Why is my Edgeworthia covered in a white, powdery substance?

If your Edgeworthia is covered in a white, powdery substance, it is likely suffering from powdery mildew. Powdery mildew is a fungal disease that is common in humid or damp conditions. It typically appears as a white or gray powder on the leaves, stems, and flowers of plants. To treat powdery mildew, remove any affected plant parts and increase air circulation around the plant. You can also apply a fungicide to prevent the disease from spreading.