Monilinia vaccinii-corymbosi is the cause of mummy berry disease of commercial blueberries (Vaccinium spp.) grown in the United States and Canada (1). Ovaries of blueberry flowers are infected by the conidia (asexual spores) of this pathogen. However, despite their importance in disease initiation, little is known of the ultrastructural features of these conidia. The only ultrastructural data on these spores has come from the work of Batra (2) who used scanning electron microscopy to describe the morphology of the so-called “disjunctors” which connect adjacent conidia of M. vaccinii-corymbosi. The presence or absence of disjunctors is an important taxonomic character in the genus Monilinia (1) but little is known of their development and exact nature. The objective of this study was, therefore, to elucidate details of conidium and disjunctor development in M. vaccinii-corymbosi.