In 2004 this aphid was exceptionally abundant on beech trees and hedges, but in most years it is not a major problem.
Plants affected
Common beech (Fagus sylvatica)
Symptoms
Pale yellow, sap-feeding aphids, which are covered by fluffy white fibres, form dense colonies on young shoots and the undersides of leaves.
Winged aphids, which have a bluish-white appearance when in flight, fly from infested plants in midsummer in search of other beech trees. These winged aphids are sometimes mistaken for another type of pest, known as whitefly, but whitefly do not infest beech trees and hedges in Britain.
The foliage becomes sticky with the honeydew that is excreted by the aphids and can develop sooty moulds. In heavy attacks the foliage at shoot tips is distorted and leaves may dry up.
Biology
Woolly beech aphid overwinters as eggs laid on beech twigs in autumn. The eggs hatch in April and heavy infestations can develop by late May to June. After that, infestations decline and, for the rest of summer, the pest is present as small, non-feeding nymphs. These complete their development in autumn to produce females that lay the overwintering eggs.
Control
Tall trees and large hedges cannot be sprayed effectively, so the aphid has to be tolerated in those situations. On small hedges and sapling beech trees, look for aphids on the underside of the new leaves in April and May. Treatment when the aphids are hatching will prevent a damaging infestation from building up.
The woolly coating on the aphids is water-repellent and can protect the aphids from contact sprays. A systemic insecticide, such as imidacloprid (Provado Ultimate Bug Killer) or acetamiprid (Scotts Bug Clear Ultra) will be absorbed into the foliage and kills the aphids as they feed. It is not worthwhile spraying a hedge or young tree after it has become heavily infested in mid summer. By then the feeding damage has already occurred and the infestation will have peaked and will be in decline.
There is a risk that honeybees may feed on the sugary excrement, known as honeydew, that aphids produce, and may be harmed by pesticides applied to foliage made sticky by honeydew.