Powdery mildew of privet

The disease is caused by the obligate parasite Erysiphe ligustri, an ascomycete fungus that infects the surface tissues of host plants. Unlike some generalist pathogens, this fungus specifically targets species within the Ligustrum genus, making it a recurring issue for ornamental hedges and privacy screens.

The primary hosts for this pathogen are various species of privet, with Ligustrum vulgare being particularly susceptible. The disease affects both young container-grown nursery stock and established mature shrubs in landscape settings, where high plant density often exacerbates the spread of the fungus.

Early symptoms appear as small, dusty white spots on the leaves, which quickly expand into a dense, powdery mat. As the infection progresses, leaves may become distorted, curled, or chlorotic. In severe cases, the fungus covers both leaf surfaces and tender stems, leading to stunted growth and premature leaf drop.

The development of Erysiphe ligustri is favored by moderate temperatures between 18°C and 25°C and high humidity levels. Poor airflow, often resulting from dense plantings or neglect in pruning, creates a microclimate that allows the mycelium to thrive. Spores are easily disseminated by wind and water splashes during irrigation.

The economic impact of this disease is primarily aesthetic, as it severely damages the appearance of hedges used for landscape design. Beyond the cosmetic issue, the stress of the infection weakens the shrub, making it less resilient to environmental stressors like frost and drought. Effective control is essential to maintain the long-term health of the planting.

• Ensure proper plant spacing to improve airflow through the canopy.
• Practice regular pruning to remove infested foliage and open the shrub to sunlight.
• Apply fungicides containing sulfur, tebuconazole, or other appropriate active ingredients.
• Avoid excessive nitrogen fertilization, as it promotes soft, susceptible growth.