Critério para tomada de decisão de controle de plantas voluntárias de milho infestantes da soja

Abstract

Volunteer plants of genetically modified (GM) maize, especially resistant to herbicides, have currently become weeds, infesting subsequent crops, causing high competitiveness and, as a consequence, losses in grain yield. Therefore, the objective of this work was to evaluate the competitive ability and the level of economic damage in soybean cultivars infested by volunteer and genetically modified (GM) maize plants. The experiment was conducted in the field, in a completely randomized design, with one repetition. The treatments consisted of soybean cultivars (Nidera 5909 RG; Brasmax Elite IPRO; Syngenta 13561 IPRO; Dom Mario 5958 RSF IPRO; Nidera 6909 IPRO; Brasmax Lança IPRO) and 12 voluntary maize densities (hybrid Syngenta 488 Vip 3) predicted for each cultivar, ranging from 0 to a maximum of 130 plants m-2. At 30 days after emergence, the quantification of plant density (DP), soil cover (CS), leaf area (AF) and shoot dry mass (MS) of volunteer maize plants. In soybean, grain yield, control cost, price of a soybean bag and control efficiency were determined. A rectangular hyperbola was efficient to estimate the grain productivity losses of soybean cultivars due to voluntary maize interference, with MS being the variable that presented the best fit to the model. The soybean cultivars Nidera 5909 RG, Syngenta 13561 IPRO and Brasmax Lança IPRO show greater competitive ability and NDE values of 0.07 to 0.20 plants m-2 in the presence of volunteer maize. The lowest NDE values ranged from 0.02 to 0.12 plants m-2, for the cultivars Dom Mario 5958 RSF IPRO, Nidera 6909 IPRO and Brasmax Lança IPRO, with these being assessed as having the lowest competitiveness. NDEs decreased with the increase in grain productivity, price of a soybean bag, the efficiency of the herbicide and the reduction in the cost of controlling voluntary maize, thus, justifying the adoption of control measures even at lower densities of the weed.