Selectivity and weed control efficacy of pre- and post-emergence applications of clomazone in Southern Brazil

• PRE versus POST clomazone application resulted in transient injuries and no effects on rice yield.
• Direct correlation between rate and injury.
• Key factor > early Echinochloa crus-galli control.

During the 2006/07 and 2008/09 growing seasons in Southern Brazil, we evaluated crop selectivity and weed control efficacy of clomazone on rice when applied alone or in a mixture with other pre- and post-emergence herbicides (BRS Querência variety). All herbicide treatments caused some degree of rice injury during both years; however, in no case was the injury still visible 21 days after application. Rice injuries were observed when application rates exceeded the recommended dose, and particularly when the herbicide was applied pre-emergence. Density reduction and panicle sterility served as measures of rice injury. Echinochloa crus-galli was the primary weed; it reduced rice yields by approximately 50% compared treated plots. In both growing seasons, clomazone herbicide (400 g ai ha−1) controlled the weed 87.0%–99.6%, and it provided 8.06 t ha−1 to 9.44 t ha−1 of rice yield.