Fluted scale

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

Fluted scales with egg mounds on Choisya

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. It 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 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 infested plants lack vigour and can be killed. A black sooty mould may grow on the insect's sugary honeydew excrement.

Control

Non-pesticide 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 insect 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 parts of London. It probably arrived accidentally, along with the scale insect, on imported plants.

Pesticide control

  • Only plants that are small enough to be sprayed can be treated
  • Organic sprays, such as natural pyrethrum (e.g. Bug Clear Gun for Fruit & Veg, Ecofective Bug Killer), fatty acids (e.g. Solabiol Bug Free, Doff Greenfly & Blackfly Killer) or plant oils (e.g. Vitax Organic Pest & Disease Control, Bug Clear for Fruit and Veg) can give good control of scale insects. These pesticides have a very short persistence and so may require reapplication to keep scale insect nymphs in check. Plant oil and fatty acid products are less likely to affect larger insects such as ladybird adults. These organic insecticides are the only products that can be used on citrus plants where the fruits are going to be eaten
  • Ornamental plants can be treated  more persistent insecticides include the synthetic pyrethroids lambda-cyhalothrin (e.g. Westland Resolva Pest Killer), deltamethrin (e.g. Provanto Ultimate Fruit & Vegetable Bug Killer) and cypermethrin (e.g. Py Bug Killer)
  • The systemic neonicotinoid insecticide acetamiprid (e.g. Bug Clear Ultra) is also available for use on ornametal plants
  • Plants in flower should not be sprayed due to the danger to pollinating insects
  • 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

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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