Abstract: A greenhouse study was conducted to evaluate the efficacy of imazethapyr at 35 and 53 g ai/ha applied preplant incorporated (PPI) or postemergence (POST) under various soil moisture regimes (13, 19, 25, and 50%) on barnyardgrass and red rice. Response of barnyardgrass and red rice to imazethapyr PPI was affected by soil moisture. With imazethapyr PPI, control of barnyardgrass was reduced at 50% soil moisture compared with other soil moisture regimes, and height of barnyardgrass increased as soil moisture increased from 19 to 50% 2 weeks after treatment (WAT). Barnyardgrass control declined and plant dry weight increased with the increase of soil moisture from 19 to 50% at 3 WAT. Imazethapyr PPI activity on red rice was reduced at 50% compared with other soil moisture regimes, as reflected by decreased control ratings as well as increased plant height and dry weight. Imazethapyr activity on barnyardgrass and red rice was increased at 50% soil moisture when applied POST compared with PPI. Imazethapyr POST activity on barnyardgrass and red rice was generally not affected by the soil moisture regimes or application rates. The results suggested that high soil moisture conditions reduced imazethapyr PPI efficacy on barnyardgrass and red rice. Imazethapyr POST activity seems unaffected by soil moisture conditions and thus may be used to control barnyardgrass and red rice if wet soil conditions are a concern.
Nomenclature: Imazethapyr; barnyardgrass, Echinochloa crus-galli (L.) Beauv. #3 ECHCG; red rice, Oryza sativa L. # ORYSA; Sesbania exaltata (Raf.) Rydb. Ex A. W. Hill # SEBEX.
Additional index words: Imidazolinone herbicides, rice.
Abbreviations: POST, postemergence; PPI, preplant incorporated; WAT, weeks after treatment.
