<p>This study aimed to determine the optimal and cost-effective strategy for controlling powdery mildew disease (PMD) in cashew plants by incorporating resistant varieties, cultural practices, and chemical control into a mathematical model. A deterministic model was developed and analyzed to study the impact of implementing these three time-dependent controls on disease transmission dynamics. Pontryagin’s maximum principle was employed to derive necessary conditions for the existence of optimal controls and to determine the most effective disease management strategy. Additionally, cost-effectiveness analysis was conducted using the incremental cost-effectiveness ratio (ICER) to compare the efficiency of various strategies. The results suggest that the strategy involving the use of resistant cashew varieties in combination with cultural control methods is the most cost-effective and achieves greater health impact at a lower cost. Therefore, farmers are advised to prioritize preventive measures such as planting improved, disease-resistant cashew varieties, timely pruning, and proper sanitation to ensure optimal and cost-effective control of PMD. This study provides a scientific basis for guiding farmers toward integrated and sustainable disease management practices.</p>