Q&A Diseases: Cherry tree

I have a mature Prunus serrula cherry tree that has an abundance of the most amazing, large, solidified lumps (of sap, we presume) all over the bark, which feel like plastic. What are they, why have they formed, is it a problem and what should I do?

Brad: This condition is often referred to as gumosis where a resin-like sap oozes from the bark and then hardens like pieces of clear varnish. It is linked to the plant's immune system and may indicate an infection like bacterial canker, or just the plant trying to 'plug' gaps where the bark has been damaged.

Check your tree to see if there are any other symptoms, such as lots of small holes in the leaves, which could be another indicator of bacterial canker. If your tree is healthy and growing vigorously, it may be able to fight off infections without help.