Hydrangea scale

Hydrangea scale became established in the UK during the 1980s and has since become widespread in English gardens, it is also found in parts of Scotland and Wales.

Hydrangea scale

Quick facts

Common name Hydrangea scale
Scientific name: Pulvinaria hydrangeae
Plants affected Hydrangea, Acer sp, Prunus sp and others
Main symptoms: White oval egg masses on the stems and foliage
Most active May-August

What is hydrangea scale?

Hydrangea scale is a sap sucking insect found on hydrangeas but can also feed on many other woody plants including Acer and Prunus. Infested plants can suffer a lack of vigour caused by the insect sucking sap from the foliage and stems. It can also lead to leaf loss.

Symptoms

The immature scales are difficult to see but infestations become apparent in early summer when the mature scales deposit their eggs on the stems and leaves. You may see:

  • Eggs which are covered in white waxy fibres that form smooth, oval patches 3-4mm long. These white patches will persist on the plant long after the eggs have hatched
  • Newly hatched scales are less than 1mm long and are pale yellow
  • The mature scales are oval in shape and brown
  • Heavily infested plants lack vigour and may shed leaves and this insect can spoil the appearance of plants by the covering of white egg masses.

Control

Non-chemical control

Heavily infested plants should be removed and replacements planted in the autumn. Some manual removal of egg masses and adult scale can be attempted but may have a limited affect.

Chemical control

Control is best attempted in July when the more vulnerable scale nymphs are present. Hydrangeas can be prone to damage from sprays to the leaves, to reduce this risk avoid spraying hydrangeas in hot sunny weather or if the soil is dry.

  • Contact sprays containing deltamethrin (e.g. Bayer Sprayday Greenfly Killer),  lambda-cyhalothrin (e.g. Westland Resolva Bug Killer) or cypermethrin (e.g. Py Bug Killer) can give control if applied thoroughly to the underside of leaves 
  • The systemic neonicotinoid insecticide acetamiprid (e.g. Bug Clear Ultra) is absorbed into the foliage and taken in by the young scales as they feed
  • Organic pesticides, based on plant oils or extracts (e.g. Vitax Organic Pest & Disease Control Concentrate) or fatty acids (e.g. Bayer Bug free, Doff Greenfly and Blackfly Killer) or based on pyrethrins (e.g. Bug Clear for Fruit & Veg, Defenders Bug Killer, ecofective Bug Killer (also contains fatty acids)) can be used. These are contact in action, 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
    Note that dead scales can remain firmly attached to the plants. The success of any treatment can be gauged by the extent to which new growth remains free of infestation
  • Inclusion of a pesticide product does not indicate a recommendation or endorsement by the RHS. It is a list of products currently available to the home gardener
  • Do not spray on or near plants in flower due to the danger to pollinating insects

Download

Pesticides for gardeners (Adobe Acrobat pdf document outlining pesticides available to gardeners)

Biology

Hydrangea scale is a sap-sucking insect that develops on the underside of leaves on Hydrangea and other host plants.

There is one generation a year with young nymphs hatching from eggs in mid-summer and sucking sap from the undersides of leaves. In late summer the nymphs move to the stems where they overwinter before maturing in late spring. Eggs are deposited under a covering of white waxy fibres in early summer.

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