Downy Mildew in Hardy Geranium
Hardy geraniums (cranesbills) are ground-covering perennials with deeply lobed leaves and abundant flowers in blue, pink, or white from late spring through summer. A water mould disease causing yellowing on upper leaf surfaces with greyish-purple fuzzy growth underneath — distinct from powdery mildew which grows on top of leaves.
Hardy Geranium care requirements
These care conditions are most relevant to downy mildew in Hardy Geranium. Check each one as a potential cause.
Symptoms to look for in Hardy Geranium
- fiber_manual_recordYellow, pale green, or brown patches on upper leaf surfaces
- fiber_manual_recordGreyish, purple, or white fuzzy growth on the underside of leaves
- fiber_manual_recordLeaves wilting and dying in wet conditions
- fiber_manual_recordRapid spread through a crop in cool, wet weather
Common causes in Hardy Geranium
- fiber_manual_recordDamp conditions with temperatures between 10–15°C
- fiber_manual_recordHigh humidity and poor air circulation
- fiber_manual_recordOverhead watering and rain splash spreading spores
- fiber_manual_recordInfected seedlings or plant material
How to diagnose downy mildew in Hardy Geranium
The fuzzy growth on the undersides of leaves is the key identifier. Unlike powdery mildew, downy mildew prefers cool, wet conditions and does not rub off easily.
How to treat downy mildew in Hardy Geranium
Remove and destroy affected leaves and plants. Apply a copper-based fungicide. Improve ventilation and reduce humidity. Avoid overhead watering. There is no cure once severely infected — remove affected plants to prevent spread.
Preventing downy mildew in Hardy Geranium
Space plants adequately. Water at the base. Improve greenhouse ventilation. Choose resistant varieties. Rotate crops annually to prevent build-up of spores in soil.