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Woolly aphid is common on edible and ornamental apple trees, pyracantha and Cotoneaster horizontalis. The insects produce a white waxy 'fluff' that can be mistaken for a mould.
Woolly aphid
Aphids, also known as greenfly and blackfly, are sap-sucking insects. Woolly aphid is black aphid that sucks sap from woody stems and covers itself in a white waxy secretion.
Woolly aphid is usually easy to spot;
On small trees with light infestations, it is possible to control woolly aphid by scrubbing the aphid colonies with a stiff-bristled brush. This is best done in spring or early summer before an extensive infestation has built up.
Woolly aphid has a number of natural enemies which help to keep it in check, although they are rarely effective enough to prevent damage occurring. They are eaten by some ladybirds, lacewings and hoverfly larvae, and they are also attacked by a parasitoid wasp called Aphelinus mali. The parasitoid wasp can sometimes be found in gardens, particularly those where little pesticide spraying is done. It is fairly easy to recognise the parasite's presence, as parasitised aphids stop producing wax and become black. A circular hole can sometimes be seen in the aphid's upper surface where the adult parasitoid wasp has emerged. If the parasitoid is found, it can be encouraged by limiting the use of pesticides.
Research indicates that earwigs on fruit trees can reduce aphid numbers and on fruit trees they do not cause damage. Providing shelters such as flower pots loosely stuffed with hay in trees can help increase numbers.
Pesticides for gardeners (Adobe Acrobat pdf document outlining pesticides available to gardeners)
Woolly aphid overwinters on its host plants as nymphs that hide in cracks in the bark or in crevices around old feeding areas. During the winter months the aphids do not produce the waxy material that gives them the characteristic woolly coating in spring and summer.
In spring, the aphids become active again, mainly around old pruning cuts or other places on the trunk or larger branches where the bark is thinner. They begin sucking sap from beneath the bark, and start secreting the fluffy ‘wool’.
Infestations reach a peak in mid- to late summer, when the aphids spread onto the younger shoots. Chemicals secreted into the plant as the aphids feed induce lumpy growths in the bark, especially on the younger shoots.
In mid-summer, winged forms of the aphid develop and these will fly off in search of new host plants.
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