Question
It is autumn in South Africa %26 my beautiful oak tree's leaves are infected with a black fungal (?)disease. In fact, the wall %26 paving around the tree are also turning black. There is a tacky gum-like substance deposited on my windscreen when I park my car underneath the tree.It is a huge old tree and desperately needs help.Can you please advise?

Answer
Sounds like either aphids or a scale insect--both insects will suck the plant juices from the plant and secrete a substance called honeydew which is high in sugar content and sticky. A sooty mold will grow on this sugar making the black. Control the scales and aphids and the honeydew will go away. Treat the tree with an insecticide called Bayer Advanced Tree and Shrub Insect Control. This is applied to the spoil around the tree and the roots will carry the insecticide to the leaves and stems and when the insects suck the plant juices they are killed. It will take a couple of weeks for the insecticide to get to the top leaves depending on the tree size. Her is a web link to this product check with your local nursery fro this product. http://www.bayeradvanced.com/tree-shrub-care/products/12-month-tree-shrub-insect...