In order to know the origin of the resistance in order to develop a control strategy that respects the environment and human health, this study was initiated. More specifically, it should make it possible to determine the reaction of wild strains of Mycosphaerella fijiensis to systemic synthetic fungicides in areas of intensive cultivation of dessert bananas for export in Côte d'Ivoire. Samples of leaves from dessert and plantain banana trees affected by Black Leaf Streak Disease at stages 3 and 4 were taken at a distance of at least 10 km from the industrial plantations and then transported to the laboratory for fungicide sensitivity tests on agar medium according to the method proposed by Van Den Berg Loridat in 1989 and modified by Kobenan and al in 2008. These tests revealed remarkable efficacy of all fungicides on all wild conidia of Mycosphaerella fijiensis regardless of their origin. For the triazoles the inhibition rates ranged from 67.45% to 75% for tebuconazole, 67.34% to 79.41% for epoxyconazole, and 70% to 80.14% for tebuconazole. As for methyl thiophanate, germination rates were between 0 and 11%. For azoxystrobin, germination rates were between 0 and 20 %. However, the same tests carried out in industrial plantations revealed losses in the effectiveness of certain fungicides of the triazole family in certain areas. This loss of efficacy observed in plantations regularly treated with fungicides is due to the repeated use of these fungicides without any real alternation (of the different families of active ingredients), which would have eliminated strains sensitive to these active ingredients and facilitated the proliferation of non-sensitive strains.