Data about new for Ukraine lichenicolous fungus Phoma cladoniicola Diederich, Kocourk. & Etayo are reported. It was found on sand dunes in the Lower Dnieper (Kherson region, Ukraine). The fungus causes the disease with mosaic dying off of lichen thallus in Cladonia phomosis . one of dominant species of the biological crust in the sand-dunes ecosystems of Lower Dnieper. The lichenicolous fungus is found on C. arbuscula, C. subrangiformi and C. subulata for the first time.