Aphids: How to Recognise Damage?
You can recognise aphid damage by the many white cast off skins left on the leaves or growth points of the plant. Aphids suck the nutrients and sap out of green plants. Every time an aphid bites into the plant, it forces its saliva into the plant cells. This infects the plant with viruses and weakens it. As a result leaves will discolour, wilt or become sticky.
Aphids are usually green, but can also be white, black, yellow, red or purple. Usually they are no bigger than half a millimetre. They look for the growth points of a plant, such as the top of a young stem.