Effectiveness of atrazine on populations of capim navalha and selectivity of two varieties of pastagem

Abstract

Paspalum virgatum L. is a grass weed common in pasture and has difficult control, mainly due to its similarity to forage. Conventional techniques such as grazing and replanting of pasture have been unsatisfactory in the control of this weed. The objective of this work was to evaluate the control of the razor-blade grass (P. virgatum L.) at the pre-emergence atrazine, by means of a dose‑response curve and the selectivity of this herbicide in the pastures of Brachiaria brizantha cv. Marandu and Panicum maximum cv. Mombasa. Three independent experiments were carried out with each species on two types of soils (Dystrophic Yellow Red Latosol - LVAd with loamy clay texture and Dystrophic Yellow Red Argisol - loamy texture PVAd), using the percentage grading scale to verify the control of the and herbage phytotoxicity and dry mass at the end of the experiments. Atrazine controlled the razor blade from 15 days after application (DAA) at doses below the manufacturer’s recommendation (250 and 500 g ha-1 i.a.). However, despite the phytotoxicity symptoms caused by atrazine, there was a resumption of growth at 60 DAA for both B. brizantha cv. Marandu and P. maximum cv. Mombasa. There was less phytotoxicity to pastures in the soil of loamy clay texture than the loamy texture soil. The atrazine provided efficient control of P. virgatum L. (500 g ha-1 i.a.) when applied in pre-emergence and selectivity to B. brizantha cv. Marandu (<2,000 g ha-1 i.a.) and P. maximum cv. Mombasa (<500 g ha-1 i.a.).