Brown scale

Brown scale can be found on woody plants at any time of year 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 develops on the scale's sugary excrement, which is 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

  • Spray ornamental plants with systemic insecticides thiacloprid (e.g. Provado Ultimate Bug Killer) or acetamiprid (Bug Clear Ultra). Contact insecticides such as deltamethrin (e.g. Bayer Provado Ultimate Fruit & Vegetable Bug Killer) or lambda-cyhalothrin (e.g. Westland Resolva Bug Killer). These pesticides can be used on some fruits affected by brown scale, including plum, raspberry and black currant, check the label before purchase.
  • Other treatments for outdoor ornamental plants and fruit trees/bushes include plant oils/extracts (e.g. Vitax Organic 2 in 1 Pest and Disease Control or Bug Clear for Fruit & Veg), or fatty acids (e.g. Bayer Organic Pest Control 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 is used against 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

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