My basswood has been dropping leaves this summer. If you look at the underside of the tree, the bottom side leaves have black spots. I had a tree removal guy tell me over the phone it was fungus and he has seen several cases this year. the picture below should clearly show the black dots. Is this indeed fungus? If so, what is the disease called? what steps should be taken to save the tree? Your assistance in this matter is greatly appreciated.
This looks like linden leaf blotch. Yes, it is a fungus. These kinds of diseases do not usually pose a threat to the tree's health, unless a significant portion of the canopy is destroyed for two or three years in a row. We had a great deal of rain this year, so leaf spot diseases are popping up all over. I don't recommend any treatment except careful cleanup in the fall. Here is a reference:
Thank you so much Dennis W. your advise/direction is GREATLY appreciated.