Begonia annulata
Root rot: Water only when the top soil is dry and ensure pots have adequate drainage holes.
Powdery mildew: Improve air circulation around the plant and treat with a suitable fungicide if severe.
Spider mites: Increase humidity around the plant and spray affected areas with water or use horticultural oil.
Aphids: Wipe off by hand or spray with a strong jet of water; use insecticidal soap if infestation persists.
Leaf drop: Avoid sudden changes in temperature or humidity and ensure consistent, moderate watering.