A study was conducted during 2005 and 2006 to evaluate the response of 10 rice cultivars to penoxsulam applied at 70 g a.i./ha to two- to three-leaf rice. A related study was conducted in 2004 and 2005 to compare the rice response to applications of penoxsulam at 35 and 70 g/ha and bispyribac-sodium at 28 g a.i./ha. In the first study, all 10 rice cultivars exhibited tolerance to penoxsulam as evidenced by plant height, number of days to 50 heading, and rice grain yield. In the second study, applications of both rates of penoxsulam and bispyribac-sodium reduced mass of rice roots by 65 to 71 at 2 weeks after treatment compared with a nontreated control. However, rice grain yield was higher following application of penoxsulam at 70 g/ha compared with yield of the nontreated control or yield following penoxsulam at 35 g/ha and bispyribac-sodium. Rice recovered from injury observed following herbicide application with no negative impact on grain yield. The results indicate that, although rice root injury can be severe following application, penoxsulam is safe for application to rice cultivars currently grown in the southern U.S. Rice Belt.
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