Woolly beech aphid

In some years, woolly beech aphid can be abundant and whilst its appearance can be alarming it rarely causes damage to trees and hedges.

Woolly beech aphid

Quick facts

Common name Woolly beech aphid
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
Timing April-August

What is beech woolly aphid?

Aphids, also known as greenfly and blackfly, are sap-sucking insects. 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 usually be tolerated. 

Symptoms

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

Control

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.

Non-pesticide control

  • Where possible tolerate populations of aphids, woolly beech aphid is unlikely to have any affect on the health of the trees
  • 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

Pesticide control

Control with pesticides is usually unnecessary and only feasible on beech trees and hedges that are small enough to be sprayed thoroughly

  • Organic sprays, such as natural pyrethrum (e.g. Bug Clear Gun for Fruit & Veg, Neudorff Bug Free Bug and Larvae Killer), fatty acids (e.g. Solabiol Bug Free, Doff Greenfly & Blackfly Killer) or plant oils (e.g. Vitax Plant Guard Pest & Disease Control, Bug Clear for Fruit and Veg) can give good control of aphids. These pesticides have a very short persistence and so may require reapplication to keep aphid numbers in check. Plant oil and fatty acid products are less likely to affect larger insects such as ladybird adults
  • Plant invigorators combine nutrients to stimulate plant growth with surfactants or fatty acids that have a physical mode of action against aphids (e.g. Ecofective Bug Control, RHS Bug and Mildew Control, SB Plant Invigorator and Westland Resolva Natural Power Bug & Mildew). These products contain some synthetic ingredients and so are not considered organic.
  • More persistent contact-action insecticides include the synthetic pyrethroids lambda-cyhalothrin (e.g. Westland Resolva Bug Killer), deltamethrin (e.g. Provanto Ultimate Fruit & Vegetable Bug Killer, Provanto Sprayday Greenfly Killer) and cypermethrin (e.g. Py Bug Killer)
  • The systemic neonicotinoid insecticide acetamiprid (e.g. Bug Clear Ultra) is also available

Follow label instructions when using pesticides
Plants in flower should not be sprayed due to the danger to bees and other pollinating insects
Inclusion of a pesticide product does not indicate a recommendation or endorsement by RHS Gardening Advice. It is a list of products currently available to the home gardener

Download

Pesticides for gardeners (pdf document)

Biology

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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