Crown galls (Agrobacterium tumefaciens) are fungi that affect ficus plants, causing swollen, cork-like areas on the leaves that could look crusty. Prune off infected areas and destroy. If the crusty area is black, it is the fungus sooty mold. Usually aphids are present with an outbreak of sooty mold. Treat the aphids with insecticide and wash the mold from the plant's leaves.
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Joyce Starr is a freelance writer from Florida and owns a landscaping company and garden center. She has published articles about camping in Florida, lawncare, gardening and writes for a local gardening newsletter. She shares her love and knowledge of the outdoors and nature through her writing.