 
This is a fungal disease called tar spot which is quite common, especially on sycamore. It does not seem to harm the trees. It is not really worth spraying, just rake up as many leaves as you can and dispose of them.
| 
 Gardening Expert:  | 
If you can't find what you are looking for on the website then you can ask one of our experts. To get in touch with us Click Here
We will try to get back to you with an answer as soon as we can.
Did you find this answer useful? Subscribe to our newsletter for gardeing news, projects, special offers and competitions.
Lalbagh Botanical Garden
Bangalore, India
Singapore Botanic Gardens
Singapore
Nongnooch Tropical Garden
Pattaya, Thailand
Pukekura Park 
New Plymouth, New Zealand
Monet's Garden, Giverny
Giverny, France
Powerscourt Gardens
Enniskerry, Co. Wicklow, Ireland