Imazethapyr-based weed control treatments were evaluated in water-seeded imidazolinone-resistant (IR) rice in Louisiana in 2000 and 2001. Treatments included imazethapyr applied to soil before seedling flood (surface [SURF] applied) or no soil application (no SURF), followed by imazethapyr applied postemergence (POST). Averaged over SURF application treatments (SURF, no SURF), all imazethapyr mixtures increased control of barnyardgrass at 14 and 42 d after POST treatment (DAT) compared with imazethapyr alone. Treatments containing imazethapyr-applied SURF followed by POST treatments controlled red rice 90 to 96% at 21 DAT. Alligatorweed and hemp sesbania control increased with POST mixtures compared with imazethapyr-only treatments at 35 DAT. Rice yield increased with imazethapyr applied SURF compared with no SURF application, averaged over POST applications. Other herbicides will be required to control troublesome weeds such as hemp sesbania and alligatorweed in an IR rice production system.
Nomenclature: Imazethapyr; alligatorweed, Alternanthera philoxeroides (Mart.) Griseb. #3 ALRPH; barnyardgrass, Echinochloa crus-galli (L.) Beauv. # ECHCG; hemp sesbania, Sesbania exaltata (Raf.) Rydb. ex A.W.Hill # SEBEX; red rice, Oryza sativa L. # ORYSA; rice, Oryza sativa L. ‘93 AS-3510’, ‘CL 121’.
Additional index words: Acetolactate synthase, Clearfield rice, herbicide mixtures.
Abbreviations: ALS, acetolactate synthase (EC 188.8.131.52); DAT, days after postemergence treatment; IR, imidazolinone-resistant; POST, postemergence; PPI, preplant incorporated; PRE, preemergence; SURF, surface.