Why Does My Apricot Tree Have Powdery Mildew?

Powdery mildew on apricot trees appears as a white powdery or dusty coating on young leaves, new shoot tips and occasionally on the surface of immature fruit. Unlike most fungal diseases, powdery mildew thrives in warm, dry conditions with high humidity — it does not need free water on the leaf surface to infect, which makes it different to the shot hole and canker pathogens that are worst in wet weather. Dense canopies with poor air circulation and warm summers provide ideal conditions for its spread.

How powdery mildew spreads

The mildew fungus overwinters in dormant buds and on infected shoot tips. In spring, these infected buds produce "flag shoots" — shoots that are mildewed from the moment they emerge — which are the primary source of spores infecting the rest of the tree. Spores spread by air movement and rapidly colonise other young, soft tissues. Warm days with cool nights and periods of high humidity (not rain) are ideal for spore germination and infection.

Pruning out flag shoots

In spring, watch for shoots that emerge already covered in white powdery growth — these are the flag shoots emerging from infected buds. Removing them immediately in dry weather reduces the spore load significantly. In late summer or autumn, cut out any obviously mildewed shoot tips and dispose of them. Do not compost mildewed material — the spores can survive composting and reinfect the following season.

Improving air circulation

Dense canopies that trap warm, humid air create the perfect microclimate for mildew. Summer pruning that opens the centre of the tree and removes congested laterals reduces the humid conditions that favour the disease. This is particularly important for wall-trained trees where the canopy pressed against a wall can become very congested.

Treatment sprays

Sulphur-based fungicides or potassium bicarbonate products applied every 14 days from early spring through summer suppress powdery mildew effectively and are approved for organic use. Conventional myclobutanil-based fungicides provide stronger control if infection is severe. Apply from the moment mildew is first seen and continue through the growing season.