Interaction of clethodim with glyphosate and/or 2,4-d at different doses and spray volumes in the control of glyphosate-resistant ryegrass

Background: Ryegrass is considered an important weed in crops in the state of Rio Grande do Sul, Brazil, for being resistant to the herbicide glyphosate. Objective: This study evaluates ryegrass control by applying different spray volumes and doses of clethodim alone or in combination with glyphosate and/or 2,4-D. Methods: Two field experiments were conducted in a 5 x 3 factorial design. In experiment I, factor A consisted of clethodim (96 g a.i. ha(-1)); clethodim (96 g a.i. ha(-1)) + glyphosate (1,080 g a.e. ha(-1)); clethodim (96 g a.i. ha(-1)) + 2,4-D ( 1,047 g a.e. ha(-1)); clethodim (96 g a.i. ha(-1)) + glyphosate (1,080 g a.e. ha(-1)) + 2,4-D (1,047 g a.e. ha(-1)); and control without treatment. Factor B consisted of three spray volumes (40, 80, and 120 L ha(-1)). In the second experiment, factor A consisted of the same herbicides and their associations aforementioned and factor B consisted of three increasing doses of the herbicide clethodim (96, 192 and 288 g a.i. ha(-1)). The herbicides were applied at the milky stage of ryegrass grains. Ryegrass control at 10, 20, and 30 days after application (DAA) of herbicides and dry matter were evaluated. Results: Spray volume reduction did not interfere with ryegrass control by clethodim and glyphosate or clethodim, glyphosate, and 2,4-D at 30 DAA, but it did interfere with the application of clethodim alone or associated only with 2,4-D. Doses above 192 g a.i. ha(-1) of clethodim alone or in mixture were efficient for ryegrass control. Conclusions: Greater clethodim doses and spray volume increased control of ryegrass at the milky grain stage and decreased the antagonism in the associations with 2,4-D.