Powdery mildew
Erysiphe cruciferarum
What is Powdery mildew (Erysiphe cruciferarum)?
Powdery mildew, scientifically known as Erysiphe cruciferarum, is a global fungal disease affecting plants in temperate regions. It forms a white or grayish powdery coating on leaves, stems, and flowers, causing stunted growth and distortion. This disease poses a significant threat to crops like cabbage, broccoli, Brussels sprouts, cauliflower, radicchio, radishes, turnips, and other cruciferous vegetables, as well as various ornamental plants.
How does Powdery mildew (Erysiphe cruciferarum) occur?
Powdery mildew fungi form thin layers of mycelium on plant surfaces, creating a white, powdery appearance due to abundant spores. Wind disperses these chain-like spores, distinguishing them from downy mildew. Powdery mildew can germinate and infect plants without free water, although prolonged moisture inhibits or kills certain spores. Moderate temperatures (60°F to 80°F) and shade promote its development, while extreme heat (above 90°F) and direct sunlight hinder it. Understanding these factors is crucial for managing powdery mildew infestations.
Symptoms
1 - Effects on Plants
• The white powdery coating hampers photosynthesis, impacting plant growth and vigor. • Stunted growth and distortion: Infected plants may exhibit stunted growth and distorted appearance, affecting crop yields and quality.
2 - Soil Health
• Powdery mildew does not directly affect soil properties or fertility. • Severe infections weaken plants, making them more vulnerable to other diseases or stresses, indirectly affecting soil health. • Infected plant debris on the soil surface can create a favorable environment for other fungal pathogens or pests.
Solutions
1 - Plant Management Strategies
• Choose Resistant Varieties: Opt for vegetable varieties that are resistant to powdery mildew to reduce the risk of infection. • Proper Spacing: Provide sufficient spacing between plants to ensure good air circulation and reduce humidity levels. • Sunlight Exposure: Plant in sunny areas to promote dry conditions and discourage powdery mildew growth.
2 - Cultural Practices
• Watering Techniques: Avoid overhead watering to keep foliage dry; instead, water at the base of plants. • Balanced Fertilization: Apply balanced fertilizers and avoid excessive nitrogen, which can promote susceptible foliage. • Pruning and Sanitation: Regularly remove and destroy infected plant parts to prevent the spread of spores.
3 - Biological Fungicides and Horticultural Oils
• Biological fungicides like Serenade contain beneficial microorganisms that destroy fungal pathogens. • Serenade utilizes Bacillus subtilis, a bacterium that helps prevent powdery mildew infection. • Although nontoxic to people, pets, and beneficial insects, Serenade may be less effective than oils or sulfur in controlling powdery mildew. • Horticultural Oils: Saf-T-Side Spray Oil, Sunspray Ultra-Fine Spray Oil, and jojoba oil. • Neem Oil: Effective as both an insecticide and fungicide.
4 - Chemical Control Methods
• Fungicides, such as sulfur and potassium bicarbonate, can effectively control the disease. • Sulfur-based Fungicides: Safer Garden Fungicide (wettable sulfur). • Copper-based Fungicides: Available but not highly effective against powdery mildew. • However, it is important to follow label instructions carefully and avoid overuse of chemicals to prevent harmful effects on the environment and non-target organisms.
