Rose Diseases (Outdoors)
Gary W. Moorman, Professor of Plant Pathology
|Anthracnose||Dark-purple to black spots are bordered by a narrow, dull-brown band. Centers of spots turn gray and fall out. Spots similar to leaf spots form on canes.||Sphaceloma rosarum||Maintain good sanitation. Black spot control procedures (below) also control anthracnose.|
|Black spot||Brown to black round spots with feathery edges form on leaves. Leaves yellow and fall. Small, purplish spots form on canes.||Diplocarpon rosae||Remove infected canes. Remove and destroy fallen leaves. Water in a manner that keeps foliage surfaces dry. Apply a fungicide to protect new foliage.|
|Botrytis blight||Small, water-soaked lesions form on petals. Gray fungal growth covers infected petals. Stubs left after harvest become infected. The fungus then moves down to girdle the cane.||Botrytis cinerea||Space plants to ensure good air circulation. Remove fading flowers and yellowing leaves. Apply a fungicide protect healthy tissue.|
|Cankers||Reddish-brown spots on canes turn light to dark brown and become covered with tiny, black dots (fungal fruiting structures). Cankers girdle and kill the cane.||Coniothyrium, fuckelii, Cryptosporella umbrina, Coniothyrium wernsdorffiae, Cylindrocladium scoparium||Do not plant stock with cankers. Remove infected canes, making the cut immediately above a bud. Apply a fungicide after pruning. Sterilize the shears with a disinfestant between cuts. Maintain even soil moisture and moderate fertilization.|
|Crown gall||Small white to cream-colored galls that form on stems may enlarge to 6 inches in diameter. Galls can form on roots or stems.||Agrobacterium tumefaciens||Do not plant infected material. Apply Agrobacterium radiobacter to protect healthy plants at transplant.|
|Downy mildew||Purplish-brown spots form on leaves during cool, damp spring weather. Leaves yellow and fall. Small spots or long, purplish areas may form on and kill twigs.||Peronospora sparsa||Water in a manner that keeps leaf surfaces dry. Apply a fungicide.|
|Powdery mildew||Spots on leaves, stems, and flower parts expand and become covered with white fungal growth. Small dead spots form on some cultivars.||Sphaerotheca pannosa||Apply a fungicide .|
|Rose Rosette||Leaves are distorted and often bright red. Canes are excessively thorny and mature very slowly. Plants may branch excessively (witches’-broom).||Rose rosette virus vectored by eriophyid mites.||Destroy infected plants. Eliminate multiflora roses in a 100’ radius of desired roses.|
|Rust||Lower leaves and cane tissue in the spring and summer have masses of orange powdery spores. Black spores form on the leaves and other parts in autumn.||Phragmidium||Infected plants should be immediately destroyed since this disease is not common in the U.S. and poses a serious threat to roses. Bury infected plant material or seal in a plastic bag and send it to a landfill. Only roses are susceptible. The fungus will die quickly if no roses are available for infection.|
|Viruses||Leaves may exhibit mosaic, mottling, yellow line, or ring patterns. Veins may turn yellow.||Rose mosaic, mottle, yellow mosaic, ring pattern, or streak virus. Tobacco streak. Rose rosette, rose wilt, spring dwarf, or color break virus. Strawberry latent ring spot.||Destroy infected plants. Plant only healthy, virus-free plants. Maintain good insect and mite control.|
Rose black spot on leaves and cane.
Powdery mildew on leave and flower stem.
Canker symptoms and fruiting structures.
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