In vitro Evaluation of Commercial Fungicide Othello® (Azoxystrobin and Difenoconazole) Against Cocos nucifera and Elaeis guineensis Foliar Pathogens

Cocos nucifera L. and Elaeis guineensis Jacq. are important cash crops that provide a source of livelihood for millions of farmers in Africa. The seedling stages of these crops are mostly susceptible to diseases of which fungi leaf spots and blight rank high, which negatively impacts the development. As part of efforts to minimize the development of resistance against fungicides, we evaluated the efficacy of the commercial fungicide Othello®, which is composed of two different fungicide groups Azoxystrobin and Difenoconazole against oil palm and coconut foliar pathogens in vitro. The main aim of this study was to assess Othello® against Bipolaris bicolor, Curvularia sp., Colletotrichum sp., and Neopestalotiopsis species. Each pathogen was plated on PDA amended with different doses of the fungicide in a completely randomized design, with five replicates per treatment, and data was analyzed with an R statistical tool. The results from our research revealed that all tested concentrations of Othello® (2.5 µL per mL, 5 µL per mL, and 7.5 µL per mL) caused 100 % mycelial growth inhibition in all four pathogens compared to the control (unamended PDA plates) (P < 0.01) after 28 days of incubation. Our subsequent study showed that even the lowest concentration of Othello® (0.5 µL per mL) caused 100 % mycelial growth inhibition. The lowest dosage effect of the fungicide was more pronounced in Neopestalotiopsis sp. with 100 % inhibition while ≤ 80 % inhibition was recorded for Bipolaris bicolor and Curvularia species. This research lays the foundation for the potential use of Othello® to manage B. bicolor, Curvularia sp., Neopestalotiopsis sp., and Colletotrichum sp., but may require semi- and open-field validation.