Brown scale

Brown scale is a sap-sucking insect that 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 mainly 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.

Chemical control

  • Ornamental plants can be sprayed with systemic insecticides thiacloprid (e.g. Provado Ultimate Bug Killer) or acetamiprid (e.g. Bug Clear Ultra).
  • Plants with edible fruits such as plum, raspberry and blackcurrant can be treated with contact insecticides such as deltamethrin (e.g. Bayer Provado Ultimate Fruit & Vegetable Bug Killer) or lambda-cyhalothrin (e.g. Westland Resolva Bug Killer). Label instructions on suitability for particular food plants, especially maximum number of applications and harvest interval must be followed carefully. 
  • Other sprays for outdoor ornamental plants and fruit trees/bushes include those considered organic such as plant oils/extracts (e.g. Vitax Organic Pest and Disease Control or Bug Clear for Fruit & Veg), or fatty acids (e.g. Bayer Organic Bug free or Doff Greenfly and Blackfly Killer)
  • The best time for summer spraying is in early July when the more vulnerable newly hatched scale nymphs are present 
  • For scales on deciduous edible fruits, a plant oil winter wash (e.g. Growing Success Winter Tree Wash or Vitax Winter Tree Wash) can be used. This can control the overwintering scale nymphs in December-January when the plants are fully dormant
  • With grape vines, peel away the loose outer bark to expose the scales and other sheltering pests before treatment

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

Video exclusive for RHS members: expert advice on dealing with slugs and snails

Sign into the RHS website to watch video Sign in

Sign in

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 avatar

    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