"P. cactorum" is also one of the causal agents of black rot of orchids. When infecting orchids, this organism first produces small black lesions on the pseudobulbs of the orchid, which then enlarge and may engulf the entire pseudobulb, leaf, or move through the rhizomes to other portions of the plant prior to killing it. Diagnosis of orchid black rot by "P. cactorum" is through the identification of lemon shaped zoosporangia with either a or a short pedicel, the presence of oospores, or molecular identification. Since there are multiple species of "Phytophthora" that are capable of causing disease on orchids, classification only to the genus level is required for proper prescription of disease management techniques.