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1 October 2002 Evaluation of Reduced Rates of Glyphosate and Chlorimuron in Glyphosate-Resistant Soybean (Glycine max)
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Abstract: Field studies were conducted over 2 yr in Louisiana to evaluate entireleaf morningglory and hemp sesbania control by glyphosate isopropylamine salt applied alone at 420, 560, and 700 g ae/ha and in combination with chlorimuron at 4, 6, 9, and 11 g ai/ha. Comparison treatments included glyphosate alone at 840 g/ha, glyphosate at 1,400 g/ha plus chlorimuron at 13 g/ha, and sethoxydim at 210 g ai/ha plus chlorimuron at 11 g/ha. Entireleaf morningglory and hemp sesbania were controlled no more than 77% with glyphosate rates as high as 840 g/ha. Chlorimuron added to glyphosate increased entireleaf morningglory control in two of the three experiments to 83 to 88% and hemp sesbania control to 86 to 98%. Response to chlorimuron was not rate dependent. In most cases, glyphosate–chlorimuron mixtures did not antagonize barnyardgrass control, and increasing rate of glyphosate did not always increase control. Soybean was injured no more than 6% by chlorimuron at one location, but injury was as great as 30% at another location, which was possibly due to smaller soybean size. Differences in weed control and soybean injury among the glyphosate and glyphosate–chlorimuron combinations were not reflected in soybean yields. Because injury occurred early season, sufficient time remained for soybean to recover and produce acceptable yields. Weed control by sethoxydim plus chlorimuron was less consistent than that by glyphosate plus chlorimuron, and soybean yield in most cases was inferior to the glyphosate treatments.

Nomenclature: Chlorimuron; glyphosate; sethoxydim; barnyardgrass, Echinochloa crus-galli (L.) Beauv. #3 ECHCG; entireleaf morningglory, Ipomoea hederacea var. integriuscula Gray # IPOHG; hemp sesbania, Sesbania exaltata (Raf.) Rydb. ex. A. W. Hill # SEBEX; soybean, Glycine max (L.) Merr.

Additional index words: Herbicide mixtures, transgenic soybean.

Abbreviation: WAT, week after treatment.

P. ROY VIDRINE, JAMES L. GRIFFIN, and DAVID C. BLOUIN "Evaluation of Reduced Rates of Glyphosate and Chlorimuron in Glyphosate-Resistant Soybean (Glycine max)," Weed Technology 16(4), 731-736, (1 October 2002).[0731:EORROG]2.0.CO;2
Published: 1 October 2002
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