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.
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?
Scale insects are sap sucking true bugs belonging to several families in the Hemiptera. Typically the adults are immobile having a flattened or raised appearance, with no visible legs. They often look like a ‘scale’ on a leaf or stem, many species produce a white wax often covering egg masses. There are more than 100 species found in Britain, 26 of which have been introduced. More than 25 species can be found in gardens or on houseplants.
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.
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 using the methods in the non-pesticide section below. Pesticide treatments are likely to kill natural enemies and are only likely to be successful if the entire plant can be reached.
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.
- 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 as a biological control of soft scale and is available from some Biological control suppliers. Nematodes have the potential to infect non-target animals. They should therefore be used with care and only when there is a specific problem to treat
The RHS recommends that you don't use pesticides. Most pesticides (including organic types) reduce biodiversity, including natural enemies, impact soil health and have wider adverse environmental effects.
Where you cannot tolerate soft scale, manage them using the information above as your first course of action.
Pesticide treatments are likely to kill natural enemies and so reduce the likelihood of natural control and can lead to resurgence of the target animal.
The shorter persistence pesticides (that are usually certified for organic growing) are likely to be less damaging to non-target wildlife.
The pesticides listed are legally available in the UK. This information is provided to avoid misuse of legal products and the use of unauthorised and untested products, which potentially has more serious consequences for the environment and wildlife than when products are used legally.
Always follow the instructions on the products. For edible plants, make sure the food plant is listed on the label and follow instructions on maximum number of applications, spray interval and harvest interval.
Homemade products are not recommended as they are unregulated and usually untested.
Be aware that products such as Neem oil are not registered for use in the UK and we cannot advise on their use.
Plants in flower must not be sprayed due to the danger to bees and other pollinating insects.
- 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 Ultra 2, Neudorff Bug Free Bug and Larvae Killer) or plant oils (e.g. Vitax Plant Guard Pest & Disease Control, Bug Clear 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 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 and SB Plant Invigorator). These are not considered organic
- Further information about the use of pesticides available for management of scale is available on the pesticides for gardeners leaflet
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.
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