Cypress aphid

Cypress aphid is one of the causes of dieback on conifer hedges. It has become an increasingly problematic on some conifers since the 1980s, particularly on Leyland cypress.

Cypress aphid damage

Quick facts

Common name Cypress aphid
Scientific name Cinara cupressivora
Plants affected Cupressus macrocarpa, Lawson's cypress (Chamaecyparis lawsoniana), Leyland cypress (× Cuprocyparis leylandii) and Thuja
Main symptoms Conifers suffer extensive drying up and browning of the foliage in late summer
Most active April-June

What is cypress aphid?

Cypress aphid is a blackish brown sap-sucking insect that infests the stems of some hedging conifers (Cupressus species especially C. macrocarpa, Thuja occidentalis, Chamaecyparis lawsoniana and x Cuprocyparis leylandii) in early summer. This often causes a gradual drying up and browning of the foliage.

There are a number of aphids found on other conifers and aphid like adelgids can also affect these plants.

Symptoms

  • Yellowing shoots in summer; by late summer many of these will be brown and dead
  • On clipped hedges the dieback can be quite pronounced, with the lower parts often more severely affected than the top
  • A black powdery coating of sooty mould may develop on the stems and foliage, this is often the only symptom which will confirm aphids as the cause
  • Damaged hedges can recover but it is likely to be a slow process

Control

Susceptible conifers that cared for and pruned during the growing season will be more resistant to cypress aphid damage.

Check susceptible plants frequently 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
  • Use finger and thumb to squash aphid colonies where practical
  • Encourage ‘aphid predators’ in the garden, such as ladybirdsground 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

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.

It is difficult to penetrate dense conifer hedges with sufficient thoroughness to prevent conifer aphids causing damage. Where spraying is feasible below are some suitable products for the home gardener;

  • 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

Damage is caused by greyish brown aphids that are active from May to November, reaching peak numbers in early to mid-summer.

  • They suck sap from the stems and even quite light infestations can have a significant effect
  • Although the aphids are 2-4mm long (about 1/8in), they are difficult to see as their colour matches that of the bark 
  • A useful confirmation of aphid damage is the presence of a black sooty mould on the stems and/or foliage, as there are other causes of dieback on conifers
  • Other causes of dieback include poor establishment, weather damage such as drought, scorching caused by wind or extreme temperatures, excessive clipping of a hedge, and root diseases such as honey fungus and Phytophthora root rot


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