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Woolly aphid is common on edible and ornamental apple trees, pyracantha and Cotoneaster horizontalis. The insects are hidden under white fluff that can be mistaken for a mould.
Woolly aphid
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Woolly aphid is an insect that, unlike most aphids, sucks sap from woody stems, rather than foliage.
Due to its conspicuous appearance, 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 should be 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 parasitic wasp called Aphelinus mali. The parasitic wasp can sometimes be found in gardens, particularly those where little 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 parasite has emerged. If the parasite is found, it can be encouraged by limiting the use of pesticides, but often the parasite only occurs in worthwhile numbers in late summer after heavy infestations of the aphid have already developed.
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.
Chemical
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 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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