Large willow bark aphid

The large willow bark aphid a very large aphid and can form dense colonies form on the bark of willow trees. It is part of the biodiversity that healthy willow trees can support.   

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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 Britain. It is greyish black and has a characteristic sharks fin shaped tubercle on its abdomen, the function of this structure remains unknown.

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 is often fed upon by wasps and flies. A black sooty mould may develop on the honeydew and, although harmless to plants, can spoil their appearance.

These aphids are part of the biodiversity healthy willow trees can support and are the basis for many food chains. Even high densities of aphids they seem to have no significant effect on the tree's health or vigour.

Control

This aphid is part of the biodiversity that healthy willows can support in gardens and does not unusually need 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 supports many aphid predators.  
If it is decided to attempt control, for example where honeydew is providing a food source for wasps where people are likely to get stung, check willows frequently from spring onwards so action can be taken before a large population has developed.
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 they form an important part of many food chains and can be part of a healthy garden ecosystem
  • Use finger and thumb to squash aphid colonies where practical
  • 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

The RHS believes that avoiding pests, diseases and weeds by good practice in cultivation methods, cultivar selection, garden hygiene and encouraging or introducing natural enemies, should be the first line of control. If chemical controls are used, they should be used only in a minimal and highly targeted manner.
This aphid does not usually need to be controlled. Little can be done to deal with aphids on tall trees as treatment is only likely to be successful if the entire plant is sprayed

  • 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. 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)
  • A systemic containing the active ingredient Flupyradifurone (Provanto Smart Bug Killer) is available for use on ornamentals and selected edibles
  • 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)

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.

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