Abstract
At maximum vegetative growth, sprays with fungicide to control Asian rust (Phakopsora pachyrhizi Sydow and P. Sydow) should reach high canopy penetration and plant coverage. Therefore, the central objective of this study was to determine leaf area, spray deposition, and plant coverage by fungicides sprayed on soybeans as a function of sowing seasons and plant population densities with reduced doses of tebuconazole and azoxystrobin + cyproconazole. Field experiments were conducted in the 2009/2010 and 2010/2011 crop years, using a medium-cycle soybean cultivar MG/BR–46 (Conquista) under a natural infestation of Asian soybean rust. Leaf area (LA) and leaf area index (LAI) were measured at three developmental stages (V8, R2, and R4). Spray deposition and coverage were evaluated during the first fungicide spraying. As results, LAI decreased as plant population decreased. Despite the lower LAIs, smaller plant populations had no effect on spray deposition and plant coverage. Both fungicides presented similar depositions on all thirds when plants had lower development.
Highlights
Soybean (Glycine max (L.) Merrill) is worldwide characterized as an agricultural product of great economic importance
Leaf areas (LAs) at R2 and R4 reproductive stages were larger in the smaller plant densities
leaf area index (LAI) decreased as plant population reduced when considering the same stages and V8 (Table 1)
Summary
Soybean (Glycine max (L.) Merrill) is worldwide characterized as an agricultural product of great economic importance. The production of these beans has faced several challenges to reach high quality and productivity such as attaining an effective control of pests and mainly leaf diseases caused by fungi, which normally require two or three fungicide applications (CUNHA et al, 2011). Asian soybean rust is a highly aggressive disease caused by the fungus Phakopsora pachyrhizi According to Santos et al (2007) and Seixas et al (2006), Asian soybean rust is mainly controlled by fungicide spraying. Asian rust symptoms begin in the lower third of plants; fungicide applications must cross the barrier imposed by leaves and promote good coverage inside plant canopies (ZHU et al, 2008)
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