Tolerance of nine rice varieties to clomazone at 1.12 kg ai/ha was evaluated from 2000 to 2002. Rice injury was 27 to 51% at 14 d after treatment (DAT) and reduced to 5 to 30% at 42 DAT with long-grain ‘Drew’ having less injury compared with all medium-grain varieties. Medium- grain ‘Earl’ and ‘LL-401’ were injured most compared with all other varieties at 42 DAT. Plant height was reduced by clomazone with all varieties except Drew at 34 DAT. Clomazone also reduced plant population of Earl, LL-401, and ‘Wells’, but other varieties were not affected at 34 DAT. However, rice grain yield reduction was only observed with LL-401. These results indicate that differential tolerance to clomazone exists among rice varieties.

Nomenclature: Clomazone; rice, Oryza sativa L. ‘Bengal’, ‘Cocodrie’, ‘Cypress’, ‘Drew’, ‘Earl’, ‘CL-141’, ‘LL-401’, ‘LL-601’, ‘Wells’.

Additional index words: Herbicide tolerance.

Abbreviations: DAT, days after treatment; DPRE, delayed preemergence; PPI, preplant incorporated; PRE, preemergence.