Coccidae and Diaspididae
In the garden: A wide range of shrubs and trees
Throughout UK and Europe
Around 25 species of scale insect can be found. They are easily identified by the waxy shells they produce when mature which resemble small discs or blobs on their host plants. Eggs are laid under the shell and the dust-like juveniles disperse from underneath. Scale insects are sap-sucking insects whose feeding can weaken plants. Some species will excrete honeydew on foliage, which promotes the growth of black, sooty moulds. These are known as soft scale insects whereas scale that don’t produce honeydew are known as hard scale.
Direct feeding damage will not affect most mature shrubs and trees that scale insects infest. Small shrubs and trees may be weakened though. The black sooty moulds that grow in the honeydew where soft scale insects feed, will reduce the leaf’s ability to breathe. The moulds are also unsightly.
Regularly check the shrubs and trees that are common hosts to scale. Early infestations can usually be removed by hand or wiped away with a damp cloth.
Regular washing with a hose will help to reduce scale numbers and help to remove the black sooty moulds. As a last resort, organic products containing fatty acids or plant oils/extracts are available from garden product suppliers. These will need to be applied following the label instructions.
The newly hatched juveniles are particularly susceptible to being washed off plants and will usually die on the ground. July is therefore the most appropriate month to spray affected plants with water.