Interferência de fatores morfoambientais e horários de aplicação de fluazifop-p-butyl e fomesafen no controle de infestantes, seletividade e lucratividade da cultura do feijoeiro (Phaseolus vulgaris L.)

Abstract

The weeds compete with the cultivated crops and among the negative effects of this interaction is the reduction of the crop yields. The chemical method is the main weed control technic in the common bean crop (Phaseolus vulgaris L.). The efficacy of the herbicides depends on a number of factors, including: environmental conditions (in function of the time of application) at the moment of spraying of the herbicide and doses used. A research program was developed on the Agronomy course of UTFPR, Pato Branco, PR, during the 2010-11 with the main objectives to evaluate the impact of the application time (and therefore environmental variables) and doses of fluazifop-p-butyl and fomesafen on the: performance of these herbicides in the control of mono and dicotyledonous weeds, respectively; selectivity of bean crop to fomesafen; and the lucrativity of the common bean crop. The environmental variables, according to the time of day or season of year in which herbicides were applied, influence the control of weeds. Fluazifop-p-butyl activity has been favored when sprayed at 06:00h. The relative humidity and grass leaf angle were the factors most important affecting this herbicide performance. For this same compound, night application has been effective to mitigate the negative effects of the afternoon application. The performance of fomesafen to control broadleaf weeds has been maximum when the product was sprayed at 11:00h and 16:00h. In this case, the irradiance and the air temperature have been the main factors to affect the herbicide efficacy. The doses of fluazifop-p-butyl + fomesafen which allowed best weed control have increased grain yield and profitability of the common bean crop production. In some cases, the maximum net return has been obtained with a dose lower than that needed for maximum herbicide efficacy. Fomesafen has injured the common bean plants, but they have recovered with time. The degree of phytointoxication has increased at high fomesafen doses and when it has been sprayed at 11:00h and 16:00h. During these times, the air temperature and irradiance were the highest. It can be summarized that the efficacy on weed control and on the common bean injury was dependent on the herbicide used, on the environmental conditions during the time of the herbicide spray, and on the rates applied. The selection of the correct time of the day and rate of application can optimize the weed control, can reduce the crop yield losses due to competition, and can optimize the crop profitability.