Field research was conducted for 3 yr to evaluate crop response and weed control under conventional and reduced tillage in drill- and water-seeded imidazolinone-tolerant (IT) rice culture. Imazethapyr was applied at 70 g ai/ha PRE followed by (fb) imazethapyr at 70 g/ha applied POST to three- to four-leaf rice or at 105 g/ha PRE fb 70 g/ha POST. In both conventional and reduced tillage systems, imazethapyr applied PRE fb POST at 70 g ai/ha controlled red rice, barnyardgrass, Amazon sprangletop, and rice flatsedge 87 to 99% 35 d after POST treatment (DAT). At 35 DAT, Indian jointvetch control with sequential applications of imazethapyr was as high as 70% in water-seeded rice but no more than 54% in drill-seeded rice. Tillage, seeding method, and imazethapyr rate had no effect on days to 50% heading, seeds per panicle, seed weight per panicle, or percentage of seed harvest. However, a reduction of 27% in days to 50% heading, 80% in seeds per panicle, 84% in seed weight per panicle, and 100% in percentage seed harvest index occurred when imazethapyr was not applied because of weed interference. Culm number was reduced 28%, and culm weight 32% under reduced tillage compared with conventional tillage. With sequential applications of imazethapyr at 70 g/ha, rice yield was 63% greater when rice was water-seeded compared with drill-seeded. No differences in tillage systems for weed control, days to 50% heading, seed number, seed weight per panicle, percent seed, panicle height, lodging, or yield were observed. Results of these experiments demonstrate imazethapyr will effectively control weeds in both water- and drill-seeded rice and that reduced tillage can be used without negatively affecting rice production.
Nomenclature: Imazethapyr; Amazon sprangletop, Leptochloa panicoides (Presl) Hitchc. #3 LEFPA; barnyardgrass, Echinochloa crus-galli (L.) Beauv. # ECHCG; Indian jointvetch, Aeschynomene indica L. # AESIN; red rice, Oryza sativa L. # ORYSA; rice flatsedge, Cyperus iria L. # CYPIR; rice, Oryza sativa L. ‘93-AS-3510’, ‘CL121’.
Additional index words: Conventional tillage, crop injury, drill-seeded rice, reduced tillage, water-seeded rice.
Abbreviations: ALS, acetolactate synthase (E.C.4.1.3.18).
