Advice
RHS Help & Advice
Brown scale (Parthenolecanium corni)
Plants
affected
Many woody plants, especially those growing in the shelter of a wall or fence. They include Ceanothus, Cotoneaster, Cytisus, Weigela, Wisteria, roses, and bush and cane fruits. In glasshouses grapevines, peaches and nectarines may be affected.
Symptoms
Convex, oval, dark brown shells, 3-6mm long occur on the woody stems. Plants may suffer from a lack of vigour and in heavy infestation a black sooty mould develops on the scale's sugary excrement deposited on the leaves and stems.
Cause
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 about 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.
Control
Light infestations are of little consequence, but heavy attacks can be controlled in early to mid-summer when the more vulnerable newly hatched scales are present. Spray ornamental plants with Provado Ultimate Bug Killer concentrate (imidacloprid), Provado Ultimate Bug Killer Ready To Use (thiacloprid) or Scotts Bug Clear Ultra concentrate (acetamiprid). Alternative treatments for outdoor ornamental plants and fruit trees/bushes are plant + fish oils (Vitax Organic 2 in 1 Pest and Disease Control or Scotts Bug Clear for Fruit & Veg) or fatty acids (Bayer Organic Pest Control, Doff Greenfly and Blackfly Killer or Greenfingers Organic Spray).
For scales on deciduous edible fruits a plant oil winter wash (Growing Success Winter Tree Wash) can be used. This is used against the overwintering scales 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.