nurtomiPowdery mildew
A white powdery coating may be a fungal growth.
What to look for
Look for patches on leaves, shoots or buds that spread over time. Powdery mildew is different from cotton-like insects and mineral residue; appearance varies by plant and other problems can look similar.
What to do
Remove badly affected leaves when practical and give the plant space for gentle airflow. Keep checking new growth. If it spreads, consult guidance for the particular plant before choosing a labeled treatment.