Angel wing begonias are also known as cane begonias. The angel wing begonia is grown more for its large, attractive leaves than for its pretty pink or red flowers. When purchasing an angel wing begonia (most are sold in small pots), check the entire plant for pests and signs of disease. Many pests like to feed off the underside of the leaves. Most diseases can be found on the leaves or in the root system of the plant.
Xanthomonas Leaf Spot
Xanthomonas leaf spot is a common bacterium found on angel wing begonias. Water the plant from below to keep the foliage dry and help prevent this disease. Xanthomonas leaf spot appears as speckling on the leaves. Infected plants should be discarded and not used for cuttings or in compost. Using slightly higher than normal amounts of fertilizer can help prevent the disease.
Botrytis blight first appears on the lower leaves of the angel wing begonia. The affected leaves are usually touching the soil. The blight starts off as water spots on the leaves, which then turn dark brown to black. Botrytis blight tends to be a problem in areas with cool nights and warm day temperatures, combined with high moisture. Control botrytis blight by keeping the leaves dry or, if the disease does not clear up on its own, using fungicide.
Pythium Root Rot
Pythium root rot affects plants that have a poor root system. Eventually, the root rot turns the leaves yellow. Root rot first appears on stems near the soil, turning them black and mushy. Root rot spreads easily to other cuttings. Reduce watering to the absolute minimum to prevent root rot, and make sure your potting soil is sterilized. Plants with root rot should be discarded and not composted.