Powdery mildew of barberry

Powdery mildew of barberry is caused by the fungal pathogen Erysiphe berberidis. This disease is a widespread concern for gardeners and nursery owners, as it primarily affects the foliage and young shoots of various barberry species, disrupting the normal physiological processes of the plant.

The fungus is an obligate parasite, meaning it requires living plant tissue to survive and reproduce. It is most commonly found on *Berberis vulgaris* and *Berberis thunbergii*. In severe cases, the entire surface of the leaves can become covered with a white fungal mat, leading to significant stress for the shrub.

Symptoms typically begin as small, isolated white or greyish spots on the leaf surface. As the infection progresses, these spots merge to cover large areas of the foliage, petioles, and tender green stems. The characteristic white powdery appearance is due to the mass production of conidia, which are easily detached and spread by air currents.

Development and spread of the disease are highly dependent on environmental conditions. High humidity, moderate temperatures, and lack of air circulation around the plants provide an ideal microclimate for the fungus to thrive. Dense planting schemes are particularly susceptible to rapid outbreaks during the summer months.

The harm caused by this disease manifests as stunted growth, leaf curling, premature yellowing, and leaf drop. To manage the infection effectively, one should

• remove and destroy infected plant debris
• prune the shrubs to ensure better airflow
• apply systemic fungicides containing sulfur or triazoles