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 )

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 infests the stems and foliage of Euonymus. It became established in Britain on the south coast of England during the 1950s. It spread along the south and east coasts and is now found in gardens throughout England. This insect has a soft flattened body that is covered by a shell or scale. There are many types 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.

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

Non-pestcide control

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 to control scale insects is when the more vulnerable newly hatched nymphs are present. As this insect has two generations a year, the best times for treatment are in June and early September. Dead scales often remain attached to the plant but new growth should stay clean if the treatment has been successful.

  • Organic sprays, such as natural pyrethrum (e.g. Bug Clear Gun for Fruit & Veg, Ecofective Bug Killer), fatty acids (e.g. Solabiol Bug Free, Doff Greenfly & Blackfly Killer) or plant oils (e.g. Vitax Organic Pest & Disease Control, Bug Clear for Fruit and Veg) can give good control of scale insects. These pesticides have a very short persistence and so may require reapplication to keep scale insect nymphs in check. Plant oil and fatty acid products are less likely to affect larger insects such as ladybird adults 
  • More persistent insecticides include the synthetic pyrethroids lambda-cyhalothrin (e.g. Westland Resolva Pest Killer), deltamethrin (e.g. Provanto Ultimate Fruit & Vegetable Bug 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
  • 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 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

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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