| Added on 02/01/2012 | Pest/Disease |
Cypress Aphid
Cinara cupressi or Cinara cupressivora
This common pest is causing increasingly widespread dieback of several popular hedging conifers in the UK. It affects Cupressus species (including Monterey & Italian Cypresses), probably all cultivars of x Cupressocyparis leylandii (Leyland Cypress) and Chamaecyparis lawsoniana (Lawson Cypress, and occasionally Thuja occidentalis (Eastern White Cedar).
|
Aphids cause damage by sucking cell sap from within plant tissues. The Cypress Aphid causes patches of yellow foliage from the base of the tree in late spring and summer, which later turns brown and dies. Further branch die-back spreads upwards and to adjacent plants.
The aphids are active from May to November, with numbers peaking in early to mid-summer. Although they are comparatively large aphids (2-4mm long) with pear-shaped grey to yellow-brown bodies, they can be difficult to see.
Along with the direct foliage damage, sooty moulds grow on the honeydew which is excreted by the aphids during feeding, and which lands on adjacent branches and foliage. This is a useful confirmation of aphid damage, and may help to exclude other causes of conifer dieback with superficially-similar symptoms, which include drought, wind/heat scorching, chemical and de-icing salt damage, Coryneum Canker, and root diseases such as Honey Fungus and Phytophthora.
|
An infestation on a specimen tree causes crown thinning and loss of lower branches. On clipped hedges the dieback can be pronounced and any screening effect lost, although often lower parts of the plants are more severely affected than the top. The growth habit of these species means that there is likely to be very little regrowth on damaged tissues, and so the visual impact is long lasting.
Originally arriving from southern Europe in the late nineteenth century, the aphid is more common and widespread in the UK in some years than in others, but is most frequent in the south and east of England. Leyland Cypresses were first reported as being infested in the 1980s, with 1988 & 1989 being especially bad years. The frequency of these 'bad years' seems set to increase as our winters become milder - allowing adults to over winter more successfully on plants.
|
Smaller plants can be treated with an approved aphid control insecticide as soon as symptoms are seen (usually early summer). Domestic products now available contain either imidacloprid (Bayer Provado Ultimate Bug Killer Concentrate) or bifenthrin (Scotts Bug Clear, Doff All-In-One Garden Pest Killer or Bayer Sprayday Greenfly Killer Plus).
It is not cost effective to treat large hedges, or for an arborist to undertake treatment with professional pesticides, as it is unlikely that either will halt further dieback, or prevent repeat damage later in the year. Badly damaged hedges may recover slowly, but are probably best removed and replanted with immune species.
References:
BUCZACKI, S. & HARRIS, K. (1981), Pests, Diseases & Disorders of Garden Plants, Harper Collins, London,
STROUTS, R.G. & WINTER, T.G. (1994), Diagnosis if ill-health in Trees, HMSO, London, (2nd edn.),
Text and photographs by Ian Monger October 2007 except photo 2 from www.j-alemany.com