Euonymus scale

Euonymus scale has become a widespread problem 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 but is now increasingly being found in gardens throughout England. This insect has a soft flattened body that is covered by a shell or scale.

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 attacked. Heavily infested plants may lose most of their foliage and suffer severe dieback. These plants sometimes recover but replacement may be necessary.

Control

Non-chemical control

There are no effective non-chemical controls for euonymus scale. It can however be predated by the kidney spot ladybird, Chilocorus renipustulatus

Chemical 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 spraying 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 pesticides, based on plant oils or extracts (e.g. Vitax Organic Pest & Disease Control Concentrate) or fatty acids (e.g. Solabiol 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
  • Contact synthetic sprays containing deltamethrin (e.g. 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
  • 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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