Field experiments were conducted near Beaumont, TX, to evaluate red rice control in imidazolinone-tolerant rice. Imazethapyr was applied preplant incorporated (PPI) and preemergence (PRE) at 70 and 105 g ai/ha and postemergence (POST) at 36, 52, and 70 g/ha. Single imazethapyr applications were made at each rate and timing and in sequential PPI or PRE followed by POST treatments. Red rice control ranged from 92 to 98% with sequential imazethapyr applications. Red rice control was higher when imazethapyr was applied PPI alone than PRE alone. But when these treatments were followed by a POST application of imazethapyr, there were no differences in red rice control between PPI and PRE application. Red rice control with sequential treatments was not improved with increased rates of imazethapyr POST. Visual injury to the 93AS3510 imidazolinone-tolerant variety was 5% or less 20 d after treatment (DAT), and there was no injury by 45 DAT. But POST applications of 70 g/ha imazethapyr may produce minor yield reductions to this experimental variety without improving red rice control. Results indicate that an imidazolinone-tolerant rice production system can be effective for controlling red rice and that PRE applications must be followed by a POST application to achieve maximum red rice control. PPI applications of imazethapyr at 70 g/ha should also be followed by a POST application to maximize red rice control.
Nomenclature: Imazethapyr; red rice, Oryza sativa L. # ORYSA ‘93AS3510’; rice, Oryza sativa L. #3 ORYSA.
Additional index words: Clearfield rice, imidazolinone-tolerant rice, Newpath, red rice control.
Abbreviations: DAT, days after treatment; POST, postemergence; PPI, preplant incorporated; PRE, preemergence.
