Begonia plants, encompassing over 1,000 species, are prized for their lovely leaves and flowers. Browning of begonia leaves indicates a problem with the plant.
A disease called powdery mildew results in begonia leaves eventually turning brown if heavily infected. Powdery mildew is manifested initially by small white spots appearing on the leaves. This disease is treated by removal of infected leaves and using proper fungicide as soon as the spots appear.
Leaf Spot Diseases
Leaf spot diseases, such as gloeosporium and cladosporium, cause brown and tan spots to appear on begonia leaves. The spots range in size and amount. These diseases are treated by removing infected leaves or using specific fungicides.
Botrytis blight is a fungal disease that results in brown spots appearing on begonia leaves. Some leaves have so many spots that the leaf appears to turn brown in color. Removing infected leaves and using proper fungicides will treat the begonia plant.