I recently took a walk in Umstead Park and noticed this tree. What’s that black thing up there?
As I got closer to the tree, I noticed that there was more black stuff on the other side.
Once I was next to the tree, I could see that there was some liquid oozing from the large growth at the top of the tree.
After doing some investigating at home, I think this is Black Knot fungus, Apiosporina morbosa. This fungus infects plum and cherry trees. The fungal spores are released during the wet spring and infect new growth. As the fungus grows, it causes abnormal growth in the tree, called a gall. The gall is green at first, but as it matures it becomes black and hard. The black gall releases the spores to spread the disease. The liquid is the tree reacting to the infection.
You can read more about Black Knot at the University of Minnesota Extension.
Have you seen a tree infected with Black Knot fungus?