Deposição de fungicida em cultivares de soja com diferentes hábitos de crescimento, controle e sensibilidade de Phakopsora pachyrhizi a fungicidas

Abstract

In Brazil, the second largest soybean producer in the world, Asian soybean rust (ASR), caused by the fungus Phakopsora pachyrhizi, is the most destructive disease, with damages that can reach 75% of production. This study aimed to find the most effective fungicide application to control ASR, as well as, to determine the sensitivity of P. pachyrhizi to fungicides of commercial usage. In two field experiments, the effect of the usage, or not, of a curtain of chains added to the spray boom was evaluated on fungicides application in six different hours. The applications were performed at 6:00 and 9:00 am, 12:00, 3:00, 6:00 and 9:00 pm, thus allowing the investigation of possible effects of heliotropism on fungicide spray penetration. The experimental design was in randomized blocks. In the trial with the determinate growth cultivar, the usage of the curtain of chains increased droplet deposition within the plant canopy at all the tested times. Applications made at 6:00 am showed the greatest need for the curtain of chains. In the experiment conducted with the indeterminate growth cultivar, the usage of the curtain of chains increased droplet deposition only in the first hours of the day applications, which had dew present (6:00 and 9:00 am). Applications made at 6:00 and 9:00 pm without the addition to the bar, showed better control of incidence and uredias/cm2 than sprays made at the same times with the assisted bar. In both experiments, high grain yield results were obtained by sprays made at 12:00 and 3:00 pm, with or without the presence of the curtain of chains. In another part of the study conducted in laboratory, the inhibitory concentration (IC50) of eight commercial usage fungicides to P. pachyrhizi was quantified in vitro using isolates from three producing soybean regions: Passo Fundo (RS), Ponta Grossa (PR) and Primavera do Leste (MT). In a completely randomized block design experiment with four replications per treatment, Petri dishes containing two different substrate, agar-water or agar-leaf extract, received the fungicide solutions in different concentration. The pyraclostrobin and trifloxystrobin + prothioconazole mixture showed IC50 values lower than 1 mg/l for all the isolates, demonstrating high