Economic threshold of smooth pigweed escaped from a herbicide program in roundup ready® soybean

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.