Abstract
ABSTRACT Evolution has been reported for the reduction in Phakopsora pachyrhizi sensitivity to the mixtures of the three site-specific mechanisms of action (DMIs, QoIs and SDHIs) used in its control. The aim of this study was to quantify the current contribution of QoIs, alone or in mixture with triazoles, in the control of Asian soybean rust. In an experiment carried out in the field, the efficacy of quinone outside inhibitors (QoIs), or strobilurins, was compared for Asian soybean rust control. The isolated effects of four doses of azoxystrobin, picoxystrobin, pyraclostrobin and trifloxystrobin were evaluated, as well as of four applications during the crop cycle. Control by commercial mixtures of these QoIs with triazoles was also compared. Severity was evaluated in four phenological stages, and control was calculated based on final severity data, area under rust progress curve, defoliation, one-thousand-grain mass, grain yield and damage caused by the disease. The lowest mean of rust control efficacy resulted from applications of azoxystrobin (15.8 and 11.19%) and pyraclostrobin (15.4 and 16.76%) and the highest mean was found for picoxystrobin (54.1 and 54.35 %) and trifloxystrobin (69.7 and 64.46%), calculated based on final severity and AUDPC, respectively. Such efficacy is not enough to cover the fungicide application cost, although there was a positive effect of treatments on disease control and grain yield.
Highlights
Tem sido relatada a evolução da redução da sensibilidade de Phakopsora pachyrhizi às misturas dos três mecanismos de ação sítio-específicos (IDMs, IQes e ISDHs) usadas no seu controle
Considering the diseases that affect soybean, the greatest damage is due to Asian soybean rust (ASR), caused by the Basidiomycete fungus Phakopsora pachyrhizi Sydow & Sydow [16], which was detected in South America in 2001 [7]
ASR control measures include sowing early maturing cultivars at the beginning of the recommended season, growing cultivars with partial resistance to rust, observing the soybean-free period, eliminating volunteer plants and applying fungicides in the foliage when the disease is detected in the region [13]
Summary
Tem sido relatada a evolução da redução da sensibilidade de Phakopsora pachyrhizi às misturas dos três mecanismos de ação sítio-específicos (IDMs, IQes e ISDHs) usadas no seu controle. From the 2005/06 season, based on producers’ complaints of control failure and on scientific reports [8, 15], double mixtures of site-specific fungicides DMIs + QoIs (azoxystrobin + cyproconazole and pyraclostrobin + epoxiconazole), endorsed by FRAC [3] as an anti-resistance strategy, started to be used. In the 2014/15 soybean crop, ASR control was done by spraying fungicide mixture containing SDHI (benzovindiflupyr + azoxystrobin), which had an efficiency greater than 90%.
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