Wart-Like Growths on Gardenia Trees
Our beautiful Gardenia tree is struggling. It has developed some ugly large black "bunion" type growths on the joints of the larger branches. They are very hard and lumpy, range from 2-3 inches in diameter, and seem to have developed from the inside out. The bottom branches aren't blooming at all and the leaves are sparse and yellowing. The top of the tree is still trying to bloom and looks a bit healthier, but I am worried that the "infection" will ultimately take over the tree and kill it. What is this and what can be done?
This appears to be a canker and gall disease on your Gardenia.
These links have information and treatment methods.