Molhamento foliar após a aplicação de fungicidas no controle da ferrugem asiática da soja

Abstract

Asian soy rust caused by the fungus (Phakopsora pachyrhizi) is one of the main causes of reduced productivity in soybeans worldwide, and chemical control is the most efficient way to minimize disease damage. The occurrence of rain after the application of fungicides is one of the main causes of loss of efficiency of the chemical products, either by runoff, transport of the active ingredient to other parts of the plant or to the soil, and also, dilution of the product. Therefore, it was the objective of this work to evaluate the effect of the occurrence of artificial rainfall after the application of fungicides in the control of Asian rust (Phakopsora pachyrhizi) and soybean yield. The experiment was conducted during the 2016/2017 harvest, in the property of Mário Seibt, located in the interior of the municipality of Cândido Godói, in the northwestern region of the state of Rio Grande do Sul. The experiment was conducted in a 4x5 factorial (four applications in which the simulated rain occurred x five times after the application in which the precipitation simulation was performed) with four replications. The design was a randomized block design. The applications in which the simulated precipitation occurred were the first application, second application, third application of fungicides and in none of the applications (control). The times after application of fungicide in which precipitation occurred were zero hours, half an hour, one hour, two hours and four hours after application of fungicides. Rust severity assessments were performed throughout the reproductive phase of the crop, defoliation at the R6 stage, height of the first pod insertion, and productivity. There was no interaction between the time factors of the occurrence of simulated precipitation and the application in which precipitation occurred. Also, it was not possible to observe a significant difference between the times of precipitation occurrence after the application of fungicides to none of the observed variables. Regarding the application in which the simulated precipitation occurred, only the variables defoliation in the R6 stage and height of insertion of the first pod presented statistical difference.