Spray Mixture Volume in the Control of Asian Soybean Rust

While soybean is one of the main crops produced in Brazil, it can have severe losses of production due to the incidence of Asian rust caused by the fungus Phakopsora pachyrhizi. Fungicide application is the main method of rust control. In order to reduce application costs, there has been a trend to reduce spray volumes. The purpose of this study was to evaluate the effectiveness of applying the commercial mixture trifloxystrobin + prothioconazole (Fox (R)) in different spray mixture volumes on the leaves of the lower, middle and upper thirds of soybean plants. Rust control and yield were evaluated under high disease pressure. The spray volumes evaluated were: 50 L ha-1, 100 L ha-1, 150 L ha-1, 200 L ha-1, 300 L ha-1 and 400 L ha-1 in three fungicide applications at the R1, R4 and R5.5 stages using the TT 11001 tip from Teejet (R) at a working pressure of 5 bar. There was a direct relationship between the increase in spray volume and spray coverage levels in the upper, middle and lower thirds of soybean plants. The increase in spray volume provided greater leaf coverage but had no effect on rust control or yield. The commercial mixture trifloxystrobin + prothioconazole (Fox (R)) can control rust at spray volumes of 50 L ha-1 under favorable environmental conditions.