Hemispherical scale

Small brown 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)

Quick facts

Common Name Hemispherical scale
Scientific Name Saissetia coffeae
Plants Affected Various glasshouse plants
Main Symptom Brown scale insects 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, the adults are usually immobile and shell like.  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

Hemispherical scale 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
Check susceptible plants frequently so action can be taken before a damaging population has developed. When choosing control options you can minimise harm to non-target animals by starting with the methods in the non-pesticide control section. If this is not sufficient to reduce the damage to acceptable levels then you may choose to use pesticides. Within this group the shorter persistence pesticides (that are usually certified for organic growing) are likely to be less damaging to non-target wildlife than those with longer persistence and/or systemic action.
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

Non-pesticide control

  • Where possible tolerate populations of scale insects. Not all scale insects affect the growth of plants and so they do not necessarily require control
  • Adult scales can be removed when seen but this may not reduce large populations
  • Encourage predators in the garden, some parasitoid wasps that affect these scale can be found indoors
  • The nematode Steinernema feltiae can be purchased to as a  biological control of hemispherical and is available from some Biological control suppliers
 
 

Pesticide control

  • Organic sprays, such as natural pyrethrum (e.g. Bug Clear Gun for Fruit & Veg, Neudorff Bug Free Bug and Larvae Killer), fatty acids (e.g. Solabiol Bug Free, Doff Greenfly & Blackfly Killer) or plant oils (e.g. Vitax Plant Guard Pest & Disease Control, Bug Clear for 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 and fatty acid 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, SB Plant Invigorator and Westland Resolva Natural Power Bug & Mildew). These are not considered organic
  • More persistent contact-action insecticides include the synthetic pyrethroids lambda-cyhalothrin (e.g. Westland Resolva Bug Killer), deltamethrin (e.g. Provanto Ultimate Fruit & Vegetable Bug Killer, Provanto Sprayday Greenfly 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
Plants in flower should not be sprayed due to the danger to bees and other pollinating insects
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
 
 

Downloads

Pesticides for gardeners  (pdf document)

Biological control suppliers (pdf document)

Biology

Hemispherical scale insects 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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