Brown scale is a sap-sucking insect, evidence of which can be found on woody plants at any time of year, partly because dead scales remain attached to the bark.
Scientific name Parthenolecanium corni
Plants affected Many woody plants, including Ceanothus, Cotoneaster, Cytisus, Weigela, Wisteria, roses, plums and bush and cane fruits. In glasshouses grape vines, peaches and nectarines may be affected
Main symptoms Brown, oval convex shell-like objects on the branches
Most active All year
What is brown 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.
Brown scale lives primarily on stems and is found on a wide range of woody plants.
- Convex, oval, dark brown 'shells', 3-6mm long (1/8in to 1/4in), occur on the woody stems
- Heavily affected plants may lack vigour and a black sooty mould can develop on the sugary honeydew that is excreted by the insects as they feed on sap
Check susceptible plants frequently from spring onwards so action can be taken before a damaging infestation 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 populations are of little consequence and can be tolerated, if there are large numbers they can be managed in early to mid-summer when the more vulnerable newly-hatched scales are present. 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. Well-tended healthy plants are able to tolerate light populations of these insects and so they do not necessarily require control
- Adult scales and egg masses 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 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 brown 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 products (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 are not registered for use in the UK and we cannot advise they are used.
- For scales on deciduous plants including edible fruits, a plant oil winter wash (considered organic e.g. Growing Success Winter Tree Wash) can be used. This can control the overwintering scale nymphs in December-January when the plants are fully dormant
- The best time for summer spraying is in early July when the more vulnerable newly hatched scale nymphs are present
- With grape vines, peel away the loose outer bark to expose the scales and other sheltering pests before treatment
- 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
Pesticides for gardeners (pdf document)
- These sap-sucking insects are protected by their shells, beneath which the mature females lay eggs in early summer
- The eggs hatch in late June-July and the young scales crawl around, but soon settle down to suck sap from the undersides of the leaves
- In late summer they move to the bark, where they overwinter as reddish-brown nymphs about 1mm in length
- They complete their development in the following spring
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