Once an uncommon glasshouse insect in Britain, fluted scale now occurs on outdoor plants in sheltered places.
Scientific name Icerya purchasi
Plants affected Citrus, Acacia, Choisya and many other mainly woody plants
Main cause A sap-sucking insect
Timing Present all year round
What is fluted scale?
Fluted scale is a sap-sucking insect that originates from Australasia but has become widespread in the warmer parts of the world, including the Mediterranean area. It is also sometimes known as cottony cushion scale, but should not be confused with cushion scale or woolly vine/currant scale. It was an uncommon insect in heated glasshouses in Britain but since the 1990s it has become established outside in sheltered places, especially in London.
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.
The adult flutted scales are flat, oval insects, 4-5mm long and reddish brown in colour. The females are usually found perched on the edge of white waxy mounds in which eggs are deposited. These egg mounds have a distinctive grooved or fluted appearance, which is unlike any other scale species found in the UK. The young nymphs are oval and brownish but have a white waxy coating. Adults and nymphs can be found together all year round on the stems and foliage. Frequent host plants are Citrus, Acacia and Choisya but it can occur on many other woody plants.
Fluted scale sucks sap from a wide range of trees and shrubs. Heavily affected plants lack vigour and can be killed. A black sooty mould may grow on the insect's sugary honeydew excrement.
When buying Citrus, Acacia or Choisya, check carefully to make sure they are free of infestation. If plants do become infested, this can be a difficult insect to eradicate.
Check susceptible plants frequently so action can be taken before a damaging population has developed. This scale insect has several generations a year and so there is no specific time when control measures may be most effective. 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. 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
- Adult scales and egg masses can be removed when seen but this may not reduce large populations
- Encourage predators in the garden, some ladybirds, parasitoid wasps and some birds will eat scale insects. In many parts of the world, an Australian ladybird known as the vedalia ladybird, Rodolia cardinalis, has been released as a biological control for fluted scale. This ladybird is not commercially available in Britain but it has been found in some parts of London. It probably arrived accidentally, along with the scale insect, on imported plants
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 fluted 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.
Shorter persistence pesticides (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.
- 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)
Fluted scale has two or three generations a year, which overlap so both nymphs and adults can be found at the same time. The adult scales are mainly found on the stems, whereas young nymphs are mainly on the underside of leaves along the leaf veins. Each egg mound can contain several hundred eggs.
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