Cypress aphid

Cypress aphid is one of the causes of dieback on conifer hedges. It has become an increasingly problematic on conifer hedges 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 Conifer hedges 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 of the foliage.

There are a number of  aphid pests of 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
  • Damaged hedges can recover but it is likely to be a slow process

Control

Non-chemical control

A hedge that is cared for and pruned during the growing season will be more resistant to cypress aphid damage

Chemical control

  • It is often difficult or impractical to spray large dense hedges thoroughly, and in years when the aphid is abundant, some damage will occur
  • Tall or dense hedges can be impossible to treat
  • Spray in early summer to prevent damage occurring
  • Systemic products such as the neonicotinoid acetamiprid (e.g. Bug Clear Ultra) are most likely to give good control. Contact insecticides such as deltamethrin (e.g. Bayer Provado Ultimate Fruit & Vegetable Bug Killer), lambda-cyhalothrin (e.g. Westland Resolva Bug Killer) and cypermethrin (e.g. Py Bug Killer Concentrate) or organic sprays, such as pyrethrum (e.g. Defenders Bug Killer) may give some control.
  • Do not spray near plants in flower due to 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

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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