Hazel powdery mildew

Hazel powdery mildew (Phyllactinia corylea) is a fungal pathogen classified within the Ascomycota division. It is a well-known obligate parasite that specifically targets the foliage of various woody plants, including hazel, birch, oak, and other deciduous species, causing a distinctive powdery mildew disease that impacts plant physiology.

The disease primarily manifests on the undersides of leaves as a thin, white mycelial growth. As the fungus matures, it produces small, globose fruiting bodies called cleistothecia, which are initially yellowish but turn black, serving as the overwintering stage for the pathogen on fallen leaves or bark crevices.

The life cycle begins in spring when ascospores are released from cleistothecia during damp weather, infecting emerging foliage. Throughout the summer, the fungus reproduces asexually via conidia, which are easily disseminated by wind to neighboring plants, causing rapid secondary infections across nurseries and forest stands.

Environmental conditions significantly influence the development of Phyllactinia corylea. The pathogen thrives in moderate temperatures and high humidity levels. Cultural factors such as high-density planting, lack of canopy airflow, and excessive nitrogen fertilization can exacerbate the spread of the disease by weakening the host plants.

The impact of this disease includes premature senescence, reduced photosynthetic efficiency, and significant aesthetic damage to ornamental trees. Effective management involves a combination of sanitation—specifically removing infected leaf litter—and chemical interventions, such as applying fungicides containing sulfur, triazoles, or strobilurins during the early stages of symptom appearance.

• Remove and destroy fallen leaves to reduce primary inoculum.
• Prune branches to improve airflow within the canopy.
• Apply preventative fungicides when conditions are conducive to infection.
• Monitor host trees during the late spring and summer months.