Integrating a Bacillus-based product with fungicides by foliar application to protect soybean: a sustainable approach to avoid exclusive use of chemicals.

BACKGROUND: Biological control is widely applied against soybean (Glycine max L.) soil-borne pathogens by furrow or seed treatments. The efficiency of bioproducts and timing of application by foliar sprays against soybean pathogens needs to be more fully understood. This work investigated the efficiency of foliar application with a Bacillus subtilis-based product (BBP) to protect soybean from multiple pathogens and the best moment to apply it considering its compatibility with fungicides. RESULTS: Foliar applications (from stages V6 to R4) with BBP, mancozeb (M) and systemic fungicides (S) applied against Asian rust (Phakopsora pachyrhizi), BBP followed by S (BBP-S), BBP along with S (S + BBP), S along with M (S + M) or water were carried out in a soybean field for two years. The treatments S + BBP, S + M and BBP-S reduced the severity of Asian rust by 82% compared to the control. Except for M, all treatments reduced the severity of other foliar diseases by >60%. The defoliation was reduced by BBP and BBP-S, whereas the yield was 25% higher than control by using BBP, S + M, S + BBP or BBP-S. Also, the incidence of Fusarium sp. was significantly reduced on seeds from treatments BBP and BBP-S. The compatibility tests in Petri dishes demonstrated that all fungicides decreased the bacterial growth when applied along with BBP, whereas previous applications of BBP did not reduce the bacterial growth. CONCLUSIONS: The BBP protected soybean against multiple pathogens, reduced defoliation and promoted soybean yield similarly to conventional fungicides, but in general, the early application of the BBP was the most efficient protection. © 2022 Society of Chemical Industry.