Question
I am a president of a condo association and one of my unit owners had concerns about a such a tree near her sidewalk area. I took a sample of her leaves and hers have like a dark mold on the tops of the leaves and her sidewalk also is blackened below.  I took another sample at another site and the leaves from that tree were bright green and had no symptoms as hers did.  What could cause this problem? We have landscapers that treat our complex's lawn, bushes, and shrubbery.  Do I need to tell them specifically to treat this particular tree with Sevin?  The tree is approxiamately 19-20 years old.  I see no other problems with the tree other than the black mold,  no dead leaves or browning.

Answer
It sounds like an insect called  a scale. These insects live under a shell like structure and suck the plant juices from the plant and secrete a substance called Honeydew. Honeydew is high in sugar content and sticky. A sooty mold will grow on the honeydew. This is what you are seeing on the leaves, Control the scales and the sooty mold will go away.
I would treat the tree with an insecticide called Bayer Advanced Tree and Shrub Insect Control--this is applied to the soil around the tree and the roots will absorb the insecticide and transport it to the leaves and twigs and when the insect sucks the plant juices it it killed. Sprays can work but since the scale in under a shell it it hard to get the contact insecticides to the insect. There is a short period in the scales life cycle that it is not under the shell and the spray will work then but the timing of these sprays is difficult. Orthene may work as a spray but Sevin will not. For larger trees the spray is hard to get the solution on all the leaves so the soil application would be best. If you use the Bayer product it will take a couple of weeks to work but will last the entire season. Check with your local nursery for this Bayer product. Here is a web link to this Bayer product for more information.

http://www.bayeradvanced.com/product/Tree-Shrub-Insect-Control/concentrate.html