Tolerância e respostas fisiológicas do feijão-caupi a herbicidas aplicados em pós-emergência

Abstract

The present study was conducted in the experimental area of the Institute of Agronomy of the Federal Rural University of Rio de Janeiro, Seropédica, RJ, Brazil, in order to evaluate the tolerance and physiological responses of cowpea, submitted to herbicides with different mechanisms of action . The treatments consisted of the herbicides Bentazon (720 g ha-1), Fluazifop-p-butyl (187.5 g ha-1), Fomesafen (250 g ha-1), Fluazifop-p-butyl and Fomesafen G ha-1 + 250 g ha-1) and two controls without herbicide, one with and without no weeding, arranged in a randomized complete block design with four replications. The plots consisted of 5 planting lines, spaced 0.5 m apart and 5 m long. The application of the herbicides was done with a CO2 pressure pressurized sprayer, working at a pressure of 250 kPa, equipped with four tips TT 110.02 applying a volume of syrup of 240 liters per hectare and was realized with the bean plants of cowpea in stage Vegetative V3. The weed population was evaluated one day before and 30 days after herbicide application (DAA). Foliar protein content was evaluated at 3, 5, 7, 14, 21 and 28 DAA. Phytotoxicity and weed control efficiency were evaluated at 7, 14, 21 and 28 DAA. The maximum quantum yield of photosystem II (Fv / Fm) and the effective quantum yield of photosystem II (ΦFSII), photochemical quenching (qp) and non-photochemical quenching (qn and NPQ) were evaluated after application on the subsequent six days and 14, 21, and 28 DAA. Measurements were performed at 4:00 p.m. and 7:00 p.m. for Fv / Fm and at 10:00 p.m. for ΦFSII, qp, qn and NPQ. The leaf area and dry mass of cowpea plants were evaluated in pre-flowering. The productivity was evaluated by harvesting 10 plants in the useful area of each treatment. Data, except for phytosociology, were submitted to analysis of variance and when it was found significant, a comparison was made between the Tukey test at 5% probability. There was a change in the weed flora, in which before the application, the species were distributed homogeneously, with a predominance of Panicun maximum and Oxalis latifolia. After application of the herbicides, Oxalis latifolia was the only species present in all treatments. Fomesafen showed to be phytotoxic to cowpea, causing a reduction in leaf protein content as well as in the dry mass of the crop plants when applied alone or in mixture with Fluazifop-p-butyl. The fomesafen and Fluazifop-p-butyl mixture was efficient in controlling weeds, not causing productivity reductions. Bentazon was the herbicide that most affected the physiological parameters, decreasing the photosynthetic yield of the plants, by acting directly on the electron transport. It was concluded that the Fomesafen and Fluazifop-p-butyl mixture provided good weed control. The method of quantification of chlorophyll a fluorescence emission was not efficient to measure the physiological effects of the application of the herbicides Fluazifop-p-butyl and Fomesafen