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.
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
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
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