LAUSR

Abstract Adjuvant is a substance without phytosanitary properties, added to the spray carrier to increase the efficiency of application technology. Our objective was to determine the best option of combining fungicides and adjuvants to control soybean (Glycine max) leaf diseases, in three crops. The experiment was developed in the Campos Gerais region (PR - Brazil). The five treatments consisted of: 1) control (without fungicide application on soybean plants); 2) fungicide application on soybean plants without adjuvant; 3) fungicide with adjuvant based on mineral oil; 4) fungicide with adjuvant based on lecithin and 5) propionic acid and fungicide with 50% of the dose of adjuvant based on mineral oil + 50% of the dose of surfactant adjuvant based on lecithin and propionic acid. The analyzed variables were physicochemical characteristics of the spray carrier, incidence and severity of diseases and the yield components. A completely randomized design was used to study the physicochemical characteristics of the carrier and in randomized blocks for the field experiment. We used five replicates per treatment. No foaming and mixing incompatibility of the spray carrier was observed for all treatments. The adjuvant based on lecithin and propionic acid further acidified the spray carrier and presented the same surface tension as mineral oil. The soybean plants that did not receive chemical treatment had a higher occurrence of diseases, which reduced the productive potential. The addition of adjuvants to the spray carrier did not increase the performance of fungicides in controlling diseases and did not affect the yield components.