Powdery Mildew: Identification, Prevention, and Control

This fungal disease affects beans, clematis, dahlia, grape, hydrangea, rose, strawberry, tomato, zinnia, and trees like apple, maple, oak, peach, sycamore. Favored by moist air, shade, and poor air circulation—but needs dry leaves to establish. Symptoms: small gray/white circles on leaves, stems, flowers; progressing to powdery white distortion. Some plants tolerate it; others decline or fail to fruit. Severely disfigured flowering plants may need removal.

Prevention

• Plant resistant varieties.
• Spray plants with water jets to wash off spores.
• Avoid overcrowding for better sunlight/airflow.
• In fall, discard infected flowers, fruits, plants.

Treatments

• Sulfur may help.
• On roses/flowering plants: baking soda + summer oil spray.
• Antitranspirant sprays (for cold protection) may also prevent spore attachment by raising leaf surface temperature.

Chemical Controls

Triforine and thiophanate-methyl.