Question
I have a rose of Sharon that is about 8' tall and has a trunk of about 5-6" diameter so it looks like a small tree. I have noticed that all over many of the branches greenish spots the size of quarters or bigger general areas on the branches. The trunk looks different in the green growth commonly seen on most trees. What might it be? And how do I treat it. Is this an indication that the rose of Sharon is dying?

Answer
Randy:

If further clarification is requested on the identification of these spots, please send along a photo.  Try to get as close as you can to take the shot.  Take several and send the best one. Be sure to review them before sending to be sure they are in focus.

From your written description, these circular spots sound like lichens.  These are often greenish/gray and look like patches.  They are not considered disease organisms.  You may wish to look at photos of different lichens on the internet to compare to your spots.  These organisms are often seen on older or declining plants.  Common in the shady areas. They can also grow on rocks, fence posts and even power lines.

Another possibility is an algae.  Also seen in moist/shady areas. Mostly superficial, however a very few can cause a stress on plants. Chemicals for control are rarely prescribed since negative effects are negligible. Selective pruning to allow light penetration and reducing relative humidity can be of some help, but probably more trouble than it's worth.

Regards
Steve