BACKGROUND: Black sigatoka is the main disease of banana crop production and is controlled by using either systemic or contact fungicides through spray applications. Biological efficacy is typically assessed on a whole cropping cycle with a natural infestation and periodic spray applications. Developing a faster methodology for assessment of the biological efficacy of a contact fungicide offers promising perspectives for testing current and new fungicides or application techniques. RESULTS: The methodology is based on the time of occurrence of the first BLSD symptoms. An artificial infestation protocol was optimized by multiplying the infestation spots and by covering the infested plants. Biological efficacy tests were based on a single spray application after infestation combining three mancozeb dose reductions and two nozzle types. Results demonstrated that a 50% reduction in the mancozeb rated dosage gave significant efficacy independently of the nozzle type, with a reduction of the number of lesions of up to 55% compared with control plants. CONCLUSIONS: The described method provides rapid and significant infestation. Further comparison of spray settings and fungicide doses was possible. This methodology will be tested at the plantation scale over a longer period covering the whole crop cycle.