Today 
There are many species of aphid, often with its own favourite host plants and particular life cycle. Greenfly and blackfly are the most familiar, but there are also yellow, red, orange and brown aphids. Aphids usually spend the summer on one plant, moving to a host plant to overwinter. They breed at an alarming rate - females can give birth to live young when only a week old. They are sap-sucking pests and the excess sap is excreted as honeydew. This sticky residue falls on to the lower leaves of the plant, attracting black sooty mould, which inhibits photosynthesis and deprives the plant of energy.
Solution
Organic
Natural predators, such as birds, earwigs, ladybirds, lacewings, hoverflies, ground beetles, spiders and parasitic wasps are a gardener's best allies. Some of these are available as biological controls, however, they need time to tackle the problem, so don't expect them to hoover up the aphids overnight.
Small clusters of aphids can be squished with your fingers or washed off with a strong jet of water.
Insecticidal soap sprays are effective, but must come into contact with the pest to work.
Chemical
Avoid feeding plants with nitrogen-rich fertiliser, as it encourages soft, sappy growth that's especially vulnerable to aphid attack. There are many products available to control aphids - if you intend to use them on edible crops, make sure you follow the instructions carefully. Bifenthrin is used in contact insecticides, which are sprayed directly on to the pest. Imidacloprid and thiacloprid are found in systemic products, which are absorbed by the plants, before being taken up by the aphids.
