Roses are susceptible to a range of diseases outdoors. The following table summarizes key diseases, symptoms, pathogens, and management strategies.
| Disease | Symptoms | Pathogen/Cause | Management |
|---|---|---|---|
| Anthracnose | Dark purple to black spots with narrow dull-brown border; centers turn gray and fall out. Similar spots on canes. | Sphaceloma rosarum | Maintain sanitation. Black spot control procedures also control anthracnose. |
| Black Spot | Brown to black round spots with feathery edges on leaves; leaves yellow and fall. Small purplish spots on canes. | Diplocarpon rosae | Remove infected canes and fallen leaves. Keep foliage dry. Apply fungicide to protect new growth. |
| Botrytis Blight | Small water-soaked lesions on petals; gray fungal growth. Stubs after harvest become infected, fungus moves down to girdle cane. | Botrytis cinerea | Space plants for air circulation. Remove fading flowers and yellowing leaves. Apply fungicide to protect healthy tissue. |
| Cankers | Reddish-brown spots on canes turn light to dark brown, covered with tiny black dots (fruiting structures). Cankers girdle and kill canes. | Coniothyrium fuckelii, Cryptosporella umbrina, Coniothyrium wernsdorffiae, Cylindrocladium scoparium | Do not plant stock with cankers. Remove infected canes, cutting above a bud. Apply fungicide after pruning. Disinfect shears between cuts. Maintain even soil moisture and moderate fertilization. |
| Crown Gall | Small white to cream galls on stems enlarge to 6 inches. Can form on roots or stems. | Agrobacterium tumefaciens | Do not plant infected material. Apply Agrobacterium radiobacter at transplant to protect healthy plants. |
| Downy Mildew | Purplish-brown spots on leaves during cool, damp spring; leaves yellow and fall. Small spots or long purplish areas on twigs. | Peronospora sparsa | Keep leaf surfaces dry. Apply fungicide. |
| Powdery Mildew | Spots on leaves, stems, flower parts expand and become covered with white fungal growth. Small dead spots on some cultivars. | Sphaerotheca pannosa | Apply fungicide. |
| Rose Rosette | Distorted leaves, often bright red. Excessively thorny canes, slow maturation. Witches'-broom branching. | Rose rosette virus vectored by eriophyid mites. | Destroy infected plants. Eliminate multiflora roses within 100 ft. |
| Rust | Orange powdery spores on lower leaves and canes in spring/summer; black spores in autumn. | Phragmidium spp. | Immediately destroy infected plants (not common in U.S., serious threat). Bury or bag and landfill. Only roses susceptible; fungus dies without host. |
| Viruses | Mosaic, mottling, yellow line or ring patterns; vein yellowing. Includes rose mosaic, mottle, yellow mosaic, ring pattern, streak, tobacco streak, rose rosette, rose wilt, spring dwarf, color break, strawberry latent ring spot. | Various viruses. | Destroy infected plants. Plant only healthy, virus-free stock. Maintain insect and mite control. |
Images: Rose black spot on leaves and cane; Anthracnose; Downy mildew; Powdery mildew on leaf and flower stem; Virus symptoms; Canker symptoms and fruiting structures; Rust; Crown gall.
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