Zucchini Powdery Mildew: Identification and Milk Spray Treatment

Confirming Powdery Mildew

White spots on zucchini leaves after rainy, warm weather are classic powdery mildew—a fungal disease (Podosphaera xanthii). It thrives in humidity with moderate temps, not soaking rain.

Eco-Friendly Treatment: Milk Spray

Milk is an effective, non-toxic fungicide for mildew:

• Mix 1 part milk to 9 parts water (or up to 40% milk).
• Spray tops and undersides of leaves weekly.
• Reapply after rain.
• Safe for edibles, no residue concerns.

Other Organic Options

• Potassium bicarbonate (similar to baking soda but more effective).
• Neem oil or horticultural oil.
• Sulfur dust (avoid in heat >85°F).

Cultural Prevention

• Space plants for air flow.
• Water at base—avoid wetting leaves.
• Remove severely infected leaves.
• Rotate cucurbits yearly.

Mulch Note

Grass clippings can mat and hold moisture—fluff or replace with straw to improve air movement at soil level.