In the first of an occasional series I look at pests and diseases which we gardeners battle with on a regular basis.
First Tuesday Terror is Cushion Scale.
Cushion scale is a sap-sucking insect that attacks the foliage of mainly evergreen trees and shrubs, especially camellia, skimmia, rhododendron, trachelospermum, euonymus and holly.
A coating of a black, non parasitic fungus known as sooty mould forms on the upper leaf surface, which develops during the winter and persists into the summer months. Yellow-brown, scale insects up to 3mm (1/8in) long can be seen near the veins on the undersides of the leaves. Later,
rectangular white waxy egg masses, up to 10mm (almost ½in) long and 2-3mm (1/8in) wide, are produced by the adult scales in early summer and the remains of these egg masses remain on the foliage throughout the year.
Sooty mould will slowly flake off the leaves during the summer. On small plants it can be removed by wiping the foliage with a damp cloth.
MIKE THE GARDENER 
Yes, you can continue to do what you’ve already done, or you can follow the chemical route:
Late June-July is the best time to spray the plants as that is when the more vulnerable newly-hatched scale nymphs occur
Systemic insecticides containing thiacloprid (Bayer Provado Ultimate Bug Killer concentrate), thiamethoxam* (Westland Plant Rescue Bug Killer Ornamental Plants) or acetamiprid (Scotts Bug Clear Ultra) are absorbed into the foliage and taken in by the young scales as they feed
Contact sprays containing deltamethrin (Bayer Sprayday Greenfly Killer) will also give control if applied thoroughly to the underside of leaves
Organic pesticides, based on plant oils or extracts (Growing Success Fruit & Veg Bug Killer, Vitax Organic 2 in 1 Pest and Disease Control, Scotts Bug Clear for Fruit & Veg ) or fatty acids (Bayer Organic Pest Control, Doff Greenfly and Blackfly Killer, Doff Greenfingers Organic Pest Spray ) are contact in action. They have a short persistence and thorough application to the underside of leaves is required. More frequent applications of organic pesticides may be required to deal with the scale nymphs as they hatch
Ref: http://www.rhs.org.uk
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