Abstract
Product deposition and foliar surface cover are highly impacting factors on the efficiency of foliar fungicides applied to soybean cultivars, due to their low mobility, with side effects on Asian soybean rust (ASR) control. Spray bar support systems, such as the air curtain (Vortex®) and the use of nozzles along the bar (Dropleg®), stand out as an alternative to obtain a better distribution of fungicide throughout the plant. In this study, two spray bar support systems (Vortex® and Dropleg®) were, therefore, evaluated and compared with the conventional spraying method based on the biological efficacy in ASR control. In order to do this, two harvests, with three spacing between rows and two cultivars were employed. Vortex® and Dropleg® spray bar support mechanisms do not effectively contribute to the optimization of Asian soybean rust control or to the grain crop yield, regardless of cultivar and row spacing. Decreasing the row spacing did not influence the level of control of Asian soybean rust, as the highest grain yield was obtained with the smallest spacing. The cultivar with genetic resistance to Asian rust showed lower levels of this disease, thus, greater control against the use of fungicides.
Highlights
The Phakopsora pachyrhizi and Glycine max pathosystem stands out as one of the most important limiting factor of oilseed productivity, due to the occurrence of the fungus in all countries where soybeans are grown, as well as the potential damage, ranging from 10 to 90% (Reis et al, 2012, Dalla Lana et al, 2015), the cultivar and the intensity of Asian rust (ASR) (Danelli et al, 2015)
In the 2013/2014 season of the SYN 1363 RR cultivar, the ASR severity in the plots with no fungicide application reached 77% and in the 2014/2015 harvest it was of 55.6%, as a result from the late implantation of crop and early start of the epidemic
In the ASR-resistant cultivar (Table 3), the severity of the disease was close to 10% and disease control was higher than 90%
Summary
The Phakopsora pachyrhizi and Glycine max pathosystem stands out as one of the most important limiting factor of oilseed productivity, due to the occurrence of the fungus in all countries where soybeans are grown, as well as the potential damage, ranging from 10 to 90% (Reis et al, 2012, Dalla Lana et al, 2015), the cultivar and the intensity of Asian rust (ASR) (Danelli et al, 2015) As a result, these losses, estimated at 21 billion US dollars, between 2002 and 2013, directly and indirect impacting the Brazilian economy (Godoy et al, 2016). Low distance of the earlier rows favors disease development as it may generate bad circulation of air, increase in relative humidity and prolongation of leaf surface wetting (Reis et al, 2012)
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