Abstract
Asian soybean rust (ASR) caused by Phakopsora pachyrhizi since it was first reported in Brazil in 2001 has been subject of studies regarding the use of fungicides to its control. Low efficiency of triazol (demethylator inhibitors-DMI’s) or stobilurin (quinone outside inhibitor-QoI’s) has been reported on the control of ASR under field conditons. For this reason experiments were conducted to study the effects of these systemic fungicides associate with protectant multi-site fungicides (MSF) on ASR control preventively and at the onset of the epidemic. All combinations of fungicides were effective to control ASR and promoted greater soybean yield gain compared to the control. The analysis of the efficacy of ASR control in the lower, medium and upper part of the plant canopy, showed that application of Epoxiconazole + Pyraclostrobin and Cyproconazole + Azoxystrobin reduced ASR and leaf fall (%), and increased soybean yield grain. The severity of the disease increased from the lower to the upper part of the plant. The application of DMI+ QoI associated with MSF applyed when disease severity reached 2%, promoted effective reduction of ASR, increased yield and reduced leaf fall. Overal the DMI’s + QoI’s associated with MSF was 68% and 70.2% more efficient on ASR control and soybean grain yield, respectively than the control. Mancozeb and Chlorothalonil associated with the lowest dose of Epoxiconazol + Pyraclostrobin (10.2 + 33.2 g.a.i./ha) or Cyproconazole + Azoxystrobin (12.5 + 30.0 g.a.i./ha), respectively increased soybean grain yield at least 45.0%; the same combinations of the fungicides Epoxiconazol + Pyraclostrobin (15.3 + 49.8 g.a.i./ha) and Cyproconazole + Azoxystrobin (25.0 + 60.0 g.a.i./ha) 50% less than the commercial dose, increased 89.5% and 109.0%, respectively. The use of high risk (DMI and QoI) fungicides combined to low risk (MSF) applyied properly, can be a new strategy for the management of ASR at short and long term, even after the epidemics has reached 2.0% severity. Furthermore, due to the residual effect, MSF can promote higher longevity of DMI and QoI molecules.
Highlights
Among all diseases affecting soybean, Asian soybean rust (ASR) caused by the fungus Phakopsora pachyrhizi
The results of the effect of doses of Epoxiconazle + Pyraclostrobin associated with multi-site fungicides (Mancozeb, Chlorothalonil and Metiram) to control ASR and on grain yield are presented in Figures 1 and 2, respectively
The reason to include multi-site fungicides (MSF)’s in mixture with demethylation inhibitors” (DMI) and QoI fungicides is due to the fact that several researchers reported that the formulations involving triazol + strobilurin have been failed on the control of ASR (Godoy et al, 2015, 2016)
Summary
Among all diseases affecting soybean, Asian soybean rust (ASR) caused by the fungus Phakopsora pachyrhizi The fungi is considered highly aggressive, causing damages varying from 10 to 90% in soybean fields in Asian (Sinclair & Hartman, 1999) and yield losses ranging from 10 to 80% in some growing regions in South America (Navarini et al, 2007). The first symptoms of ASR begin as very small brown or brick-red spots on leaves, grouped into tanned coloring lesions (2-5 mm in diameter) develop into a pustule (uredinia) where an abundant sporulation produced, help the fungus dissemination (Bromfield, 1984) In the field, these spots usually begin in the lower canopy at or after flowering, jas.ccsenet.org
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