Why Is My Apple Tree Covered in Woolly White Patches?

White, fluffy, cotton-like tufts clinging to the bark of apple branches — particularly in the crevices, at pruning wounds and on young shoots — are colonies of woolly aphid (Eriosoma lanigerum). The white material is a protective waxy secretion produced by the insects themselves, not mould or disease. If you press the patch with a finger, it smears a pink or reddish colour — that is the body fluids of the aphids beneath the wool. Woolly aphid is a common and persistent apple pest that causes both direct damage and creates entry wounds for canker.

How woolly aphid damages apple trees

Woolly aphids feed by inserting their mouthparts into the bark and drawing sap from the phloem. At feeding sites on young shoots and branches, they stimulate the formation of woody galls — swollen, distorted growths on the affected wood. These galls weaken the branch structure and provide ideal overwintering sites for the next generation. More seriously, the feeding wounds created in bark provide direct entry points for canker fungus, and woolly aphid-infested trees in canker-prone areas tend to develop much more severe canker than clean trees.

Treatment options

For accessible colonies on branches, scrub with a stiff brush dipped in a strong insecticidal soap solution — this physically removes the aphids and the wool covering. A direct, high-pressure spray of insecticidal soap or pyrethrum to the colony kills the aphids on contact; the waxy wool reduces penetration, so thorough coverage and repeat applications are needed. In summer, the parasitic wasp Aphelinus mali is a natural enemy that can reduce woolly aphid populations significantly — avoid broad-spectrum insecticides that kill this beneficial predator.

Winter treatment

Woolly aphid overwinters as eggs and nymphs in bark crevices and galls. A winter wash of plant oil emulsion applied to the whole tree in December to January kills overwintering eggs and nymphs, significantly reducing the following season's population. Clean out all debris from bark crevices before spraying.

Resistant rootstocks

Apple trees grafted onto MM106 or MM111 rootstocks have genetic resistance to woolly aphid, making infestation far less severe than on susceptible M9 or M26 rootstocks. If woolly aphid is a persistent major problem, the rootstock used at planting is a significant factor.