Powdery Mildew and Downy Mildew — How to Distinguish and Treat
Pe scurt: White coating on leaves isn't necessarily the same problem. Powdery mildew and downy mildew look similar but have different causes and different treatments — confusing them costs you the whole season.
Mildew — Two Different Problems, Two Different Solutions
White fluffy coating on leaves. They look similar, but these are two completely different pathogens requiring completely different approaches.
Powdery Mildew (Erysiphe):
- White powdery coating ONLY on the upper surface of leaves
- Can be easily rubbed off with your finger
- Appears in dry air and large temperature fluctuations
- Attacks: cucumbers, pumpkins, zucchini, onions, grapes
Downy Mildew (Peronospora):
- Yellow or olive spots on top of the leaf
- Gray or purple fluffy coating ON THE UNDERSIDE of the leaf
- Appears in humid air and cool nights
- Attacks: cucumbers, lettuce, onions, spinach
Treating Powdery Mildew:
- Milk diluted 1:9 with water — spray the leaves. It works!
- Baking soda (1 teaspoon per liter of water + a few drops of dish soap)
- Diluted garden lime — preventively
Treating Downy Mildew:
- Remove diseased leaves, don't compost them
- Copper-based preparations (Miedzian) — approved for organic cultivation
- Improve ventilation and avoid wet leaves
Preventing both: Ventilation, watering at the roots, avoiding excess nitrogen.
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