Manejo de caruru-roxo (amaranthus hybridus) infestante de culturas agrícolas de verão

Abstract

Amaranthus genus plants are weeds of several crops of agronomic interest, causaing economic. Can cause reducing the quality of the harvested product. These species area considered aggressive when competing with crops due to have C4 photosynthetic cycle, wich high temperatures and water stress. Among them, A. hybridus stands out due to the presence of herbicide-resistant biotypes, has high seed production, rapid establishment, growth and development. In light of this, the objective of this work was evaluate herbicides efficacy when applied in pre and post-emergence, in addition to evaluate A. hybridus competitive ability when weed in corn, bean and soybean crops. In order to evaluate herbicide efficacy, applied in weed pre and post-emergence, it was installed 2 experiments in greenhouse, in randomized block design with four replications. In experiment I, it were used pre-emergent herbicides: diclosulam, imazethapyr, imazethapyr+flumioxazin, S-metolachlor, atrazine, [atrazine+simazine], metribuzin, flumioxazin, sulfentrazone, [sulfentrazone+diuron] and control, without herbicides. In experiment II, post-emergent herbicides were used: chlorimurom-ethyl, imazethapyr, mesotrione, glyphosate, diquat, metribuzin, atrazine, [mesotrione+atrazine], [atrazine+simazine], gluphosinate-ammonium, saflufenacil, carfentrazone, flumioxazin, fomesafen, 2,4-D choline e amine, dicamba and a control without herbicide application. Imazethapyr did no show good control, both when applied pre and post emergence, as well as dclosulam in pre-emergence and chlorimuron-ethyl in post emergence. Herbicides atrazine and [atrazine+simazine] showed good efficacy regardless application modality. Application of [imazethapyr+ flumioxazin], flumioxazin, sulfentrazone e [sulfentrazone+diuron] in pre-emergence showed the best results controlling until 60 days after application. Chlorimuron-ethyl and imazethapyr in post-emergence of A. hybridus did not showed satisfactory control effect. Experiments about the study of competitive ability of corn, bean and soybean in competition with A. hybridus were carried out in greenhouse, in proportion combinations of 100:0; 75:25; 50:50; 25:75 and 0:100% or 20:0, 15:5; 10:10; 5:15 and 0:20 plants per pot, crop versus weed. At 50 days after emergence, morphological variables such as height, leaf area and aerial part dry mass of the plants were determined, and, the physiological variables were determined to obtain the photosynthetic rate, stomatal conductance, transpiration, internal CO2 concentration, carboxylation efficiency, water use efficiency and chlorophyll content. The results obtained allow us to infer that A. hybridus competition interferes negatively in the morphological and physiological variables of corn, bean and soybean. Interspecific competition was more harmful to crops than intraspecific competition. Corn and bean showed better competitive ability in A. hybridus presence while soybean was more negatively affected. A. hybridus must be controlled even at low infestation densities in corn, bean and soybean as it causes negative effects on crop growth and development.