Abstract
Late blight, caused by Phytophthora infestans , is one of the most important potato diseases globally, resulting in significant production losses. The pathogen is highly variable, adapting to newly developed cultivars and fungicides. In this study, several biocontrol agents and chemicals were evaluated in 2021 and 2022 seasons, for efficacy against blight disease in potato under field conditions. Treatments—applied individually and in combinations—included Bacillus , Trichoderma , Bioneem, Lantana extract, phosphite and mancozeb, and a water sprayed control (no chemical). Disease severity was higher in 2022 than in 2021, with slow progression observed between days 7 and 21, followed by a sharp increase from day 21 to day 28. Across the seasons, mancozeb consistently showed the lowest late and early blight infection rates (66.7–75.0%) by day 28, compared to 91–100% for other treatments. However, no significant differences ( p > 0.05) in the area under disease progress curve (AUDPC) were observed among treatments due to the surge in disease severity during the final week of assessment. Among biocontrol options, Trichoderma , Trichoderma + Bacillus and Bioneem were the most effective in suppressing disease. Lantana extract also showed potential but requires further optimisation regarding dosage and application frequency. Whilst chemical control using mancozeb and phosphite remained superior, the combination of Trichoderma + Bacillus is recommended as a promising biocontrol alternative for managing blight diseases in potato production.