Objectives & Significant Accomplishments

1. Compare Roundup Ready weed control systems to conventional systems.
2. Determine the performance of these two systems in three Roundup Ready varieties and three of the top-yielding conventional varieties.
3. Compare the economics of these systems.

Studies were conducted to compare Roundup Ready to conventional soybean systems for efficacy and economics. The three highest yielding Roundup Ready and conventional cultivars were chosen for three Mississippi locations: Shelby (irrigated, Sharkey clay soil), Stoneville (non-irrigated, Sharkey clay soil), and Brooksville (non-irrigated, Black Belt clay soil). Cultivars were selected based on the 1996 Mississippi Soybean Variety Trials for these locations and soil types. Treatments within each cultivar- herbicide system included untreated, reduced, labeled, and chemical weed-free levels of input.

Pitted morningglory (Ipomoea lacunosa L.) and hemp sesbania [Sesbania exaltata (Raf.) Rydb.] were the predominant species at all locations. The reduced or labeled rates of the conventional system controlled pitted morningglory more than the comparable glyphosate treatments at Shelby and Brooksville 9 weeks after planting (WAP). At Stoneville, the Roundup Ready system controlled pitted momingglory better than the conventional system at labeled or chemical weed-free input levels. Control of pitted morningglory increased at the labeled rate of glyphosate when compared to the reduced rate at Shelby and Stoneville. Within the conventional system, control was not increased by the labeled rate compared to the reduced rate. At the reduced rates, hemp sesbania was controlled better with the conventional systems than glyphosate at all locations. However, at Stoneville the labeled rate of glyphosate controlled hemp sesbania better compared to the conventional system. Control of hemp sesbania was increased by the labeled rate of glyphosate in comparison of the reduced rate at all locations. There were no differences in the conventional system for hemp sesbania control between the labeled and reduced rate input levels.

Yield in the glyphosate reduced rate system was more than the similar conventional system at Stoneville. Yields from the glyphosate labeled rate system were higher than the comparable conventional system at Shelby and Stoneville. There were no differences in yields among the reduced and labeled rate input levels at Brooksville for either system. Within the Roundup Ready system, there were no yield differences between the reduced and labeled rate input levels. Yields of the conventional reduced rate input level were greater than the conventional labeled rate input level at Shelby.

Within the Roundup Ready system, net returns were not different between the reduced and labeled rate input levels at any location. Within the conventional system, the reduced rate input level net returns were more than the labeled rate systems at Shelby and Stoneville. Net returns of the glyphosate reduced rate system level were more than $40.00/A higher than the comparable conventional system at Stoneville. Net returns were more than $60.00/A higher with the labeled rate glyphosate system at both Shelby and Stoneville compared to the labeled rate conventional system.

Soybeans in Mississippi Mississippi Agricultural and Forestry Experiment Station  Mississippi State University Extension Service Division of Agriculture, Forestry and Veterinary Medicine

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