Geranium maderense · Biennial
Powdery mildew: Improve air circulation and apply a suitable fungicide if infection is severe.
Downy mildew: Avoid wetting foliage when watering and remove affected leaves promptly.
Root rot: Ensure well-drained compost and allow the surface to dry out between waterings.
Vine weevil: Apply a systemic insecticide drench or use biological nematodes in the soil.
Slugs and snails: Use slug pellets, beer traps, or copper tape barriers to deter feeding.