A mass on my plum tree branches

(Question)

Hello. I have noticed that there are masses growing on the branches of my plum tree. Last year someone told me that it might be harmful. I cut all the branches with the masses. This year they all grew back and it seems like the tree has more masses then before. It looks like almost every brunch has more then 1 mass. I would like to know what it is and if this is actually harmful to my plum tree. I have 2 more trees very close to plum and would’t like them to be infected.
Also my plum tree has not been giving me any crop for last 2 years. I wonder if it has any connection to the masses. Your answer is very appreciated. Thank you. The picture is attached. I can provide more pictures if needed.black mass

(Answer)

Thank you for contacting Toronto Master Gardeners regarding the problem with your plum tree. Plum trees are susceptible to two fungi, black knot and brown rot which are described in three previous answers in our Ask a Master Gardener archive which is reached by this link:

 

Fungal disease in plum tree

We wish you good luck with your plum tree.