Do not spray chemical insecticides in the garden. Do not spray soap onto an insect if you think it may be beneficial. Read on for more information about beneficial insects. Control honeydew-feeding ants, which help protect aphid colonies. Set up a small dish in an ant path, or at the bottom of the affected plant.
Ants take the mix back to their colony, which is then destroyed.
This works particularly well for large trees infected with aphids. In large trees, sometimes aphid population occur year after year unnoticed, except for the sticky mess that gets on cars and deckchairs sitting underneath. The borax method pointed out above may help, but a lime-sulphur spray in the winter would likely be best. Lime sulphur can only be sprayed on plants when they are dormant and leafless. Ask for Dormant Oil Spray at your local nursery, but don't expect them to have any until fall.