Scale insects and mealybugs
Pseudococcidae, Diaspididae, Coccidae
Role in the garden
Small sap-sucking insects fixed on stems, leaves and fruit, protected by a white wax (mealybugs) or a shield (armoured scales). They weaken the plant, deposit sticky honeydew and encourage sooty mould.
Activity period
All year round under cover and indoors; May to October in the garden
Practical guide
Where to find them
House and conservatory plants (citrus, aloes, cacti), fig, olive, vine and bay in the garden; in the leaf axils, under the leaves, on young shoots and fruit. Mealybugs look like small cottony clusters, armoured scales like small brown or grey scales stuck to the bark.
Prevention
Inspect bought plants before installing them (the most frequent way in), ventilate and do not overheat conservatories, avoid excess nitrogen that softens the tissues, keep beneficials in the garden (ladybirds, lacewings) by giving up broad-action insecticides.
Early signs
Small white cottony flecks in the axils and under the leaves, or fixed scales on the stems; shiny, sticky honeydew; yellowing leaves, black sooty mould; ants running up and down the stems.
Action / control
On a few plants, remove the colonies with a cotton bud or a soft brush soaked in soapy water or diluted methylated spirit. Spray black soap (to be repeated: the young stages are the most sensitive) or an approved plant oil, which smothers the adults under their wax. In a greenhouse or conservatory, release Cryptolaemus montrouzieri or lacewings. Prune out and remove heavily infested shoots.
Sources
- RHS : Mealybug et Scale insects (rhs.org.uk)
- UC IPM, Pest Notes : Mealybugs et Scales (ipm.ucanr.edu)
- Jardiner Autrement (SNHF) : fiche Cochenilles
Favourite plants / resources
Related plant entries
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