DIY Fungicide: Baking Soda & Horticultural Oil Formula for Powdery Mildew

The Proven Recipe

Mix in 1 gallon of water:

• 4 teaspoons baking soda (≈1 rounded tablespoon)
• 1 tablespoon horticultural oil (or citrus oil + 1 tsp molasses)

Spray lightly on foliage affected by powdery mildew, black spot, brown patch, or other fungal diseases. Apply early morning or evening—avoid hot sun. Repeat weekly and after rain.

Why It Works

• Baking soda: Raises leaf surface pH, inhibiting fungal spore germination.
• Horticultural oil: Smothers existing spores and helps solution adhere.
• Potassium bicarbonate can substitute for baking soda (less sodium buildup in soil).

Critical Cautions

1. Don’t overuse: Excess sodium harms soil biology. Limit to 1–2 applications per month.
2. Never drench soil: Spray foliage only. Soil accumulation damages roots.
3. Test first: Spray a few leaves, wait 48 hours. No burn = safe to proceed.
4. Not a cure: Prevents spread; doesn’t reverse existing damage. Remove severely infected leaves first.

For Your South Georgia Crape Myrtles

• Start spraying at first sign of white powdery coating (usually late spring).
• Improve air circulation: prune crowded branches.
• Avoid overhead watering—use drip irrigation.
• Choose resistant varieties for new plantings: ‘Natchez’, ‘Muskogee’, ‘Tuscarora’.

This homemade remedy is a staple for organic gardeners. Used correctly, it keeps mildew manageable without harsh chemicals.