Effect of Flood Timing on Red Rice (Oryza spp.) Control with Imazethapyr Applied at Different Dry-Seeded Rice Growth Stages1

Field experiments were conducted in 2002 and 2003 in Beaumont, TX, to evaluate the effect of flood timing on red rice control with imazethapyr applied at different cultivated rice growth stages. Treatments included flood establishment at 1, 7, 14, and 21 d after postemergence (POST) herbicide treatment (DAT). Imazethapyr was applied preemergence at 70 g ai/ha followed by 70 g/ ha POST when imidazolinone-tolerant rice cultivar ‘CL-161’ had three- to four-leaf stage (EPOST) or five-leaf stage (LPOST). Flood needed to be established within 14 DAT to achieve at least 95% red rice control when imazethapyr was applied EPOST. However, flood needed to be established within 7 DAT to provide at least 95% red rice control when imazethapyr was applied LPOST. Delaying the flood up to 21 DAT reduced rice grain yield for both application timings. Nomenclature: Imazethapyr; red rice, Oryza sativa L., #ORYSA3; rice, Oryza sativa L., cultivar ‘CL-161.’ Additional index words: Acetolactate synthase (EC 4.1.3.18), ALS inhibitor, Clearfield rice, imidazolinone, water management. Abbreviations: ANOVA, analysis of variance; DAPOST, days after postemergence treatments; DAT, days after treatment; EMS, ethyl methanesulfonate; EPOST, early postemergence; LPOST, late postemergence; POST, postemergence; PRE, preemergence.