Santa Rosa Plum – Black Crusty Fungus

Q: Six years ago I planted a Santa Rosa plum and it has flourished. This big, beautiful specimen has a black crusty fungus on most of the stems. What is this? Can I save my tree? 

A: Your plum tree has black knot fungus. At this point, there is nothing you can do about it except to prune out the affected limbs. This may remove most of the tree and it likely wont produce plums in the future. The fungus spreads by wind and infected pruning tools. It does not live in the soil. It only affects plants in the Prunus family: plums and fruiting or ornamental cherries. Apples, figs or pears would all be appropriate to plant after you remove the plum.