Abstract

This study aimed to evaluate the selectivity of the acetolactate synthase (ALS) inhibitor recommended herbicides for upland rice cultivars on different developmental stages. The experiment was conducted in the field, in Nova Xavantina-MT, Mato Grosso, Brazil, from season 2009/2010. The experimental design was the one of randomized blocks in factorial scheme, composed by the herbicide treatments penoxsulam (36 g ha^-1); bispyribac-sodium (50 g ha^-1); pyrazosulfuron-ethyl (20 g ha^-1) and weeded control. Herbicides were applied at three times: 15, 30 and 45 days after emergence (DAE) with four replications in two upland rice cultivars: BRS Pepita and BRS Monarca. At 7, 14 and 28 days after application (DAA) the following assessments were performed: phytotoxicity to the crop, plant height, dry weight, number of panicles m^-2, grains per panicle^-1 and productivity. The highest levels of phytotoxicity were observed in plants treated with bispyribac-sodium applied at 15 and 30 DAE. The rice plants were able to recover as for height influenced by herbicides from 14 DAA. The dry weight of plants was not affected by herbicide application. Since they have not reduced the grain productivity, the herbicides tested, when applied at 30 DAE, have showed their potential to be used only in BRS Monarca cultivar.

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