Hemispherical scale

Small sap sucking hemispherical scale insects can encrust the leaves and stems of a wide range of glasshouse plants.

Hemispherical scale ( Saissetia coffeae ) on Climbing fern ( Lygodium circinatum )

Hemispherical scale (Saissetia coffeae) on Climbing fern (Lygodium circinatum)

Quick facts

Common Name Hemispherical scale
Scientific Name Saissetia coffeae
Plants Affected Various glasshouse plants
Main Symptom Small brown scales on leaves and stems
Most Active year round

What is hemispherical scale?

There are many types of scale insects encountered by gardeners, they are sap sucking true bugs. Hemispherical scale is a dark brown, round, convex scale insect up to 4mm in diameter. It is found on the leaves and stems of indoor and glasshouse plants such as ferns, cycad, ornamental asparagus, Stephanotis and many others. It produces honeydew and breeds throughout the year.  

Symptoms

This scale insect rarely causes direct damage to plants. Apart from the presence of the insects the main symptom is the presence of honeydew on which sooty mould can grow.

It can appear similar to other diaspid scales. 

Control

Hemispherical scale insects can be difficult to control; replacing severely infested plants should be considered.

Non-pesticide control

Well-tended healthy plants are able to tolerate infestations. Physically squashing or removing scales may control light infestations.

Parasitic wasps (Metaphycus helvolus, Encyrtus spp. and Encarsia citrina) are sometimes available for control of hemispherical scale in glasshouses from biological control suppliers. A nematode control Steinenema feltiae, is also sometimes available.

Pesticide control

  • The waxy covering produced by scales gives them some protection from insecticides and the best results are achieved by spraying against newly hatched crawlers
  • 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 infestation
  • 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 products can be used on edible citrus
  • 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
  • Follow label instructions when using pesticides
  • 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
  • Do not spray on or near plants in flower due to the danger to pollinating insects

Downloads

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

Biological control suppliers (Adobe Acrobat pdf)

Biology

Hemispherical scale feed by sucking sap from the leaves and stems of various glasshouse plants. Scales are named for the waxy shell-like casing which covers most of their body. When mature, the females lay their eggs under the protection of this shell.

All hemispherical scales are female and reproduction is continuous throughout the year and entirely parthenogenetic. The eggs hatch into small active nymphs, known as crawlers, which wander over the plant surface until they find a suitable place to feed. They then become immobile and begin to produce their characteristic scale covering.

Infestations of scale insects are spread by the crawler stage, which may travel quite long distances before stopping to feed, and which can be spread by wind currents.


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