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 Thuja

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 Thuja
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 that can be 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. Large populations of juniper scale often seem to develop on plants that are already suffering a lack of vigour for these other reasons.

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.

Juniper scale can be difficult to control, consider replacing severely affected plants. Large population of juniper scale often develop on plants that are already lacking vigour. Only small trees can be treated and on large conifers treatment can be impossible.
Check junipers and other susceptible conifers frequently so action can be taken before a damaging 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 the 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.
Light infestations are of little consequence and can be tolerated, but heavy attacks can be dealt with in June when the more vulnerable newly-hatched scales are present. 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 scale insects

Non-pesticide control

  • Where possible tolerate populations of scale insects. Not all scale insects affect the growth of plants and so they do not necessarily require control
  • Encourage predators  in the garden, some ladybirds, parasitoid wasps and some birds will eat scale insects

Pesticide control

  • The best time for summer spraying is in early June when the more vulnerable newly hatched scale nymphs are present 
  • 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 scale insect nymphs. These pesticides have a very short persistence and so may require reapplication to keep scale 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 (e.g. Ecofective Bug Control, RHS Bug and Mildew Control, SB Plant Invigorator and Westland Resolva Natural Power Bug & Mildew). These 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

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Pesticides for gardeners  (pdf document)


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