Bigleaf Hydrangeas showing powdery mildew disease | Jane Cerza, American Society for Horticultural Science (ASHS)
The woody ornamental nursery industry is an important agricultural sector in the U.S. that generates more than $5.5 billion in annual wholesale values. Among woody ornamentals, hydrangeas are valued for their large, colorful inflorescences and are widely used in commercial and residential plantings, as well as in field nurseries and greenhouses. Plant health is an important consideration in maximizing profitability. However, the health, appearance, and ornamental values of these crops are often negatively impacted by diseases, rendering them unmarketable. Powdery mildew in bigleaf hydrangea (Hydrangea macrophylla) is a destructive foliar disease.
A new study has identified effective chemical control methods for managing powdery mildew, a common fungal disease affecting bigleaf hydrangeas. The findings offer growers practical solutions to protect this popular ornamental plant and maintain its vibrant appearance in landscapes and nurseries.
Powdery mildew, caused by fungal pathogens, is a persistent challenge for bigleaf hydrangea growers. The disease manifests as white, powdery spots on leaves, reducing plant vigor and aesthetic value. This study evaluated various chemical treatments to determine the most effective options for suppressing the disease while minimizing environmental impact.
Researchers tested multiple fungicides and application schedules, revealing several products and strategies that significantly reduced powdery mildew incidence and severity. These treatments not only improved plant health but also maintained the hydrangea’s ornamental quality, ensuring its appeal for gardeners and commercial markets.
The study underscores the importance of integrated disease management, where chemical control complements other practices like proper spacing, air circulation, and resistant cultivars. By adopting these findings, growers can better protect their crops from powdery mildew and enhance the sustainability of hydrangea production.
This research was conducted by Dr. Baysal-Gurel and her team at Tennessee State University to determine the efficacy of the fungicides on powdery mildew of bigleaf hydrangea at different application rates and intervals. Plant height and width increase, defoliation percentage, defoliation progress, disease severity, and disease progress over the duration of the study were evaluated across several different experiments in both shade house and greenhouse conditions between 2022-2023.
The original ASHS press release can be found here, while the full study and results can be found on the ASHS HortScience electronic journal website.
