Question
Hello,
I have a young cherry tree (3 years by now)in the garden that each spring from May onwards gets attacked by black ants and weeks later these ants seem to milk blackflies that are populating the young leaves and destroying them. Now in order to get rid of the blackflies I got to get rid of the ants, but try I may, each spring they are back and nothing seems to help. Any ideas? Many thanks

Answer
These black flies are black aphids.  This problem is reported wherever cherry trees are grown. Black Cherry Aphids are the only type of aphids that affect cherry trees. The aphids are small soft-bodied insects about 3mm in length and may or may not have wings. Affected leaves become stunted, twisted and curled. The Honeydew secreted by the aphids drips on the leaves, fruits and surrounding ground. Ants may be present. A black fungus begins to grow on the honeydew where it has fallen. Treatment includes spraying with an insecticide to kill the aphids.
Control the aphids and you will control the ants. Check with your local nursery/ garden type store for an insecticide for black cherry aphids. You can also wrap the lower trunk of the tree with paper and apply tanglefoot to the paper--this sticky tanglefoot will catch the ants and not let them climb the tree. tanglefoot can be found at the garden store also.