Question

tree trunk of Tibouchi  

Tibouchinas   Dear Dr. Stephen Vann
I'm having a Tibouchinas in my Garden. For some reason, there're lots of green patches appear on it's trunk。It looks like mold with black colour in the back of the patch.Do you know what's wrong with it and how I can cure it.
Many thanks in advance!

Best Regards,
Rin

Answer
Hi Rin:
Thanks for your question and images.  From your two photos, these "greenish patches" appear as merely lichens.  These organisms are not considered disease agents.  You can read about them from the web address below or "Google" them on the internet.

http://www.uaex.edu/Other_Areas/publications/PDF/FSA-7554.pdf

Lichens tend to occur on older woody plants that may be stressed for some other reason.  We also tend to see these things on plants that are in the shade sometimes too.

Regards
Steve