Abstract Introduction A. hybridus interference in soybeans varies with population size and may be quantified by mathematical models that allow establishing the threshold levels. Objective Determine the interference of A. hybridus escaped from an herbicide program and with multiple resistance to EPSPs and ALS-inhibiting herbicides on soybean yield and its economic threshold (ET). Methods Two experiments were conducted in a randomized block design. The treatments consisted of populations of A. hybridus ranging from 0 to 41 plants m-2 (2018/19) and 0 to 32 plants m-2 (2019/20). The yield components and yield plant-1 of soybean were evaluated. The rectangular hyperbola model was fitted to the soybean yield loss. ET was calculated according to yield potential, price paid for grains, control cost and weed control efficiency Results The increase in populations of A. hybridus has decreased in the number of pods and grains-1 of soybean in both periods. The parameter i was 4.47 and 8.32%, and the ET ranged from 0.16 to 1.21 plants m-2 in 2018/19 and from 0.09 to 0.65 plants m-2 in 2019/20. Conclusions One A. hybridus m-2 may reduce 6.4% in the grain yield of soybean. ET occurs within the range of 0.09 to 1.21 plants m-2.

Abstract: 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.