Field experiments were conducted in 1999 and 2000 at the Rice Research and Extension Center at Stuttgart, AR, on a DeWitt silt loam and at the Pine Tree Branch Experiment Station near Colt, AR, on a Calloway silt loam to evaluate the tolerance of 14 rice cultivars and four experimental cultivar lines to clomazone at 0.34 and 0.67 kg ai/ha applied preemergence. Early-season chlorosis 14 days after emergence (DAE) ranged from 1 to 21% in 1999 and 3 to 40% in 2000 when averaged over herbicide rate. The experimental cultivar line RU961096 was slightly more susceptible to clomazone than other cultivars and lines. However, RU9701041 was more tolerant to clomazone at 0.67 kg/ha 14 DAE than other cultivars and lines. By 28 DAE, all cultivars had <13% chlorosis in 1999 and <8% in 2000. The experimental cultivar line RU9601096 and cultivar Koshihikari did not recover as quickly as the other 16 cultivars and cultivar lines. Early-season chlorosis had no effect on days to 50% heading or yield for any of the cultivars evaluated.

Nomenclature: Clomazone; rice, Oryza sativa L. ‘Ahrent’, ‘Bengal’, ‘Cocodrie’, ‘Cypress’, ‘Drew’, ‘Jefferson’, ‘Kaybonnet’, ‘Koshihikari’, ‘Lemont’, ‘LaGrue’, ‘Madison’, ‘Mars’, ‘Priscilla’, ‘RU9601096’, ‘RU9701041’, ‘RU9801081’, ‘RU9801148’, and ‘Wells’.

Additional index words: Rice cultivar tolerance, rice injury.

Abbreviations: DAE, days after emergence; PPI, preplant incorporated; PRE, preemergence.