To better understand Black Leaf Streak Disease epidemiology, caused by the airborne ascomycete fungus Pseudocercospora fijiensis, we (i) characterized and quantified the inocula, and (ii) highlighted leaf infection. Spore traps and sporeproof bags were placed in Guadeloupe for a year in two banana varieties, one susceptible and one partially resistant to the disease. We combined microscopy, qPCR and image analysis to quantify spore concentrations and lesions. We found conidia in 2.78% (control) and 4.17% (Williams) samples. Using qPCR method, a standard curve was established with a determination coefficient of 0.992. No ascospore was found. The low spore concentrations were discussed in relation with resistance host and environmental conditions.