Wisterias are often not easy to treat 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 plant is infested with brown scale as that species of scale does not usually affect the vigour of wisteria. Wisteria scale is potentially more damaging and may need treatment.
Well-tended healthy plants are able to tolerate light infestations of this insect.
Scrape off adult scales when they are seen, this may help reduce an infestation and determine level of re-infestation but it is unlikely to eliminate it.
- 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
- 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
- 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 insect nymphs. These pesticides have a very short persistence and so may require reapplication to keep scale insects in check. Plant oil and fatty acid products are less likely to affect larger insects such as ladybird adults. This can be used on ornamental and most edible plants
- 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). These products are suitable for use on some food plants. Label instructions on suitability for particular food plants, especially maximum number of applications and harvest interval must be followed
- The systemic neonicotinoid insecticide acetamiprid (e.g. Bug Clear Ultra) is also available
- Follow label instructions when using pesticides. On edible plants make sure the food plant is listed on the label and follow instructions on maximum number applications, spray interval and harvest interval
- Do not spray plants in flower due to the danger to pollinating insects
- 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
Pesticides for gardeners (Adobe Acrobat pdf document outlining pesticides available to gardeners)