Selectivity of atrazine to forage grasses through dose-response curve

Seletividade de atrazine a gramíneas forrageiras através de curva dose-resposta

Resumo

This research aimed to evaluate the selectivity of atrazine applied in forage pre-emergence: Panicum maximum cv. Massai, Panicum maximum cv. Zuri and Panicum maximum cv. Tamani and Brachiaria brizantha cv. BRS Piatã. A randomized block design was adopted, applying eight doses (8D, 4D, 2D, D, 1/2D, 1/4D, 1/8D and no dose, where D is the dose of atrazine 2,000 g ha^{- 1}) with four replications each, in plastic vases with a capacity of four liters. The evaluation was performed visually, with scores from 0 to 100, where 0 was considered absence of injuries and 100 the death of the plant at 15, 30 and 60 days after application (DAA) and dry mass at 60 DAA. For each experiment, the data were submitted to analysis of variance with application of the F test. When the F test was significant, the atrazine doses were adjusted to log-logistic non-linear regression models. It can be concluded that Panicum maximum cv. Massai shows phytotoxicity at a dose of 2,000 g ha^-1 with subsequent growth resumption at 30 and 60 DAA.