Número de aplicações de fungicidas sobre o progresso de mancha-alvo em cultivares de soja

Abstract

Target spot (Corynespora cassiicola) has become a problematic disease for soybean crops, and control recommendations include chemical treatment with fungicides from the group of strobilurins, carboxamides and triazoles associated with multisite fungicides, as well as the use of cultivars that have higher levels of resistance against the disease. The objective was to evaluate the progression of target spot in an area with Corynespora cassiicola inoculation against two soybean cultivars and the number of applications of systemic fungicides associated with multisite and their effects on crop yield. The experiment was carried out in the Experimental Area and in the Plant Pathology Laboratory of the Universidade Federal da Fronteira Sul - Campus Erechim, in the 2022/23 crop season. The experimental design used was randomized blocks, in subdivided plots, with four replications. Two soybean cultivars (BMX Garra IPRO and DM 57i52 IPRO) were used in the plots; and fungicide applications (T1 - control, without application; T2 - two; T3 - three; and T4 - four applications) in the subplots. Progress (AUDPC) and daily increase (%) of target spot were evaluated; defoliation (%); number of pods per plant (NPP) and grains per plant (NGP); thousand grains weight (TGW, g); and productivity (kg ha-1 ) were evaluated. The results showed that the use of three fungicide applications reduces the progress of the target spot in both soybean cultivars and defoliation is less intense in the treatment with four fungicide applications (51.6%, BMX Garra IPRO; and 90.9%, DM 57i52 IPRO). The cv. DM 57i52 IPRO is more resistant to target spot, which is supported by lower AUDPC (36.8) and lower daily disease rise. Consequently, this cultivar produced 9.4 sc ha-1 more than BMX Garra IPRO, under the growing conditions of the present study. The T4 treatment, containing two sequential applications of mancozeb (in R3 and R5- R6), combined with bixafem + prothioconazole + trifloxystrobin, provides greater TGW and productivity for the cvs. BMX Garra IPRO and DM 57i52 IPRO, in an environment with Corynespora cassiicola inoculation.