The main phytosanitary problem related to soybean in Brazil is Asian soybean rust. Fungicide use is an effective measure to control this disease. Substances added to the solution, such as adjuvants, can influence the fungicide efficacy. In the crop seasons 2008/09 and 2009/10, we tested the effect of six adjuvants (Assist®, Aureo®, Break Thru®, Joint®, Natur'l Oil® and Silwet®) added to picoxystrobin+cyproconazole, besides a control (without fungicide) and a standard control (Nimbus®), totaling eight treatments. For the disease evaluation, leaflets were collected from the upper, medium and lower thirds of the crop, and the number of lesions and uredinia per leaflet was observed in the three central lines of each plot, in addition to the disease incidence. In the 2009/10 crop season, during the second spraying, hydro-sensitive papers were used to evaluate the volumetric median diameter (VMD), the number median diameter (NMD), the coefficient of variation of droplets (CV), the density of droplets, the recovered volume (L ha-1) and the area covered by the fungicide solution (%). In both crop seasons, there was no effect of the tested adjuvants on the disease control efficiency compared to the standard control (fungicide + Nimbus®), which indicates that they can be used as an alternative. In the 2009/10 crop season, the adjuvant Aureo® provided the lowest values of VMD, NMD, CV, recovered volume and covered area, while the treatments providing the highest values were Assist, Joint, Nimbus and Silwet. No symptoms of phytotoxicity were observed associated with the addition of any tested adjuvant.
Glycine max; Phakopsora pachyrhizi; surfactants
