How to Detect and Prevent Powdery Mildew

Powdery mildew attacks flowering annuals. This fungus thrives with heavy rainfall and high humidity, but is also caused by temperature changes between day and night. Foliage suffering from powdery mildew looks like it has a white coating of talcum powder.

Difficulty:

Moderate

Instructions

Things You'll Need

• Spray Bottles
• Garden Hoses
• Gardening Gloves
• Horticultural Oils
• Leaf Rakes
• Shovels
• Baking Soda
• Sulfur Powder

1. Look for a grayish-white powder on leaves. Plants affected by this disease include roses, zinnia, zucchini and verbena.

2. Avoid overhead irrigation if possible. If there are sprinklers near the affected plants, either cap them or move the plants to a drier location.

3. Water in the early morning hours so that plants have a chance to dry during the day. When watering plants, avoid wetting leaves. Hold the hose near the base of the plant instead of watering from overhead.

4. Protect plants from heavy rainfall. Place susceptible plants under overhangs or eaves.

5. Clean your garden of any infected plants, especially in winter, for maximum protection against the disease. Dispose of infested plants and don't compost them.

6. Keep the area under mildew-prone plants raked and clean. Fungus spores splash back onto the foliage during rainfall or irrigation.

7. Spray with a solution of 1 tsp. baking soda and 1/2 tsp. horticultural oil mixed with 1 qt. of warm water in a 1-qt. sprayer. Don't forget to spray the undersides of leaves.

8. Spray or dust plants with sulfur-based fungicides as a last resort.

Tips & Warnings

• Plant mildew-resistant varieties of plants. Waxy-leaved plants, including bird of paradise, canna and aspidistra, are usually resistant to powdery mildew.

• Although powdery mildew looks horrible, it causes little harm to the plant. Harvest your zucchini and enjoy the fruits of your labor.

• Always use the least toxic method of control as your first step.

• Fungicides are among the most toxic garden chemicals. Wear goggles, neoprene gloves, a respirator, and long sleeves and pants when applying them.