Euonymus scale

Euonymus scale has become widespread in England and can cause severe dieback on evergreen Euonymus species.

Euonymus scale (Unaspis euonymi) on spindle (Euonymus europeus)

Quick facts

Common name Euonymus scale
Scientific name Unaspis euonymi
Plants affected Euonymus, especially Euonymus japonicus
Main cause A sap-sucking insect
Timing Present all year round

What is euonymus scale?

Euonymus scale is a small sap-sucking insect that feeds on the stems and foliage of Euonymus. It became established in Britain on the south coast of England during the 1950s. It is now found in gardens throughout Southern Britain. This insect has a soft flattened body that is covered by a shell or scale. This is one of many species of scale insects encountered by gardeners. 

Symptoms

Heavily infested plants develop a yellowish mottling on the foliage and this may be followed by extensive leaf fall and dieback.

Male and female euonymus scales differ in appearance. The males are mainly on the foliage and are covered with narrow white elongate scales that are 2mm long. The females mainly occur on the stems and are covered with blackish brown pear-shaped scales up to 3mm long.

This scale has two generations a year with nymphs present in late spring and autumn.

The most susceptible host plant seems to be Euonymus japonicus but other evergreen and deciduous spindles can also be affected. Heavily infested plants may lose most of their foliage and suffer dieback. These plants sometimes recover but replacement may be necessary.

Control

Check Euonymus plants frequently so action can be taken before a damaging population has developed. When choosing control options you can minimise harm to non-target animals by starting with the methods in the non-pesticide control section. If this is not sufficient to reduce the damage to acceptable levels then you may choose to use pesticides. Within this group the shorter persistence pesticides (that are usually certified for organic growing) are likely to be less damaging to non-target wildlife than those with longer persistence and/or systemic action.
Light infestations are of little consequence and can be tolerated, but heavy attacks can be dealt with in late spring or autumn when the more vulnerable newly-hatched scales are present. 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 scale insects

Non-pesticide control

  • Where possible tolerate populations of scale insects. Not all scale insects affect the growth of plants and so they do not necessarily require control
  • Adult scales can be removed when seen but this may not reduce large populations
  • Encourage predators  in the garden, some ladybirds, parasitoid wasps and some birds will eat scale insects. The native kidney spot ladybird, Chilocorus renipustulatus, specialises in feeding on scale insects and can naturally colonise infested plants reducing infestations 

Pesticide control

  • The best time for summer spraying is in late spring and early autumn when the more vulnerable newly hatched scale nymphs are present 
  • Organic sprays, such as natural pyrethrum (e.g. Bug Clear Gun for Fruit & Veg, Neudorff Bug Free Bug and Larvae Killer), fatty acids (e.g. Solabiol Bug Free, Doff Greenfly & Blackfly Killer) or plant oils (e.g. Vitax Plant Guard Pest & Disease Control, Bug Clear for Fruit and Veg) can give good control of scale insect nymphs. These pesticides have a very short persistence and so may require reapplication to keep scale numbers in check. Plant oil and fatty acid products are less likely to affect larger insects such as ladybird adults 
  • Plant invigorators combine nutrients to stimulate plant growth with surfactants or fatty acids that have a physical mode of action (e.g. Ecofective Bug Control, RHS Bug and Mildew Control, SB Plant Invigorator and Westland Resolva Natural Power Bug & Mildew). These are not considered organic
  • More persistent contact-action insecticides include the synthetic pyrethroids lambda-cyhalothrin (e.g. Westland Resolva Bug Killer), deltamethrin (e.g. Provanto Ultimate Fruit & Vegetable Bug Killer, Provanto Sprayday Greenfly Killer) and cypermethrin (e.g. Py Bug Killer)
  • The systemic neonicotinoid insecticide acetamiprid (e.g. Bug Clear Ultra) is also available

Follow label instructions when using pesticides. 
Plants in flower should not be sprayed due to the danger to bees and other pollinating insects
Inclusion of a pesticide product does not indicate a recommendation or endorsement by RHS Gardening Advice. It is a list of products currently available to the home gardener

 

Download

Pesticides for gardeners (pdf document)

Biology

Euonymus scale has two generations a year. The females deposit their eggs underneath their bodies. Nymphs of the first generation emerge in June and crawl over the plant in search of suitable places to feed. They reach the adult stage in mid-late summer and lay eggs that hatch in early autumn.

 

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