Why are my peach tree shoots covered in white wool?

Fluffy white or greyish cottony masses on the bark, shoots, or branch junctions of a peach tree are a reliable sign of woolly aphid (Eriosoma lanigerum) or, less commonly, mealybug. Both insects secrete a waxy, wool-like coating that protects them from most contact sprays, which makes early intervention much more effective than trying to treat a large established colony.

Identifying the pest

Woolly aphid colonies appear as compact masses of white fluff, usually at branch junctions, around pruning wounds, and in bark crevices. Beneath the wool you will find clusters of reddish-brown aphids about 2 mm long. When disturbed, the aphids drop or move slowly. Mealybugs look similar but are larger — 3–5 mm — and tend to colonise where branches fork and in bark fissures. The tell-tale test: rub the white mass between your fingers. If it smears pink-red, it is woolly aphid. Mealybug will leave a greasy smear.

Why the infestation matters

Both pests feed by inserting stylet mouthparts into the bark and phloem, extracting plant sap. Heavy infestations weaken shoots, cause galls and corky swellings in the wood, and excrete honeydew that encourages sooty mould growth. On young trees, a severe woolly aphid infestation can distort new growth and reduce vigour significantly. On established trees, the main concern is the corky swellings that develop around feeding sites — these persist long after the insects are controlled.

Mechanical removal first

In spring when colonies are newly established, a stiff brush (an old toothbrush works well) dipped in a solution of insecticidal soap or methylated spirits can scrub colonies off bark and shoots. Work around the entire tree, paying particular attention to pruning scars and branch forks. This mechanical approach directly removes insects and eggs and is safe for beneficial insects if you target the colonies specifically rather than spraying the whole tree.

Insecticidal treatments

For larger infestations, apply a fatty acid or plant-oil based spray (insecticidal soap or neem oil) directly onto the woolly masses, saturating them thoroughly. The waxy coating repels water-based sprays unless a surfactant is included. Apply in the morning or evening to avoid harming beneficial insects and repeat after seven to ten days. Avoid systemic insecticides near harvest as residues can persist in the fruit.

Biological control

The parasitic wasp Aphelinus mali is a naturally occurring enemy of woolly aphid that can be encouraged by reducing broad-spectrum insecticide use. Planting nectar-rich flowers nearby — phacelia, sweet alyssum, or dill — supports populations of this parasitoid and of ladybirds, lacewings, and other predators that also feed on the aphids and mealybugs.