Woolly Beech Aphid

Written by melissa monks
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Woolly Beech Aphid
Aphids feed on the sap in leaves. (Jupiterimages/Photos.com/Getty Images)

Beech trees are generally free of pests but they do have one insect that plagues them -- the woolly beech aphid. Infested trees are always frustrating for gardeners. The best weapon in any tree owner's arsenal is knowledge. Learning about its life cycle and habits can help you beat this bug and take your beech tree back.


The woolly beech aphid is found in both the eastern and western parts of the United States. Its only host is the European birch, Fagus sylvatica. They are soft-bodied insects covered in a white, waxy substance that gives them a cottony appearance. This waxy substance helps protect them from predators and pesticides.

Life Cycle

Aphids can produce many generations during a summer growing season. Woolly aphids generally produce wingless offspring asexually throughout the summer. In early fall they produce winged females who fly to a new host tree and lay eggs that will overwinter on the tree. In spring, they'll hatch and produce two generations before producing more winged females to fly and find another host.


Damage is typically cosmetic and doesn't threaten the life of the tree. When large populations of woolly beech aphids are present cast off skins left behind by moulting nymphs can give leaves a white appearance. These pests can generally be found congregating on the undersides of leaves as they feed on the sap within them. As they feed aphids leave behind a sugary excretion called honeydew. Honeydew can attract wasps, bees or ants to the tree and is also an excellent growing medium for sooty mould. Large amounts of sooty mould can turn leaves black and impede photosynthesis.


Large, healthy trees can usually support a summer aphid infestation and control isn't necessary, according to the University of Illinois Extension. Aphids can be knocked off the tree with a strong jet of water. Insecticidal soaps or products containing acephate or imidacloprid are most effective if you feel pesticides are warranted.

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