Scale Insects; soft scale coccidae hard scale diaspididae.
These small sap sucking insects are generally most troublesome on greenhouse and house plants, but certain species attack ornamental shrubs and trees and fruit grown outdoors.
Infestations are often first noticed when the leaves become sticky and sooty, or when the plant leaves begin to yellow and distort.
This is caused by the sticky honeydew they produce as they feed.
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Close examination of stems and the underside of the leaves may reveal the waxy brown, yellow or white scales that frequently form thick encrusting colonies.
These scales are the female insects, which remain in the same position for most of their lives.
Males are rarely seen but are often winged and midge-like in appearance.
There are two types of scale insect and these are; the soft scale insect (Coccidae) and the hard scale insect (Diaspididae).
Soft scale insects breed all year round on protected crops and produce large amounts of sugary honeydew when they feed on the plant's sap.
Hard scales lay eggs under their scales which hatch into nymphs after the female dies in early summer.
These nymphs only move short distances on a plant, but can be dispersed long distances on the wind or on the coats of animals.
Note; Check newly purchased plants thoroughly for signs of infestation.
This variety does not produce large amounts of honeydew.
Eggs are laid under the scales, and the newly hatched young scales move actively over plants and spread infestations.
Female nymphs become immobile once they find a suitable feeding site until such times as they become adults.
Control;
Prevention is often the best option.
Check plants regularly for signs of scale infestation and deal with them as soon as they appear.
Look for; leaf drop, honeydew, sooty mould, or ants feeding on the honeydew
If an infestation is in the early stages, the scales can be cleaned off using a brush and water, or just a thumbnail.
Remove and destroy any infested leaves,as these may harbour mobile juvenile scales.
Similarly, keep the area around the base of the plant/s free of plant debris
Chemical control; spray the affected plants with a natural fatty acid insecticide when the crawlers are hatching.
In heated greenhouses this can be at any time of year, but in the open and in un-heated greenhouses infestations usually occur during the summer.
Thorough spraying with a tar oil winter wash in December or January gives good control of scales on deciduous trees and shrubs, including fruit.
Biological control; use a natural predator such as chilocorus nigritus for hard scale insects, and metaphycus helvolus for soft scale insects.