Large willow bark aphid

The large willow bark aphid a very large aphid and can cause alarm when dense colonies form on the bark of willow trees. It causes little damage to the trees.

Large willow aphid ( Tuberolachnus salignus ) on Willow ( Salix caprea )

Large willow aphid (Tuberolachnus salignus) on Willow (Salix caprea)

Quick facts

Common name Large willow bark aphid
Latin name Tuberolachnus salignus
Plants affected Willows (Salix)
Main symptoms Large grey aphids in dense colonies on stems
Caused by Sap-sucking aphids
Timing Summer to late winter

What is large willow bark aphid?

Aphids, also known as greenfly and blackfly, are sap-sucking insects. At 5mm in length the large willow bark aphid is one of the largest aphids in the UK. It is greyish black and has a characteristic sharks fin shaped tubercle on its abdomen.

Symptoms

Large willow bark aphid can form dense colonies on willow bark during the summer months. They suck sap from the bark and excrete a sugary liquid called honeydew. This can make the plant and the ground below sticky which often attracts wasps and flies. A black sooty mould may develop on the honeydew and, although harmless to plants, can spoil their appearance.

Despite their numbers, the aphids seem to have no significant effect on the tree's health or vigour.

Control

Despite the large colonies of large willow bark aphid that can develop they seem to have no significant effect on the tree's health or vigour and the presence of this insect can be tolerated.  

Non-pesticide control

Aphids have many natural enemies, including ladybirds, hoverfly larvae, lacewing larvae and parasitic wasps. Pest control products based on natural compounds or with a physical mode of action are less likely to have serious effect on natural predators.

Pesticide control

If they are a nuisance because of the honeydew production, the aphids can be controlled on small trees by spraying insecticides.

  • During the growing season there are many insecticides that can be used. It is only feasible to control aphids on trees that are small enough to be sprayed thoroughly. Aphid infestations on tall trees have to be tolerated
  • Always read the label and use pesticides safely
  • 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

Downloads

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

Biology

The biology of willow bark aphid is not well known and the purpose of the characteristic sharks fin tubercle is unknown. The aphid spends most of its time on willow and dense colonies can form on willow trees during the summer. Reproduction is parthenogenetic and colonies reach their maximum size in autumn.

Colonies can persist throughout much of the winter but generally disappear in February to reappear again in late spring, it is not known where the aphid goes during this time.


Gardeners' calendar

Advice from the RHS

Find out what to do this month with our gardeners' calendar

Advice from the RHS

Did you find the advice you needed?

RHS members can get exclusive individual advice from the RHS Gardening Advice team.

Join the RHS now

Get involved

The Royal Horticultural Society is the UK’s leading gardening charity. We aim to enrich everyone’s life through plants, and make the UK a greener and more beautiful place.