Comparison of Weed Management Systems in Narrow-Row, Glyphosate- and Glufosinate-Resistant Soybean (Glycine max)1

Abstract

Field experiments were conducted near DeKalb and Urbana, IL, and Columbia, MO, in 1997 and 1998 to evaluate weed management systems in glyphosate- and glufosinate-resistant soybean planted in 18-cm rows. Overall weed control was improved to a greater extent when the rate of glufosinate was increased from 300 to 400 g ai/ha than when the rate of glyphosate increased from 630 to 840 g ae/ha. Sequential applications of glufosinate improved control over single applications, whereas sequential treatments of glyphosate generally provided no advantages over single applications. When averaged across all weed species in these trials, the systems that provided 95% or higher average control were sequential applications of glufosinate, sequential applications of glyphosate, and clomazone followed by (fb) glyphosate. Single applications of glufosinate provided somewhat variable control of giant foxtail, common lambsquarters, ragweed, and common cocklebur similar to that observed with pendimethalin fb imazethapyr. The addition of fomesafen to glufosinate did not improve control of any of the weeds in this study with the exception of velvetleaf at DeKalb. The addition of clomazone to glufosinate treatments resulted in slightly better giant foxtail and velvetleaf control. Single applications of glyphosate provided somewhat variable control of giant ragweed at DeKalb in 1997 and ivyleaf morningglory and common cocklebur control at Columbia. The addition of fomesafen to glyphosate provided an increase in ivyleaf morningglory and common cocklebur control at Columbia but did not improve control of any other species. The addition of clomazone to glyphosate-based programs resulted in slightly higher velvetleaf, common cocklebur, and ivyleaf morningglory control. In the glyphosate-based herbicide programs there were no substantial differences in relative yield, with all programs protecting over 95% of soybean yield. Glufosinate-based programs were effective in protecting 85 to 92% of soybean yield.Nomenclature: Clomazone; fomesafen; glyphosate; glufosinate; imazethapyr; pendimethalin; common cocklebur, Xanthium strumarium L. #3 XANST; common lambsquarters, Chenopodium album L. # CHEAL; giant foxtail; Setaria faberi Herrm. # SETFA; giant ragweed, Ambrosia trifida L. # AMBTR; ivyleaf morningglory, Ipomoea hederacea L. Jacq. # IPOHE; velvetleaf, Abutilon theophrasti Medic. # ABUTH; soybean, Glycine max (L.) Merr.Abbreviations: EPOST, early postemergence; fb, followed by; LPOST, late postemergence, POST, postemergence; PRE, preemergence; UAN, 28% urea ammonium nitrate.