Brown scale

Brown scale is a sap-sucking insect that evidence of which can be found on woody plants at any time of year, partly because old dead scales remain attached to the bark.

Brown scale on cotoneaster. Credit: RHS/Science.

Quick facts

Common name Brown scale
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. Brown scale is a sap-sucking insect that lives primarily on the stems of 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
  • Infested plants may lack vigour and, in heavy infestations, a black sooty mould can develop on the sugary honeydew that is excreted by the insects as they feed on sap and deposited on leaves and stems

Control

Light infestations are of little consequence, but heavy attacks are best dealt with in early to mid-summer when the more vulnerable newly-hatched scales are present.

Non-chemical control

Adult scale can be removed when seen but this may not reduce heavy infestations.

Chemical control

  • 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
  • Ornamental plants and some listed fruits trees such as cherry and plums can be sprayed with the systemic neonicotinoid insecticide acetamiprid (e.g. Bug Clear Ultra), provided label instructions are followed
  • Ornamentals and some plants with edible fruits such as plum, raspberry and blackcurrant can be treated with contact pyrethroid insecticides such as deltamethrin (e.g. Provado Ultimate Fruit & Vegetable Bug Killer) or lambda-cyhalothrin (e.g.  Resolva Bug Killer) or cypermethrin (e.g. Py Bug Killer Concentrate). Label instructions on suitability for particular food plants, especially maximum number of applications and harvest interval must be followed
  • Organic sprays can be sued on ornamental plants and fruit trees/bushes and include  plant oils/extracts (e.g. Vitax Organic Pest & Disease Control or BugClear for Fruit & Veg), or fatty acids (e.g. Bayer Bug free or Doff Greenfly and Blackfly Killer). Organic sprays containing natural pyrethrum (e.g. Bug Clear Gun for Fruit & Veg, ecofective Bug Killer (also contains fatty acids)), may also have some effect
  • Do not spray plants in flower due to the danger to pollinating insects
  • Inclusion of a pesticide product does not indicate a recommendation or endorsement by the RHS. It is a list of products currently available to the home gardener

Download

Pesticides for gardeners (Adobe Acrobat pdf document outlining pesticides available to gardeners)

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

Advertise here

Gardeners' calendar

Advice from the RHS

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

Discuss this

for the site or to share your experiences on this topic and seek advice from our community of gardeners.

  • Dr J R Bennett

    By Dr J R Bennett on 09/11/2014

    Scale insect? I did have a problem with soft scale which was dealt with by physical removal (meths on a swab) and acetomeprid. Now, mainly on cattleya leaves there is a sudden outbreak of a hard scale-looking problem - these are closely adherent to the leaves. What is it? What should I do? John Bennett


    0 replies

    Report

Get involved

We're a UK charity established to share the best in gardening. We want to enrich everyone's life through plants, and make the UK a greener and more beautiful place.