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

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.

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. Where serious infestations do occur this tends to be temporary and plants are not usually affected year after year.

Aphids have many natural enemies, including ladybirds, hoverfly larvae, lacewing larvae and several parasitoid wasps. 

Pesticide control

  • Control with pesticides is usually unnecessary and only feasible on beech trees and hedges that are small enough to be sprayed thoroughly
  • If infestations are very severe affected plants can be sprayed in April-May. It is not worthwhile spraying later in the summer, as by then any damage has already occurred and the infestation will be past its peak and in decline
  • Organic sprays, such as natural pyrethrum (e.g. Bug Clear Gun for Fruit & Veg, Ecofective Bug Killer), fatty acids (e.g. Solabiol Bug Free, Doff Greenfly & Blackfly Killer) or plant oils (e.g. Vitax Organic 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
  • More persistent insecticides include the synthetic pyrethroids lambda-cyhalothrin (e.g. Westland Resolva Pest Killer), deltamethrin (e.g. Provanto Ultimate Fruit & Vegetable Bug Killer) and cypermethrin (e.g. Py Bug Killer)
  • The systemic neonicotinoid insecticide acetamiprid (e.g. Bug Clear Ultra) is also available
  • Plants in flower should not be sprayed due the danger to pollinating insects
  • Inclusion of a pesticide product does not indicate a recommendation or endorsement by the RHS. It is a list of products currently available to the home gardener

Download

Pesticides for gardeners (Adobe Acrobat pdf document outlining pesticides available to gardeners)

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 infested 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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