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How to Manage Pests

UC Pest Management Guidelines


Harvested roses.

Floriculture and Ornamental Nurseries

Rose (Rosa spp.)

Disease Control Outlines

(Reviewed 3/09, updated 3/09)

In this Guideline:


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.

[Precautions]

PUBLICATION

[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Floriculture and Ornamental Nurseries
UC ANR Publication 3392
Diseases
S. T. Koike, UC Cooperative Extension Monterey County
C. A. Wilen, UC IPM Program, UC Cooperative Extension San Diego County
Acknowledgment for contributions to Diseases:
R. D. Raabe, (emeritus) Environmental Science, Policy, and Management (ESPM), UC Berkeley
A. H. McCain, (emeritus) Environmental Science, Policy, and Management (ESPM), UC Berkeley
M. E. Grebus, Plant Pathology, UC Riverside

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