Wisteria scale of wisteria

Disease Information

Wisteria scale

Symptoms and damage

Wisteria scale is a sap-sucking insect that mainly occurs on wisteria but also infests some Acer and Prunus species. Scale insects are soft-bodied insects that are covered by a hard shell or scale when mature. At up to 10mm in diameter wisteria scale is substantially larger than most other scale insects.

The mature scales are found in late spring on the stems of wisteria and other host plants. The shell or scale that covers the insect and its eggs is blackish brown with a whitish dusting. It has a circular base and hemispherical shape.  Wisteria scale can be up to 10mm in diameter, and it is substantially larger than most other scale insects. The immature scales are less convex and are pale brown with pinkish-white encrustations that resemble sugar grains. The wisteria scale can develop very heavy infestations and stems can become thickly encrusted with scales.  Such infestations can make the plant lack vigour and die back.


Wisterias are often not easy to spray because of their size. It is also difficult to spray a plant thoroughly when it is growing against a wall. It is usually not worthwhile spraying if the pest is brown scale. Wisteria scale is potentially a damaging and may need treatment.

Chemical control

·         The best time to control scale insects is when the more vulnerable newly hatched scale nymphs are present.  For wisteria scale, this is in late May-June

·         Organic pesticides, such as fatty acids (e.g. Bayer Bug Free, Doff Greenfly and Blackfly Killer) or plant oils and extracts (e.g. Vitax Organic Pest and Disease Control) will give some control of newly hatched scales but several thorough applications will be required

·         Because of the difficulty of spraying the far side of wall-grown plants, short persistence contact sprays will miss many of the scale nymphs. Some longer lasting contact sprays include those containing deltamethrin (e.g. Bayer Provado Ultimate Bug Killer), lambda-cyhalothrin (e.g. Westland Resolva Bug Killer) or cypermethrin (e.g. Py Bug Killer) Systemic insecticides, such as acetamiprid (e.g. Bug Clear Ultra) may be more effective, this is absorbed into the plant tissues and taken up by the scales when they feed

·         Note that dead scales can remain firmly attached to the stems.  The success of any treatment can be gauged by the extent to which new growth remains free of infestation

·         Plants in flower should not be sprayed due to the danger to pollinating insects


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