The efficacy of biofungicides on cashew wilt disease caused by Fusarium oxysporum

Cashew wilt, caused by the soil borne fungus Fusarium oxysporum, is a fast spreading disease that is currently threatening the cashew industry in Tanzania, which is a major source of income for cashew growers and the country. The disease causes the death of the trees within a few weeks of infection. Cashew seedlings treated with either Bacillus strains or T. asperellum biofungicides developed significantly (p < 0.05) lower disease severity levels (0–7.54%) compared to untreated cashew seedlings (0–27.27%). No disease symptoms were observed on cashew seedlings treated with Bacillus velezensis strain 13/A + 3 at 0.5, 1.0, and 2.0 mls of a spore suspension at 1 × 104, 2 × 104 and 3 × 104 ml of spore suspension. Under field conditions, cashew trees treated with biofungicides developed significantly (p < 0.001) lower disease severity of 0–11.49% and 0–12.98% in both seasons (2019/2020 and 2020/2021 respectively) compared to the untreated controls (60.05% and 59.71% respectively). Results from this study indicate the potential of the tested biological control agents in the management of cashew wilt disease caused by F. oxysporum. However, further studies are recommended to determine the shelf life and effectiveness of the biological control agents particularly in a field setting, as well as the efficacy of various formulations.