the growing season (Table 1), perhaps due to decreased herbicide metabolism as the plants adjusted to drier conditions. The increased yield reduction from the proportional carrier volumes agree with results reported for glyphosate (Banks and Schroeder 2002;Ellis et al 2002;Roider et al 2008) but disagrees with 2010 results. A possible explanation could be increased epicuticular wax loads on grain sorghum plants in 2012.…”

“…However, many grain sorghum production areas in Texas will likely experience conventional and herbicide-resistant grain sorghum varieties growing in close proximity. Previous research on simulated drift of herbicides has shown differences in injury and yield because of changes in carrier volumes (Ellis et al 2002;Roider et al 2008). Previous research has been conducted to evaluate simulated herbicide drift to grain sorghum from glufosinate, glyphosate, imazethapyr, and sethoxydim (Al-Khatib et al 2003).…”

2,4-D Past, Present, and Future: A Review

“…Herbicide effects from volatilization exposure would be more highly overestimated in these simulated drift experiments since spray exposure is chronic as opposed to an acute and transient vapor exposure (due to air mixing and lack of particle deposition). On the other hand, some herbicides can show an increased response when applied at lower spray volumes and therefore higher concentrations (Banks and Schroeder 2002;Roider et al 2008). However, these studies can be instructive for correlating visual symptoms with other plant parameters such as growth and grain yield.…”

Effects of spray drift of glyphosate on nontarget terrestrial plants—A critical review

“…It is likely that the practice of simulating spray drift by dilution rather than by using proportionally decreasing spray volumes has led to a significant underestimation of the negative effects of spray drift on plants in many cases, potentially by as much as a factor of 4, although this is difficult to ascertain. Roider et al found a wheat yield decrease of 11% when applying glyphosate at a rate of 70 g/ha and a spray volume of 234 L/ha but a decrease of 42% when glyphosate was applied in a proportional carrier volume of only 15 L/ha. Similarly, Ellis et al , using the same application rates and spray volumes, found a 4 times higher yield reduction of corn; and Banks and Schroeder obtained a >4 times lower no‐observed‐effect level value when using proportional carrier volumes compared with a constant one.…”