Powdery mildew of crape myrtle

Erysiphe australiana is a fungal pathogen belonging to the order Erysiphales, specifically known for causing powdery mildew on crape myrtle (Lagerstroemia). This disease is a significant concern for nurseries and landscape managers, as it affects the vitality and ornamental appearance of one of the most popular flowering shrubs.

The host range of Erysiphe australiana is primarily restricted to Lagerstroemia species. The fungus establishes itself on the plant surface, primarily targeting young foliage, tender shoots, and developing flower buds. In severe cases, the infection can cover the entire canopy, leading to a stunted growth habit that persists throughout the growing season.

The disease is easily identified by the appearance of white, powdery fungal mycelium on the upper and lower leaf surfaces. As the fungal colony expands, leaves may become chlorotic, curled, and brittle before falling prematurely. Flowers often fail to open properly or dry out, which prevents the plant from producing its characteristic late-summer blooms.

Environmental conditions favoring the development of this fungus include high humidity, moderate temperatures, and lack of airflow. The pathogen thrives in shaded areas where moisture persists on foliage. Spores are primarily dispersed by wind, allowing the disease to spread rapidly across garden beds if not managed through proper sanitation and space management.

Effective management requires a multi-faceted approach. Cultural practices such as pruning to increase light penetration and air circulation are essential for reducing the humidity around the foliage. When the infection is widespread, chemical control using fungicides such as triazoles, sulfur-based compounds, or newer systemic products is recommended to suppress fungal growth and protect new, healthy tissues.

• Prune plants to improve airflow and reduce humidity.
• Remove and destroy severely infected plant debris.
• Monitor plants closely during cool, humid weather.
• Apply fungicides preventively in high-risk environments.