Microcyclus ulei, a fungus causing South American leaf blight of rubber tree, can only be isolated from asexual spores, which remain on a lesion just for a few days. This is a serious problem when wishing to study the diversity of the fungus on wild trees, which bear stromatic lesions almost exclusively on old leaves. The proposed technique can be used to isolate the fungus easily from sexual spores occurring in these stromata, even on leaves that are several months old.