Flumioxazina isolada e em associações no controle de plantas daninhas e sua dinâmica em palha, textura de solo e simulação de lâminas d’água

Abstract

Mechanized sugarcane harvesting can influence the weed population and modify the chemical and biological characteristics of the soil. The residual straw on the surface may hinder the penetration of pre-emergent herbicides, affecting control efficacy. In this scenario, the use of pre-emergent herbicides, combined with different molecules, becomes essential to optimize weed management. The dynamics of herbicide action are influenced by the amount of straw, soil texture, and water sheets (intervals before the first rain), factors that affect the transposition and persistence of the product in the soil. The objectives of the study were: i) To identify the interactions and effects of herbicides applied in combination with flumioxazin for controlling the main weeds present in sugarcane crops; ii) To analyze the persistence of flumioxazin in different soil textures; iii) To evaluate the influence of the amount of sugarcane straw and the intervals before the first rain on the efficacy and persistence of the product. The study was divided into two stages, with both experiments conducted in a greenhouse in a completely randomized design with four replications. In the first stage, six experiments were conducted (one for each weed species), using the following weeds: Rottboellia cochinchinensis (Loureiro) W.D. Clayton, Urochloa decumbens (Stapf) R.D. Webster, Digitaria horizontalis (Willdenow), Merremia aegyptia (Linnaeus) Urban, Merremia cissoides (Lamarck) A.R. Simões & Staples, and Ipomoea triloba (Linnaeus) var. genuina (Meisner). The experiments were organized in a factorial scheme of 8 x 5, with factor A consisting of 8 herbicide treatments (flumioxazin alone and in combination with ametryn, diclosulam, imazapic, isoxaflutole, metribuzin, metsulfuron-methyl, and S-metolachlor) and factor B consisting of 5 intervals between herbicide application and weed seeding (0, 10, 30, 40, and 60 days). In the second stage, two experiments were set up, one in medium-textured soil and another in clayey soil, using I. triloba as the weed species. The experiments were organized in a 9 x 2 factorial scheme, with factor A consisting of 9 treatments simulating the intervals between herbicide application and weed seeding, with and without simulated rainfall (0, 15, 30, 40, and 60 days, 15 days without rain, rain simulation followed by 15 more days without rain, repeating the same intervals for 30, 40, and 60 days). Factor B consisted of two treatments, representing the amount of sugarcane straw on the soil surface (0 and 10 t ha-1). Additionally, untreated controls were included, with and without straw. In both stages, the variables evaluated were weed control (%) and reduction of dry shoot biomass of the species. The combination of flumioxazin with other herbicides provided efficient control (>90%) of the evaluated species up to 10 days after application (DAA). The combination of flumioxazin + metribuzin maintained satisfactory control up to 60 DAA for I. triloba, M. aegyptia, M. cissoides, D. horizontalis, and R. cochinchinensis, and up to 40 DAA for U. decumbens. All treatments reduced the dry shoot biomass of R. cochinchinensis by more than 90%. In medium-textured soils, flumioxazin had residual activity of up to 60 days for controlling I. triloba without straw, regardless of precipitation. With 10 t ha-1 of straw, the residual activity varied between 55 and 60 days, with or without rain. In clayey soils without straw, residual activity was less than 40 days without rain and 55 days with precipitation. In the presence of 10 t ha-1 of straw, control was maintained for up to 60 days without rain and 75 days with precipitation. The combination of flumioxazin with other herbicides increases the residual period and improves weed control efficacy. In clayey soils, flumioxazin shows greater variation in response depending on the presence or absence of straw and precipitation.