Efeito de diferentes programas de aplicação de fungicidas sobre cultivares de soja com e sem resistência genética a Phakopsora pachyrhizi

Abstract

Soybean is one of the main oleaginous plants produced and consumed in the world, however, the crop is subject to a number of factors that may compromise the expression of its productive potential, among them the Asian rust of soybean caused by Phakopsora pachyrhizi. For the control of this disease to be effective, the same must be done in order to integrate different actions among these the use of resistant cultivars and fungicides. Therefore, the objective of this work was to verify the influence of different fungicide application programs in a resistant soybean cultivar and another susceptible to asian rust, in the progression of the disease and on yield variables. The soybean cultivars TMG 7062 RR IPRO® (resistant) and BMX Tornado RR (susceptible) were planted in the experimental area at Universidade Federal da Fronteira Sul – campus Cerro Largo. The plants were submitted to different fungicide application programs: only one application in stage R1 (T1); two applications being one in the V13 stage and the other in the R2 stage (T2); three applications being one in the V10 stage, one in R2 and one in R5.1 (T3); four applications being one in V6, one in V15, one in R2 and one in R5.1 (T4). Severity assessment was performed on the different thirds of the plant separately to determine the area under the disease progress curve (AACPD), as well as evaluation of yield and defoliation. The highest AACPD was always reached by the susceptible cultivar, in all thirds of the evaluated plant. In the AACPD of the middle and lower thirds as well as the percentage of defoliation and in the mass of a thousand grains, in both cultivars, it was observed an effect of the increase of the number of fungicide applications on these observed variables. As for productivity, in both cultivars, there was no increase in productivity, while the number of fungicide applications increased.