Master of Science (MS)
Plant, Environmental Management and Soil Sciences
Field research evaluated response of ‘USG 3209’ wheat to glyphosate drift representing 12.5, 6.3, and 1.6% of the usage rate of 1,120 g ai/ha (140, 70, and 18 g/ha, respectively). Applications in 140 L/ha spray volume were made at first node in late February/late March, boot stage in late March/early April, and early flowering in early to mid-April. Bleaching of leaf foliage was observed for all glyphosate rates regardless of application timing. Height 28 days after treatment (DAT) was reduced 47% with glyphosate applied at 140 g/ha at first node and around 26% for 70 g/ha applied at first node or 140 g/ha applied at boot stage. Yield was reduced 72% when glyphosate was applied at 140 g/ha at first node, 45% when applied at boot stage, and 54% when applied at flowering. For 70 g/ha wheat yield was reduced 25 to 30% for the three application timings, but yield was not reduced for 18 g/ha. In another study, response of six wheat varieties to glyphosate was the same as that observed for USG 3209. The influence of carrier volume was evaluated where glyphosate at drift rates representing 12.5 and 6.3% of 1,120 g/ha was applied to USG 3209 wheat at first node in late February/late March and at heading in early to mid April. Glyphosate was applied in constant carrier volume of 234 L/ha where herbicide concentration declined with reduction in dosage and in carrier volumes adjusted proportionally to glyphosate rate to include 30 L/ha for 12.5% rate and 15 L/ha for 6.3% rate. Glyphosate applied at first node in proportional carrier volume reduced height 42% 28 DAT, 2.8 times the reduction for glyphosate applied in 234 L/ha. Height reduction was no more than 15% when glyphosate was applied at heading regardless of carrier volume. Yield was reduced 42% when glyphosate at 140 g/ha was applied in 234 L/ha, but was reduced 54% when applied in proportional carrier volume. For 70 g/ha glyphosate applied in 234 L/ha yield was reduced 11%, but yield reduction was almost 4 times greater when applied in proportional carrier volume.
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Roider, Christopher Andrew, "Wheat (Triticum aestivum) response to simulated drift of glyphosate" (2006). LSU Master's Theses. 737.
James L. Griffin