I have a very old, large maple tree in my garden. The plants and garden furniture under which is covered with black sticky mold. I understand this is from green fly, but as spraying with soapy water (the tree) isn't really practical, is there any other non-chemical way of dealing with them?
Certified GKH Gardening Expert
You can try spraying what you can reach with neem oil. It is an organic, people safe oil and the nice thing about it is that the tree will absorb it and carry it up to the parts of the tree you can't reach and kill the pests there.
For a truly non-chemical solution, you can try predators such as Aphidolytes or Aphidius. These are midges that prey on green fly and will kill them. They should be available from reputable plant nurseries.