Heavy cushion scale populations can result in the foliage of camellia, holly, rhododendron, Trachelospermum and some other evergreen plants being covered in sooty mould during the early months of the year.
Scientific name Pulvinaria floccifera
Plants affected Camellia, Ilex (holly), Euonymus japonicus, Rhododendron, Trachelospermum, Taxus (yew) and some other evergreen shrubs
Main symptoms Black sooty mould on the upper leaf surface in winter-spring; scale insects and white egg masses on the underside of leaves in spring and summer
Most active All year round
What is cushion scale?
Scale insects are sap sucking true bugs belonging to several families in the Hemiptera. Typically the adults are immobile having a flattened or raised appearance, with no visible legs. They often look like a ‘scale’ on a leaf or stem, many species produce a white wax often covering egg masses. There are more than 100 species found in Britain, 26 of which have been introduced. More than 25 species can be found in gardens or on houseplants.
Cushion scale is a sap-sucking insect that feeds on the foliage of mainly evergreen trees and shrubs, especially camellia, rhododendron, Trachelospermum, Euonymus japonicus and holly.
- The scale does not usually affect the vigour or flowering of it's host plants, it does however produce a sticky honeydew excrement
- A heavy coating of a black, non-parasitic fungus known as sooty mould can grow on honeydew on the upper leaf surface. This develops over the winter months and can persist into the summer
- Yellowish-brown, oval scale insects up to 3mm (1/8in) long can be seen near the veins on the undersides of the leaves
- Rectangular white waxy egg masses, up to 10mm (almost ½in) long and 2-3mm (1/8in) wide, are produced by the adult scales in spring and early summer. The remains of these egg masses can persist on the foliage throughout the year
Apart from the presence of honeydew and sooty mould cushion scale does not appear to adversely affect the vigour of its host plants and so can be tolerated.
Check susceptible plants frequently from late winter onwards for sooty mould so action can be planned later in the season. When choosing control options you can minimise harm to non-target animals by using the methods in the non-pesticide section below. Pesticide treatments are likely to kill natural enemies and are only likely to be successful if the entire plant can be reached.
Light infestations are of little consequence and can be tolerated, but heavy attacks can be dealt with in early to mid-summer 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. Sooty mould will gradually flake off the leaves during the summer.
- 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
- On small plants sooty mould can be removed by wiping the foliage with a damp cloth
- Adult scales and egg masses can be removed when seen (spring and summer) but this may not reduce large populations
- Encourage predators in the garden, some ladybirds, parasitoid wasps and some birds will eat scale insects
The RHS recommends that you don't use pesticides. Most pesticides (including organic types) reduce biodiversity, including natural enemies, impact soil health and have wider adverse environmental effects.Where you cannot tolerate cushion scale, manage them using the information above as your first course of action.
Pesticide treatments are likely to kill natural enemies and so reduce the likelihood of natural control and can lead to resurgence of the target animal.
The shorter persistence products (that are usually certified for organic growing) are likely to be less damaging to non-target wildlife.
The pesticides listed are legally available in the UK. This information is provided to avoid misuse of legal products and the use of unauthorised and untested products, which potentially has more serious consequences for the environment and wildlife than when products are used legally.
Always follow the instructions on the products. For edible plants, make sure the food plant is listed on the label and follow instructions on maximum number of applications, spray interval and harvest interval.
Homemade products are not recommended as they are unregulated and usually untested.
Be aware that products such as Neem oil are not registered for use in the UK and we cannot advise on their use
Plants in flower should not be sprayed due to the danger to bees and other pollinating insects.
- The best time for spraying is in June and early July when the more vulnerable newly hatched scale nymphs are present
- Organic sprays, such as natural pyrethrum (e.g. Bug Clear Ultra 2, Neudorff Bug Free Bug and Larvae Killer) or plant oils (e.g. Vitax Plant Guard Pest & Disease Control, Bug Clear 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 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 and SB Plant Invigorator). These are not considered organic
- Further information about the use of pesticides available for management of scale is available on the pesticides for gardeners leaflet
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)
- There is one generation of cushion scale a year with eggs hatching in late June-July
- The scales suck sap and excrete a sugary honeydew that coats the upper leaf surface, allowing sooty moulds to develop, especially during the winter
- The level of infestation can vary considerably from year to year. In mild wet winters, populations of overwintering nymphs may be reduced by a (insect pathogenic) fungal infection
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