Angel wing (Begonia coccinea) produces large, attractive leaves and grows outdoors as a specimen plant in U.S. Department of Agriculture plant hardiness zones 10a through 11a and as an indoor container plant everywhere else. Angel wing begonias can reach up to 35 to 48 inches tall, have evergreen leaves and bunches of red or cerise flowers. When grown indoors, begonias are virtually disease-free, but outdoors, disease and pests can cause black spots on the plant's leaves.
Xanthomonas leaf spot (Xanthomonas campestris) commonly affects angel wing begonias. The disease firs appears as speckling on the leaves and leads to necrotic spots and leaf drop. You can introduce this bacteria inadvertently by bringing infected plants into the garden or greenhouse and through improper sanitation. Prevent this by inspecting plants before buying, removing and destroying infected plants and, in greenhouses, not crowding plants and avoiding high humidity and wet foliage.
Two types of fungi commonly affect angel wing begonias and cause black spots on leaves. Botrytis blight (Botrytis cinerea) appears first on the lower plant leaves and on leaves touching the soil. The fungus starts off as water spots that eventually turn necrotic and dark brown to black. Botrytis blight is problematic in areas with cool nights and warm days with high humidity or moisture. Proper sanitation, inspection of plants and removing diseased plant parts help manage the disease.
Myrothecium leaf spot (Myrothecium roridum) causes black spots on leaves. The leaves appear water-soaked at first and then turn brown to black in color. Like botrytis blight, the spots appear as necrotic areas on lower leaves and often occur as a result of too much moisture and poor greenhouse sanitation.
Insects that can cause black spots on angel wing begonia leaves include shoreflies and whiteflies. Shoreflies are tiny black flies that sit on leaf tips, feeding on algae. These pests do not cause damage by feeding on leaves; they spread disease and reduce plant value by defecating on leaves, leaving small black or green spots. Whiteflies leave small yellow spots where they feed, but they also secrete honeydew that can encourage sooty mold.
Disease and Insect Prevention
The best way to prevent disease and insect problems is to inspect plants before bringing them home. At the first sign of disease, prune plants to removed infected plant parts and sanitize tools. Discard any pruning debris or heavily infected plants. To remove insects, try washing plants with soapy water and soft cloth or brush. You may also use a fungicide or pesticide.
- National Gardening Association: Begonia Coccinea
- Clemson Cooperative Extension: Growing Begonias Indoors
- University of Florida MREC: Begonia Production Guide
- University of California Agrictulture & Natural Resources: Floriculture and Ornamental Nurseries Begonia (Begonia Spp.)
- Michigan State University Extension: Bacterial Leaf Spot of Begonia
- Cornell University Cooperative Extension of Schenectady County: Botrytis Blight
- Heritage Fungicide: Ornamental Diseases: Myrothecium Leaf Spot
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