Response of nonglyphosate-resistant cotton to reduced rates of glyphosate

Document Type

Article

Publication Date

12-1-2004

Abstract

Field research was conducted in 1999 and 2000 to determine the effect of reduced glyphosate rates on growth and yield of nonglyphosate-resistant cotton. Rates of 9, 18, 35, 70, 140, and 280 g ha-1, representing 0.008, 0.016, 0.031 0.063, 0.125, and 0.25, respectively, of the maximum use rate per application (1,120 g ha-1), were applied to cotton at the two-, five-, or nine-node growth stage. On the basis of visual injury estimates, cotton was more tolerant to glyphosate at the nine-node than at earlier growth stages. Plant dry weight was reduced with 70 g ha-1 of glyphosate or higher, when applied at the two- and five-node growth stages in two of three experiments. Dry weight was not affected by glyphosate at the nine-node stage. Plant height also was unaffected by glyphosate rates below 70 g ha-1, but height reduction was noted for all growth stages by experiment combinations, with the exception of the nine-node application for both experiments in 2000, with herbicide rates of 70 g ha-1 or higher. Cotton maturity delay, as noted by an increase in node above white flower number, was observed only at the highest glyphosate rate applied to two- and five-node cotton in one of three experiments. Percent open boll data analysis indicated a decreased opportunity of observing an open boll with increasing glyphosate rate, and this effect was greater at the five-node compared with the two-and nine-node stages in two of three experiments. Seedcotton yield after all glyphosate applications was equivalent to that for the nontreated control.

Publication Source (Journal or Book title)

Weed Science

First Page

178

Last Page

182

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