Fluted scale

Once an uncommon glasshouse pest in the UK, fluted scale now occurrs on outdoor plants in sheltered places.

Fluted scales with egg mounds on Choisya

Quick facts

Common name Fluted scale
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. In the past is was an uncommon problem heated glasshouses in the UK but since the 1990s it has become established outside in sheltered places, especially in London.

Symptoms

The adults are flat, oval insects, 4-5mm long and reddish brown in colour. The females are 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 also attack many other woody plants.

Fluted scale sucks sap from a wide range of trees and shrubs. Heavily infested plants lack vigour and can be killed. A black sooty mould may grow on the insect's sugary excrement.

Control

Non-chemical control

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 pest to eradicate. On small plants, look for and remove the scales and their egg mounds before eggs hatch.

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 the UK but it has been found in some London gardens. It probably arrived accidentally, along with the scale insect, on imported plants.

Chemical control

Plants that are small enough to be sprayed can be treated with deltamethrin (e.g. Bayer Sprayday Greenfly Killer), lambda-cyhalothrin (e.g. Westland Resolva Bug Killer) or the neonicotinoid insecticide acetamiprid (e.g. Bug Clear Ultra). On citrus plants where the fruits are going to be eaten, only organic insecticides, such as natural pyrethrum (e.g. Bug Clear Gun for Fruit and Veg, Defenders Bug Killer), plant oils (e.g. BugClear for Fruit & Veg Gun!) or fatty acids (e.g. Bayer Bug Free) can be used. Several thorough applications will be needed with organic products to control the nymphs as they hatch.

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.

Plants in flower should not be sprayed due to the danger to pollinating insects.

Download

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

Biology

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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