Soft scale

Soft scale insect is very widespread and common. It is flat, oval pale yellow/brown and feeds on a wide variety of garden and glasshouse plants. It produces large amounts of honeydew.

Soft scale on the underside of a bay leaf

Quick facts

Common name Soft scale
Scientific name Coccus hesperidum group
Plants affected A wide variety, common on citrus and bay
Main symptoms Sticky leaves and sooty mould
Caused by Sap sucking scale insects

What is soft scale?

There are many types of scale insects encountered by gardeners, they are sap sucking true bugs. Soft scale is a flat, oval, pale yellow/brown insect. The pale covering of the insect is waxy and repels liquids. The adults reach up to 4mm long, the immature (nymph) stages are much smaller. It is found near the midribs of leaves and on stems.

It produces large amounts of honeydew and breeds throughout the year. It feeds on many garden and glasshouse plants, including bay, Ficus and Citrus species, ivy and ferns.

Symptoms

Populations of soft scale are characterised by heavy deposits of sticky honeydew upon which a black non-parasitic fungus sooty mould often grows. The 4mm long pale yellow brown insects will be evident upon examination of the undersides of leaves and stems.

Control

Check susceptible plants frequently, especially citrus, 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.
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

Non-pesticide control

  • Where possible tolerate populations of scale insects
  • Consider replacing heavily affected plants, this scale insect is difficult to eliminate
  • Adult scales 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
  • The nematode Steinernema feltiae can be purchased to as a  biological control of soft scale and is available from some Biological control suppliers

Pesticide control

  • Sprays are most likely to affect the young (nymphal) stage, as this scale breeds all year round
  • 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. On edible plants make sure the food plant is listed on the label and follow instructions on maximum number applications, spray interval and harvest interval.
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

Female soft scales can lay up to 200 eggs underneath their body. These hatch into small pink crawler nymphs which move over the plant surface before settling down to feed. They are small enough to be easily blown around in wind currents and this is the main way that plants are colonised. The nymphs suck sap from the leaves and stems and, once feeding has commenced, they usually remain immobile for the remainder of their lives. 

In warm conditions breeding is continuous throughout the year.

A waxy layer is secreted over their bodies to form the scale, and this layer gives them some protection from pesticides.


Gardeners' calendar

Find out what to do this month with our gardeners' calendar

Advice from the RHS

Did you find the advice you needed?

RHS members can get exclusive individual advice from the RHS Gardening Advice team.

Join the RHS now

Get involved

The Royal Horticultural Society is the UK’s leading gardening charity. We aim to enrich everyone’s life through plants, and make the UK a greener and more beautiful place.