Why Does My Cherry Tree Have Powdery Mildew?

A fine white or grey powdery coating on young cherry leaves and shoot tips — particularly on the newest growth at the tips of the branches — is powdery mildew. On cherry trees, powdery mildew rarely threatens the tree's survival, but it weakens young growth, causes leaves to cup and distort, and in severe cases can reduce the tree's ability to form flower buds for the following season. Understanding what drives it helps you reduce its impact without resorting to sprays.

What is powdery mildew on cherry trees?

Cherry powdery mildew is caused by the fungus Podosphaera clandestina. Unlike most plant pathogens, it does not require water on the leaf surface to infect — it spreads by airborne spores and establishes most readily in warm, dry conditions with low air movement. Young, rapidly growing tissue is most susceptible: the fungus feeds on the tender surface cells of expanding leaves and shoot tips, and cannot penetrate the toughened cells of mature leaves as effectively. Infections visible in summer typically overwinter in dormant buds and reinitiate from the same buds in spring.

Recognising the symptoms

Look for white or pale grey powdery patches on the upper surface of young leaves, shoot tips and occasionally on very young fruit. Affected leaves often cup upward and inward, and may fail to expand fully. In heavy infections, shoot growth is stunted and the whole tip may die back. The powdery coating can be rubbed off with a finger, distinguishing it from the structural silvering of silver leaf disease, which cannot be wiped away.

Pruning to improve air circulation

Dense, overcrowded canopies with crossing and inward-growing branches trap warm, humid air and create the low-air-movement conditions that favour mildew spread. Summer pruning — removing the central portion of crossing shoots, opening the centre of the canopy — is the single most effective cultural control. A well-structured, open cherry canopy has significantly lower mildew pressure than an unpruned, congested one.

Avoiding excess nitrogen

High-nitrogen feeding promotes the soft, rapidly growing shoot tissue that is most susceptible to mildew infection. If your tree produces long, lush extension growth and mildew is a regular problem, reduce nitrogen inputs and replace them with a balanced or potassium-biased fertiliser. Avoid feeding in late summer, which stimulates growth too late in the season to harden before autumn.

Removing infected tips

Cutting back affected shoot tips to healthy tissue and removing them from the garden in summer reduces the available inoculum for the following season. Do not compost infected material. This is particularly worth doing in late summer on the worst-affected shoots.