Phomopsis Canker (Phomopsis spp.) - Phomopsis is a fungal pathogen that infects an oak tree by way of an open wound on the tree. Phomopsis can also infect trees via buds and progress further down the stem. Wet, humid, and shady conditions help foster this fungus. Phomopsis causes woody growths or cankers on the tree which once established, disperse spores from various cream-colored fruiting bodies.