Graminicide Application Timing Influences Red Rice (<i>Oryza sativa</i>) Control and Seedhead Reduction in Soybean (<i>Glycine max</i>)¹

Abstract

Several graminicides were evaluated at various application timings for control and seedhead suppression of red rice (Oryza sativa) in soybean (Glycine max). One application of clethodim, fluazifop-P, quizalofop-P, or sethoxydim at any timing did not control red rice more than 86% 2 wk after treatment. Emergence of red rice seedlings subsequent to applications reduced control later in the season. At a naturally infested location, seedhead reduction was greatest, regardless of graminicide, when application was delayed until the four-leaf stage. At a second location, seedhead reductions were highest following graminicide applications at the two-leaf stage of growth. No single graminicide application completely eliminated red rice seedhead production. Soybean yields were reduced when graminicide application was delayed until the boot stage at both locations, and following two-leaf stage applications at the naturally infested location.Nomenclature: Clethodim, (E,E)-(±)-2-[1-[[(3-chloro-2-propenyl)oxy]imino]propyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one; fluazifop-P, (R)-2-[4-[[5-(trifluoromethyl)-2-pyridinyl]oxy]phenoxy]propanoic acid; quizalofop-P, (R)-2-[4-[(6-chloro-2-quinoxalinyl)oxy]phenoxy]propanoic acid; sethoxydim, 2-[1-(ethoxyimino)butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one; red rice, Oryza sativa L. #3 ORYSA; soybean, Glycine max (L.) Merr. ‘Hartz 4464’ and ‘Terra-Vig 5452’.Additional index words: Clethodim, fluazifop-P, quizalofop-P, sethoxydim, ORYSA.Abbreviations: POST, postemergence; PPI, preplant incorporated; PRE, preemergence; WAT, weeks after treatment.