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.
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 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.
Juniper scale can be difficult to control, consider replacing severely affected plants. Large populations 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
- Where possible tolerate populations of scale insects. Well-tended healthy plants are able to tolerate light populations of these insects and so they do not necessarily require control
- Encourage predators in the garden, some ladybirds, parasitoid wasps and some birds will eat scale insects
The RHS believes that avoiding pests, diseases and weeds by good practice in cultivation methods, cultivar selection, garden hygiene and encouraging or introducing natural enemies, should be the first line of control. If chemical controls are used, they should be used only in a minimal and highly targeted manner.
- 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. 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)
- A systemic containing the active ingredient Flupyradifurone (Provanto Smart Bug Killer) is available for use on ornamentals and selected edibles
- The systemic neonicotinoid insecticide acetamiprid (e.g. Bug Clear Ultra) is also available
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
Pesticides for gardeners (pdf document)
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