Submitted to: Weed Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/3/1999
Publication Date: N/A
Interpretive Summary: With the introduction of glyphosate-resistant (Roundup Ready) and sulfonylurea-tolerant soybeans, producers are wondering whether these weed control systems are efficient and profitable. Information from side-by-side comparisons of various soybean systems is lacking. A two-year field study was conducted by the Southern Weed Science Research Unit, Stoneville, MS to compare weed control efficiency and economics of glyphosate-resistant, sulfonylurea-tolerant, and conventional soybean weed control systems. Herbicide treatments within each soybean system provided satisfactory control of most common annual weeds, including certain difficult weeds such as yellow nutsedge, pitted morningglory, hemp sesbania, prickly sida and hyssop spurge compared to untreated plots. Control of prickly sida and hyssop spurge was somewhat variable in sulfonylurea-tolerant soybeans. If weed control was satisfactory and herbicide costs were comparable, soybean yield level was the determining factor in net profitability regardless of soybean system. Variety selection is a critical management factor, and high yield potential continues to be the best criterion for selecting a variety. The next most critical decision is to select a herbicide program that is compatible, effective, and economical.
Technical Abstract: A two-year field study was conducted in 1997 and 1998 at the Southern Weed Science Research Unit Farm, Stoneville, Mississippi on a Dundee silty clay loam to compare weed control efficiency and economics of glyphosate-resistant, sulfonylurea-tolerant, and conventional soybean weed control systems. Herbicide treatments provided > 90% control of browntop millet, yellow nutsedge, pitted morningglory, and hemp sesbania compared to untreated plots regardless of soybean systems in both years. Prickly sida control among three soybean systems with various herbicides was > 98% in both years except for 65% control in sulfonylurea-tolerant soybean system with chlorimuron (POST1 + POST2) in 1997. Control of hyssop spurge with herbicides ranged from 93 to 100% in glyphosate resistant soybean system and from 88 to 100% in conventional soybean system in both years. However, in sulfonylurea-tolerant soybean system, control of hyssop spurge was variable. In 1997, sulfentrazone (PRE) + chlorimuron (PRE) plus chlorimuron (POST1) controled 100% hyssop spurge compared to 63 to 86% control with other herbicides. In 1998, sicklepod control was > 91% regardless of soybean systems except in conventional soybean with dimethenamid + imazaquin PRE followed by acifluorfen + bentazon POST. Soybean yield in glyphosate-resistant soybean system with glyphosate applied POST1 + POST2 was 2876 and 3161 kg/ha with a net return of 464 and 350 $/ha, respectively in 1997 and 1998. In sulfonylurea-tolerant soybean system, chlorimuron applied POST1 + POST2 yielded 2391 and 2605 , kg/ha resulting a net return of 298 and 245 $/ha, respectively in 1997 and 1998.