The foliage becomes sticky with honeydew ultimately developing into sooty moulds.
In heavy attacks the foliage at the shoot tips becomes distorted and leaves dry up.
The eggs laid the previous autumn hatch in April and infestations can develop by late May to June.
By midsummer the infestations decline as the winged aphids fly away leaving small, non-feeding nymphs in their wake.
These complete their development in autumn when the females lay their eggs on twigs.
Control with a suitable insecticide when the aphid is first seen, and before they fly off.
Where large inaccessible trees are involved treatment will be virtually impossible, this means the aphid will just have to be tolerated.