Juniper scale

Small sap sucking juniper scale insects can encrust junipers (Juniperus species) and some other conifers such as cypresses (Cupressus and Chamaecyparis), Leyland cypress (x Cuprocyparis leylandii) and Thuya

Juniper scale on juniper

Juniper scale on juniper

Quick facts

Common Name Juniper scale
Scientific Name Carulaspis juniperi
Plants Affected Junipers (Juniperus spp.) cypresses (Cupressus and Chamaecyparis), Leyland cypress (x Cuprocyparis leylandii) and Thuya
Main Symptom Small whitish brown scale insects on foliage
Most Active Summer

What is juniper scale?

Juniper scale is one of several species of scale insect encountered by gardeners. Juniper scale females are apparent on foliage as flat, round white scales, with a pale yellow centre up to 1.5mm in diameter. The males are narrower and reach 1 mm in length. It feeds on plant sap of junipers and some other conifers. The eggs of this scale insect hatch in June.

Symptoms

Juniper scale is often present on the foliage of susceptible conifers but only a problem if a heavy infestation develops when there may be yellowing and die back of the foliage. Unlike many other scale insects this species does not produce honeydew. 

There can be other reasons for brown patches in conifers including insects such as the cypress aphid.

Control

Juniper scale can be difficult to control, replacing severely infested plants can be considered. Only small trees can be treated and on large conifers treatment can be impossible.

Non-pesticide control

Well-tended healthy plants are usually able to tolerate infestations and do not need treatment. 

Pesticide control

  • The waxy covering produced by scales gives them some protection from insecticides and the best results are achieved by spraying against the newly hatched crawler nymphs in June
  • Complete spray coverage is essential if control is to be achieved and only trees and hedges that are small enough to be sprayed thoroughly should be treated with pesticides
  • Note that dead scales can remain firmly attached to the plants. The success of any treatment can be gauged by the extent to which new growth remains free of infestation
  • 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 scale insects. These pesticides have a very short persistence and so may require reapplication to keep scale insect nymphs 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
  • Follow label instructions when using pesticides
  • 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
  • Do not spray near plants in flower due to the danger to pollinating insects

Download

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


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