Rose Diseases (Outdoors)
Gary W. Moorman, Professor of Plant Pathology
| Disease | Symptoms | Pathogen/Cause | Management |
|---|---|---|---|
| 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 one of the following to protect new foliage: chlorothalonil, mancozeb, thiophanate methyl, thiophanate methyl + mancozeb, azoxystrobin, neem oil, myclobutanil, triforine or ziram. Triadimefon can stunt some cultivars. |
| 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 chlorothalonil, fludioxonil, or iprodione to 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 (see black spot) 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 mancozeb, azoxystrobin, potassium salts of phosphorus acid, or mancozeb + thiophanate methyl. |
| 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 azoxystrobin, myclobutanil, potassium bicarbonate, kresoxim methyl, chlorothalonil, triflumizole, piperalin, fenarimol, sulfur, triadimefon, triforine, or ziram. Triadimefon can stunt many cultivars. |
| 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.
Anthracnose.
Downy mildew.
Powdery mildew on leave and flower stem.
Virus symptoms.
Canker symptoms and fruiting structures.
Rust.
Crown gall.
Active Ingredients and Trade Names of the Chemicals
| FRAC Group No. | Risk Level | Class | Active ingredient | REI Restricted Entry Interval | Trade names (EPA reg. No.) |
|---|---|---|---|---|---|
| 1 | 3 | Benzimidazole | thiophanate methyl | 12 | 3336 (1001-69), OHP 6672 (51036-329-59807), Fungo Flo (51036-329-59807), Systec 1998 (48234-12) |
| 2 | 3 | Dicarboximide | iprodione | 12 | Chipco 26GT (100-1138), Chipco 26019 (264-481), Iprodione (51036-361), Sextant (51036-361-59807) |
| 3 | 2 | Pyrimidine | fenarimol | 12 | |
| Piperazine | triforine | 12 | |||
| Triazole | triadimefon | 12 | |||
| myclobutanil | 24 | Systhane (707-253) | |||
| 5 | Piperidine | piperalin | 24 | Pipron (67690-1) | |
| 11 | 3 | Strobilurin | azoxystrobin | 4 | Heritage (10182-408) |
| 12 | 2 | Phenylpyrol | fludioxonil | 12 | Medallion (100-769) |
| 40 | Cinnamic acid | ||||
| derivative | dimethomorph | 12 | Stature (241-419-67690) | ||
| M | 1 | Chloronitrile | chlorothalonil | 48 | Daconil (50534-9) |
| 12 | Echo (60063-7), PathGuard (60063-7-499), Concorde (72167-24-1812), Pegasus (72167-24-1812) | ||||
| Dithiocarbamate | mancozeb | 24 | Dithane (707-180), FORE (707-87), Pentathlon (1818-251) | ||
| manganese + zinc | 24 | Protect T/O (1001-65) | |||
| ziram | 48 | Ziram (4581-140) | |||
| U | 1 | Phosphite | phosphorus acid salts | 4 | Alude (71962-1-1001) |
| potassium phosphate | 4 | Vital (42519-24) | |||
| NC | 1 | potassium bicarbonate | 4 | Armicarb (5905-541-AA), Milstop (70870-1-68539), Kaligreen (70231-1), Remedy (62719-70), Agricure (70870-1-1001) | |
| neem oil | 4 | Trilogy (70051-2), Triact (70051-2-59807) | |||
| sulfur | 24 | Kumulus (51036-352) | |||
| Combined products | 1 | ||||
| 1 + M | thiophanate methyl + mancozeb | Zyban (58185-31) |
Fungicides and Fungicide Resistance Management - Certain fungicides, usually systemic fungicides, are said to be 'at risk' to the development of resistance if they are used repeatedly. See the Risk Level in the above table (1 = low risk; 3 = high risk). The Fungicide Resistance Action Committee has developed a numbering system in which chemicals with the same FRAC Group number have the same mode of action (See http://www.frac.info/frac/index.htm ). It is recommended that chemicals at high risk be used sparingly and in rotation or mixed with chemicals with different modes of actions (different FRAC number).
Canker symptoms and fruiting structures.
| Biological control agent (type of organism) | Trade Name (EPA Reg. No) | Target Pathogen |
|---|---|---|
| Agrobacterium radiobacter (bacterium) | Galltrol A (strain 84) (40230-1) Norbac 84C (strain K84) (38087-2) | Agrobacterium tumefacians (crown gall) |
DISCLAIMER
Notice: The user of this information assumes all risks for personal injury or property damage.
Warning! Pesticides are poisonous. Read and follow all directions and safety precautions on labels. Handle carefully and store in original labeled containers out of the reach of children, pets, and livestock. Dispose of empty containers right away, in a safe manner and place. Do not contaminate forage, streams or ponds.
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