It oozes bacteria-laden liquid particularly when the disease reaches the tip of the leaf. Ad Find Florist Online. Here S How To Treat Black Spots On Your Phalaenopsis Orchid Leaves In 2020 Orchid Leaves Black Spot On Roses Orchids If not controlled soon Black Rot will travel form the leaf down toward the crown killing the pseudobulb rhizome and roots. Black spots on orchids . Black Rot is caused by fungi Pythium ultimum and Phytophthora cactorum often has a watery appearance and can quickly kill a plant if not treated before it reaches the rhizome or roots. Small water-soaked spots on leaves surrounded by yellow halos. Initially dirty green in color the infected spot enlarges coalesces and eventually becomes brown or black dried up and sunken. Where these spots occur. Black Rot a fungal disease characterized by soft rotted areas that begin on leaves or new growth then spread to rhizomes and roots. However leaf spotting can also signify a bacterial or fungal disease. ...