Question
My Hackberry has "warts" on the leaves and the leaves are turnig yellow and falling. The warts are round, raised nasty little things. What to do....my landscaper says they are harmless

Answer
These are caused by tiny insect and the landscaper is correct they will not effect the overall health of the tree just make it look bad or could cause it to drop leaves sooner in the fall. Here is a web link to some of these insects. I would not worry about these.

http://www.extension.umn.edu/distribution/horticulture/DG1009.html