White Powder on Shrub: Powdery Mildew Identification and Treatment

The white, brush-off powder on your shrub in Israel's arid/semi-tropical climate is almost certainly powdery mildew, a fungal disease that thrives in dry, warm conditions with high humidity around leaves.

Why It's a Problem

Mildew coats leaves, blocking photosynthesis, weakening the plant, and making it susceptible to other stresses.

Organic Treatment Options

1. Milk Spray: Mix 1 part milk to 9 parts water; spray weekly, covering both leaf surfaces. Changes leaf pH, inhibiting fungus.
2. Potassium Bicarbonate: More effective than baking soda. Mix 1 tablespoon per gallon water + 1 tsp horticultural oil or soap. Spray weekly.
3. Neem Oil: Fungicidal and insecticidal; follow label rates.
4. Improve Airflow: Prune surrounding plants to reduce humidity.
5. Water at Base: Avoid wetting foliage.

Prevention

• Choose mildew-resistant varieties.
• Space plants for good air circulation.
• Apply preventive sprays early in season if mildew is recurrent.

Since the gardener wasn't concerned, the infestation may be light. Start with milk or potassium bicarbonate sprays and monitor.