Latin name Phyllaphis fagi
Plants affected Beech trees and hedges
Main symptoms Pale yellow aphids covered by white waxy 'fluff' clustered on the underside of the leaves. Foliage sticky with honeydew
Caused by A sap-sucking insect
What is beech woolly aphid?
Woolly beech aphid can make the foliage of beech trees and hedges sticky with the honeydew it excretes but causes no long term harm and can be tolerated.
Aphids are sap-sucking true bugs and are an important part of many food chains, supporting many predators. They range in size from 1 to 7mm (¼in or less) long. Some aphids are known as greenfly or blackfly, but there are species that are yellow, pink, white or mottled. There are more than 500 aphid species in Britain. Some feed on only one or two plant species, but others can be found on a wide range of plant hosts. Almost any plant can be affected, including ornamentals, vegetables, fruits, greenhouse plants and houseplants.
Woolly beech aphid is quite distinctive;
- In late spring, fluffy white patches appear on the underside of beech leaves
- Under this waxy covering are pale yellow aphids that are sucking sap from the foliage and young stems
- The aphids excrete a sugary substance called honeydew that coats the upper leaf surface and makes the foliage sticky
- A black sooty mould may develop on the honeydew
- Woolly beech aphid does not occur on plants other than beech. The appearance of insects covered in white waxy material on other plants will be other species, such as woolly aphid on apples and pyracantha, scale insect egg masses or in glasshouses mealybug
Woolly beech aphid does not usually seriously affect the health of beech trees and hedges and control is usually not required. When large populations do occur this tends to be temporary and plants are not usually affected year after year.
Check beech plants frequently from spring onwards so action can be taken before a damaging population has developed. Little can be done to deal with aphids on tall trees as treatment is only likely to be successful if the entire plant can be reached. When choosing control options you can minimise harm to non-target animals by starting with the methods in the non-pesticide control section. If this is not sufficient to reduce damage to acceptable levels then you may choose to use pesticides. Within this group the shorter persistence pesticides (that are usually certified for organic growing) are likely to be less damaging to non-target wildlife than those with longer persistence and/or systemic action.
- Where possible tolerate populations of aphids, woolly beech aphid is unlikely to have any affect on the health of the trees. Aphids form an important part of many food chains and can be part of a healthy garden ecosystem
- Encourage aphid predators in the garden, such as ladybirds, ground beetles, hoverflies, parasitoid wasps and earwigs. Be aware that in spring aphid populations often build up before natural enemies are active in sufficient numbers and then give good control
Control with pesticides is usually unnecessary
Woolly beech aphid overwinters as eggs that are laid around buds and in bark crevices in autumn. The eggs hatch in spring a few weeks after new foliage has appeared.
The pale yellow aphids suck sap from the underside of leaves and can form dense colonies that are hidden under a white waxy fluff that is secreted by the aphids. They also excrete a sugary honeydew that makes the foliage sticky and encourages the growth of sooty moulds. Heavily affected leaves may be distorted but otherwise the tree’s growth is unaffected.
For most of spring and summer, the aphids are wingless forms that reproduce by producing live young. In mid-summer, winged forms develop that fly off in search of new host plants. These winged woolly beech aphids can be mistaken for glasshouse whitefly or woolly aphid, neither of which occur on beech.
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