A wide range of ornamental plants and fruit trees grown out of doors can be attacked. Several species of scale insects are confined to plants growing in glasshouses or other sheltered places.
Scales or shell-like bumps can be seen on stems and the underside of leaves. Heavy infestations may result in poor growth. Some species of scale insect produce a sticky liquid called honeydew that is excreted by the scales and is deposited on the foliage. Under damp conditions this can be colonised by a black non-parasitic fungus known as sooty mould.
Chemical control Deciduous fruit trees and roses can be treated with Growing Success Winter Wash on a mild dry day during December to control the over wintering scale nymphs. Ornamental plants in leaf can be sprayed with imidacloprid (Provado Ultimate Bug Killer), which is available as a spray concentrate. Ornamental plants and some fruits (see product label) can be sprayed with another systemic insecticide thiacloprid (Provado Ultimate Bug Killer Ready To Use).
The shell or scale protects these insects from insecticides, so spraying is more effective against the newly hatched nymphs. With scales on outdoor plants there is usually one generation a year and the eggs hatch in late June-July.
Scales in glasshouses or on houseplants breed throughout the year so all stages in the life cycle may be present at the same time. Scale insects can remain attached to the plant long after they are dead but new growth should be free of scales once they have been brought under control. Organic controls These include fatty acids (Natures Answer Natural Fungus and Bug Killer) or plant oils and extracts (Growing Success Fruit & Veg Bug Killer). These pesticides have very little persistence and so may need several applications during the scale’s egg-hatching period, but they can be used on fruit trees and bushes.
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