What are aphids?
Aphids are small insects in the Aphidoidea family. Many different aphid species affect fruit trees, such as blackfly, greenfly, green peach aphid and woolly aphids. They feed on sap by injecting their stylus into the phloem channels of the leaves. The sap is under pressure and so it is passively forced into the aphid’s alimentary canal. Many aphid species are specific to just one plant species, while others are capable of living on many different types of plants. Eggs hatch in spring giving rise to females which can then reproduce without fertilization and producing live young, a system that enables rapid increase in the aphid population on a fruit tree. In autumn, aphids reproduce sexually and lay eggs that overwinter.
Often the most obvious sign of aphid infection is the presence of ants. Aphids are farmed by ants, which protect them on the plants in return from the honeydew excreted by the aphids. Some ant species actually store aphid eggs in their nests over the winter, and carry the newly hatched aphids back to the leaves in the spring.
How do aphids damage fruit trees?
Aphids reduce the plant’s vigour and cropping potential by consuming sap with its nutrients. They distort the growth of leaves, and can infect the plant with viruses. The honeydew that the aphids exude makes the leaves sticky and causes the growth of sooty moulds, which reduce photosynthesis. Aphid damage can be seen primarily by the curling of young leaves, and often by the activity of ants farming the aphids. You will find the insects clustered underneath the leaves and on the leaf stems.
How to get rid of aphids on fruit trees
Fruit tree aphid control: aphids are eaten by many birds and insects. Ladybird larvae can be up to 12 mm long, and are grey-black with orange, red or white markings. Hoverfly larvae are maggots with flat, whitish or green, semi-transparent bodies up to 12 mm long. The larvae feed on aphids, and later, adult hoverflies are important pollinators. Lacewing larvae are up to 8 mm long and feed on aphids. Predatory midge larvae are yellow-orange maggots about 3 mm long that feed on aphids. Earwigs are useful in controlling aphids on fruit trees. So it is good to encourage the presence of insects such as ladybirds, hoverflies and lacewings, for example by providing insect hotels in your garden. Some small birds eat aphids, such as sparrows, and these can be encouraged by installing nest boxes in your garden or orchard. Watch a video on insect hotels.
However in some seasons, there may be too many aphids to be controlled by natural predators. In this case, how to kill aphids on fruit trees? Systemic insecticides can be used, typically from late April, but these have a harmful effect on the beneficial insects in the garden, and in any case, effective insecticides are no longer available to gardeners. Spraying aphids with soapy water is a good organic method of controlling them. Just mix a litre of water with a few drops of washing-up liquid. This treatment should be performed every 2 or 3 days for a couple of weeks. At garden centres, you can purchase non-toxic fatty acid sprays or horticultural soap mixture, which work on the same principle. Sometimes it may be necessary to cut off shoots heavily infested with aphids and destroy them. Watch a video on how to control aphids on apples.
Some aphids, such as woolly aphids, are more diffcult to control. A good method is to use luke-warm water with some detergent, directly brushing the affected locations.
It is a good idea to spray the trees with a winter wash during dormancy in winter. This helps control the overwintering eggs.