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.
Young tender growth is vulnerable to aphid attack. These tiny insects (1mm-7mm long) are usually green or black and breed fast, smothering the plant. In severe cases, growth becomes distorted, leaves curl up, the plant weakens and can die.
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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.
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.