Blackfly and greenfly (aphids) are very common sap sucking pests affecting nearly all types of plants. Colonies are visible around new buds or shoots in spring onwards. Leaves may twist or yellow and become puckered and distorted as they develop.
Some plant viruses, especially of Strawberry and raspberries, cucumbers can be spread via mouth parts of aphids as they move from plant to plant.
Product solution: Use Provado Ultimate Bug Killer Concentrate 2, Provado Ultimate fruit and Vegetable Bug KIller - ready to use / concentrate, Sprayday Greenfly Killer.
Cultural control: Encourage birds into the garden to feed on the aphids ie Blue Tits.