Use of Imazethapyr in Water-Seeded Imidazolinone-Tolerant Rice (Oryza sativa)1

A study was established to evaluate weed control and crop response of imidazolinone-tolerant (IMI-tolerant) rice in water-seeded culture with imazethapyr at 70, 105, and 140 g ai/ha at four different soil application timings with or without 70 g/ha imazethapyr postemergence (POST). Application timings included preplant incorporated (PPI), surface application prior to seeding (SURFACE), following seeding (SEED), and at pegging (PEG). The PEG treatments were applied when green leaf tissue had emerged from the seed and the root had begun to extend downward into the soil. Response of barnyardgrass, red rice, and rice injury was not affected by the addition of an imazethapyr POST application. Barnyardgrass control was above 90% at 28 d after treatment (DAT) for both years. At 42 DAT, barnyardgrass control decreased to 88% in 1998, compared with 94% control in 1999. Averaged over years, Indian jointvetch control ranged from 44 to 74% at 28 DAT and 41 to 71% at 42 DAT. Indian jointvetch control was inconsistent and lacked uniformity over all factors. Rice injury increased as application timing was delayed from PPI to PEG in 1998 at both rating dates. In 1999, injury was not observed with imazethapyr at 28 DAT, and 1% injury was observed at 42 DAT with all imazethapyr application timings.Nomenclature: Imazethapyr; Barnyardgrass, Echinochloa crus-galli (L.) Beauv. #3 ECHCG; Indian jointvetch, Aeschynomene indica L. # AESIN; rice Oryza sativa L, ‘93 AS-3510’.Additional index words: ALS, acetolactate synthase, Clearfield rice, soil-applied herbicide.Abbreviations: ALS, acetolactate synthase (E.C. 4.1.3.18); DAT, d after POST treatment; IMI-tolerant, imidazolinone-tolerant; PEG, pegging; POST, postemergence; PPI, preplant incorporated; PRE, preemergence; SEED, following seeding; SURFACE, surface application prior to seeding.