| Disease (causal agent) |
Symptoms |
Survival of pathogen and effect of environment |
Comments on control |
Armillaria root rot
(Armillaria mellea) |
A general decline and eventual
death. White plaques of fungal growth develop between bark and wood. |
In infected wood buried in soil.
Could be introduced with leaf mold if there are woody branches or roots present or in incipient infection on plant. |
Fumigate infested soil with methyl bromide/chloropicrin combination. |
Black spot
(Diplocarpon rosae) |
Black
spots with
fringed margins mainly on both sides of leaves and on succulent stems.
Yellowed areas develop around spots. Causes defoliation. |
On living and dead leaves, and on infected stems. Waterborne spores are spread by splashing water. |
Avoid wetting foliage. Remove,
incorporate, or burn infected fallen leaves when pruning. Protect foliage with chlorothalonil. Do not compost unless using rapid methods. |
Botrytis blight
(Botrytis cinerea) |
Spotting of flower petals and bud rot. Twig dieback and cane canker. Woolly gray fungal spores form on decayed tissues. |
Plant debris. Favored by high humidity, condensed moisture, and low temperatures. Spores are airborne. |
Clean up debris. Protect susceptible tissues with chlorothalonil, iprodione, mancozeb. |
Canker diseases
(Coniothyrium fuckelli, Botryosphaeria
dothidea, Cryptosporella
umbrina) |
Brown cankers, sometimes with gray
centers. Small, black, spore‑producing fungal structures (pycnidia) develop in dead tissues. |
On dead plants and debris. Favored
by wet weather. Spores are waterborne. Infection occurs mainly through wounds. |
Keep plants in vigorous condition. Prune diseased portions. When pruning, cut back to node. |
Crown gall
(Agrobacterim tumefaciens) |
Overgrowths or galls form on stem and roots. Infection occurs mainly through wounds. |
In soil. Bacteria spread in water. Gall development is favored by rapidly growing host. |
Avoid injuring base of plant and
roots. Paint galls with Gallex to eradicate them. Use good sanitation in
propagating areas. more info * |
Downy mildew
(Peronospora sparsa) |
Purplish red to dark brown,
irregular angular spots on leaves. Lower surface covered with sparse, downy fungal growth that may be hard to see. Leaves turn yellow and fall. |
Spores produced only on living
plants. Resistant spores (oospores) carry fungus over unfavorable periods. Moist, humid conditions. |
Protect foliage with mancozeb,
fosetyl-al, or mefenoxam. more info * |
Powdery mildew
(Sphaerotheca pannosa var. rosae) |
White‑to‑gray powdery growth on leaves and other green parts, mainly on new
growth. Leaves are distorted and discolored. |
On living plants and in infected
buds. Favored by moderate temperatures (60° to 80°F) and high relative humidity at night (90 to 99%). |
Protect foliage with fenarimol,
myclobutanil, neem oil, propiconazole, stylet oil, potassium bicarbonate, or
sulfur. Eradicate infections with horticultural oils, neem oil, or jojoba oil.* |
Rust
(Phragmidium disciflorum or
P. speciosum, P. mucronatum) |
Small orange
pustules on
undersides of leaves and other green parts. Leaves frequently are yellow. May
cause defoliation. Cultivars differ widely in susceptibility. In fall, black teliospores form on leaves. |
On living leaves; rarely on stems.
Favored by cool, moist weather, and condensed water on leaves. Spores are airborne. |
Avoid overhead irrigation. Protect
foliage with myclobutanil, triadimefon, or mancozeb. Remove and destroy all
leaves during winter months. more info * |
Verticillium wilt
(Verticillium dahliae) |
Leaf fall is followed by dieback of one or more shoots. One‑sided purpling of stems sometimes present. |
In soil for many years. May go
undetected in budwood. Symptoms are most severe during warm weather following a cool period. |
Fumigate infested soil. Obtain
disease‑free plants. Manetti rootstock is resistant to most strains of
the fungus. more info * |
| |
| Virus or viruslike disease |
Symptoms |
Host range and natural spread |
Comments on control |
Mosaic
(Prunus necrotic ringspot virus) |
Symptoms vary with rose cultivar
and virus. Symptoms range from general yellowing to conspicuous
yellow blotches and intricate rings with line patterns. Plants may be somewhat stunted. |
Carried in living plants and
spread by budding and grafting and by rooting cuttings from infected plants.
No insect vectors known. Symptoms appear at moderate-to-low temperatures and are masked at high temperatures. |
Obtain virus-free plants. Heat
treatment helps control the virus in rose stocks; 100°F temperatures for 4 weeks inactivates virus in 99% of cuttings taken from treated plants. |
Rose leaf curl
(probably a virus) |
Downward curling of leaves and
cane dieback. Leaves readily fall from new shoots, which are characteristically pointed with a broad base. |
Infected rose plants. Slow natural spread. |
Obtain virus-free plants. Destroy infected plants. |
Rose ring pattern
(probably a virus) |
Symptomless or inconspicuous in
some cultivars, especially floribunda types. Rosa multiflora 'Burr' is severely stunted with small, deformed leaflets that have a
distinct mottling and wrinkling. Most hybrid teas show green mosaic and fine‑line patterns in few or many leaves. |
Infected rose plants. No natural spread. Readily transmitted by grafting. |
Obtain virus-free plants. Virus is sensitive to thermal inactivation. (See Mosaic.) |
Rose spring dwarf
(probably a virus) |
Leaves that emerge in spring are
balled or recurved on very short shoots and exhibit conspicuous vein clearing. Symptoms tend to disappear later in growing season. |
Infected rose plants. No natural spread. |
Obtain virus‑free plants. |
| Roses are
also susceptible to crown canker (Cylindrocladium scoparium), gray mold * (Botrytis cinerea),
hairy root (Agrobacterium rhizogenes), root lesion nematode ** (Pratylenchus spp.), root knot nematode** (Meloidogyne spp.), and virus diseases: leaf curl (virus suspected), Rosette (virus suspected), and streak (virus suspected). |
| * For additional information, see section on Key Diseases. |
| ** For additional information, see section on Nematodes. |
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