Why is my peach tree bark damaged on the sunny side?

Dead, cracked, or discoloured bark on the south or south-west side of a peach tree trunk — while the rest of the bark appears healthy — is a condition called sunscald, also known as southwest disease or winter sunburn. It is a physical injury caused by extreme temperature fluctuations during winter, not by a pathogen, though secondary fungal and bacterial infections can follow the initial damage.

How sunscald happens

On clear, cold winter days, winter sunlight can heat the south-facing trunk bark to temperatures 10–15°C above ambient — warm enough to trigger the bark cells to resume metabolic activity. When the sun sets or cloud covers the sky, the bark temperature plummets back to air temperature within minutes. This rapid freeze-thaw cycle kills the bark cells on the sunlit side. Damage is most severe on young trees with thin bark and on trees growing in a continental climate with cold bright winters.

Recognising sunscald damage

Initially, the affected area may appear perfectly normal. By late winter or early spring the damaged bark begins to crack, peel, and discolour — first turning orange-brown, then drying to a grey-black. The bark beneath feels dry and papery rather than firm and moist. The dead zone is typically elongated vertically on the south or south-west facing side of the trunk, distinguishing it from bacterial canker which tends to be more circular and oozes gum.

Preventing sunscald with reflective wraps

Wrapping the trunk with light-coloured tree guards — white plastic spiral wraps or natural hessian — from October to April reflects winter sunlight and prevents the trunk from absorbing enough heat to warm up. Reflective tree wraps work by keeping the bark at a more uniform, cool temperature rather than allowing the sunlight-driven temperature swings. Remove wraps each spring to prevent moisture buildup and beetle damage beneath them.

Tree whitewash

Painting the trunk with diluted white latex paint (1 part paint to 1 part water) is a traditional and effective method used widely in orchards. The white surface reflects sunlight, preventing the thermal gain that causes freeze-thaw damage. Apply from the soil line up to the first main branches in late autumn. It weathers off naturally over summer and can be reapplied each autumn indefinitely without harming the tree.

Treating existing damage

Remove loose, dead bark with a sharp knife, cutting to the margins of healthy bark. Shape the wound into a clean ellipse to encourage callus formation. Apply pruning compound or grafting wax to the exposed wood to prevent desiccation and reduce the risk of secondary bacterial canker infection entering through the damaged area. Apply trunk wrapping for the following winter to prevent the damage recurring.