Brown scale
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.
Quick facts
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?
There are many types of scale insects encountered by gardeners, they are sap sucking true bugs. Brown scale lives primarily on stems and is found on a wide range of woody plants.
Symptoms
- 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
Control
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 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, but heavy attacks can be dealt with 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
Non-pesticide control
- 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
Pesticide control
The RHS believes that avoiding pests, diseases and weeds by good practice in cultivation methods, cultivar selection, garden hygiene and encouraging or introducing natural enemies, should be the first line of control. If chemical controls are used, they should be used only in a minimal and highly targeted manner.
- 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 Gun for Fruit & Veg, Neudorff Bug Free Bug and Larvae Killer), fatty acids (e.g. 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)
- A systemic containing the active ingredient Flupyradifurone (Provanto Smart Bug Killer) is available for use on ornamentals and selected edibles
- The systemic neonicotinoid insecticide acetamiprid (e.g. Bug Clear Ultra) is also available
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
Download
Pesticides for gardeners (pdf document)
Biology
- 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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