Compatibility of a biopesticide based on the yeast Rhodotorula mucilaginosa (Lv316) with chemical fungicides used in blackberry crops

Blackberry (Rubus glaucus Benth.) is affected by several diseases, such as grey mould (Botrytis cinerea Pers.), downy mildew (Peronospora sp.) and anthracnose (Colletotrichum sp.), which are managed by chemical fungicides. The yeast Rhodotorula mucilaginosa Lv316 demonstrated high efficacy against grey mould and was formulated as a new biopesticide with the potential to replace some recommended agrochemicals. However, the use of chemical fungicides for the control of two other main diseases of blackberry, downy mildew and anthracnose, are still required, and it is possible these may negatively affect the biopesticide. The purpose of this study was to assess the compatibility between the biopesticide containing Lv316 (107 cells ml−1) and chemical fungicides commonly used to control downy mildew and anthracnose. In vitro experiments indicated that Lv316 was compatible with carbendazim (≤ 200 ppm), dimethomorph (≤ 400 ppm), mandipropamid (≤ 1125 ppm), and azoxystrobin (≤ 375 ppm), but was negatively affected by difenoconazole (≤ 25 ppm) and copper hydroxide (≤ 1513 ppm). On detached blackberry flowers, difenoconazole and azoxystrobin showed a 63.92% and 58.70% reduction in the incidence of grey mould, respectively, while the biopesticide reduced the incidence by 60.26%. Under field conditions, the biopesticide and the fungicide prochloraz, recommended for B. cinerea control, reduced the incidence of grey mould by 53.49%, similar to the combine application of biopesticide with azoxystrobin (50.61%). These results suggest that the biopesticide based on Lv316 could replace the fungicide prochloraz for controlling grey mould and is compatible with azoxystrobin for an integrated management strategy to control foliar diseases in blackberry crops.