Information, including identification, symptoms and control, related to most common diseases that plague rose growers in Western Missouri and Eastern Kansas. 
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Cleanliness is the best method of reducing problems that can arise once roses are established. Always remove prunings, leaf litter and faded flowers; use clean mulch; keep beds free of weeds; and, of utmost importance, use clean pruning equipment to reduce transmission of disease.
Select Below to Learn More About​
Bacterial

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Crown Gall
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Description:
  • Infection of a wide variety of plants caused by Agrobacterium tumefaciens.
  • Bacteria enter roots, stems, or branches through wounds.

Symptoms:
  • Irregular tumor like growths on stems and roots.
  • Initially light colored and smooth; hard, dry, cracked, and dark color with age.
  • Usually on main stem at soil line.
  • May form below soil line.

Control:
  • Prevention by planting infection free plants.
  • Infected plants should be removed along with surrounding soil and placed in the trash.
  • Do not compost infected plants after removal.
  • Sterilized pruning tools after use on infected plants.
                  
Reference: U. of Minnesota, Crown Gall

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Fungal
Black Spot
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Description:  
  • Fungal infection of rose bushes that occurs in wet weather or leaves are damp from overhead sprinklers or frequent watering.
  • Spores are splashed up onto the rose leaves from the soil.

Symptoms:
  • Infection is first noticed when blackspots appear on the leaves.
  • The leaves turn yellow and eventually fall off.
  • Blackspot can cause total defoliation.

Control:
  • Use a routine spray program to reduce or prevent blackspot.
  • Application frequency depends on the severity of the infection and the effectiveness of the spraying program.

Prevention:
  • Planting resistant varieties of roses.
  • Plant far enough apart to allow good airflow between plants.
  • Prune the plants to keep the center open.
  • Pick up all infected leaves that fall from the plants.
  • Remove infected leaves from the plants if the infection is wide spread.
  • Remove leaf litter from the area.

Reference: K-State Extension, Rose Black Spot  PDF

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Cankers

Description:
  • Caused by several different parasitic fungi entering the stem through wounds or dying tissue.
  • Appear as small lesions on the woody tissue of canes.
  • Result in poor growth of the affected area and eventual death of the cane.
 
Symptoms:
  • Brand canker appears as black sooty patches that develop during winter on climbing roses and those covered for winter protection. Cracking bark is common.
  • Brown canker appears as light brown lesions with deep purple margins.
  • This fungus will also attack foliage and buds on some cultivars.
  • Stem canker appears as black spots, often at the point of mechanical damage. It is some what reddish and becomes brown, sunken and cracked with age.

Control:
  • Maintain a preventive fungicide spray program to control diseases.
  • If cankers appear,  prune the cane well below the canker with clean pruning shears.
 
Reference: U. of Maryland Extension, Rose Cankers

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Powdery Mildew

Description:
  • Caused by a fungus.
  • Occurs during early summer and early autumn
  • Humid days (64 to 75°F) coupled with cool nights (50 to 55°F) enhance germination of powdery mildew spores.
  • Prolonged rainy periods are not favorable for spore germination.
         
Symptoms:
  • Appears as a whitish-gray, powdery coating at the tips of canes.
  • Young leaves often become dulled, distorted and dwarfed.
  • With severe infections, tip dieback can occur.
 
Control:
  • Remove leaf debris from garden.
  • Fungicidal sprays may be necessary to control sever infection.            
Reference: Texas A & M Agrilife Extension, Powdery Mildew

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Viral
Rose Mosaic
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​Description:
  • Caused by prune necrotic ringspot virus and apple mosaic virus.
  • Viruses found worldwide.

Symptoms:
  • Usually appear in spring and are variable.
  • Appears as chlorotic bands or ring spots, wavy lines, yellow vein banding, yellow splotches on green leaves.
  • Leads to decreased vigor, fewer flowers, lower transplant survival, and higher winter-kill.

Control:
  • No cure for infection, so remove and destroy plant.
  • Prevented by using virus free buds and root stock for vegetative propagation of roses.       
 
Reference:   

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Rose Rosette
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Description:
  • Widely spread in the Midwest after first being discovered in the United States about 75 years ago. 
  • Wild roses and cultivated roses are susceptible
  • Caused by a negative-sense RNA virus
  • Virus needs living tissue for replication.
  • Carried by a microscopic mite, Phyllocoptes fructiphilus.  
  • Mite is blown in on the wind or moves from plant to plant attached to insects.
  • Mites transfer the virus to the rose bush while feeding. 
  • Affected plants will eventually die from the RRD virus infection.
Symptoms:
  • Elongated, reddish new growth that stays red.  It is not unusual to see reddish new growth, but normal growth typically turns green as it matures. 
  • Excessive prickles, usually smaller than normal, appear on the canes. 
  • Leaves are chlorotic, deformed, narrow, and/or small. 
  • Flower buds don’t open normally.
  • Blooms are deformed. 
  • New, infected canes are larger than the cane from which they arise. 
  • Multiple branches on the end of canes form the characteristic ‘witches broom’ growth. 
  • Many of these changes mimic herbicide damage, so a detailed history and careful examination of surrounding plants is necessary to eliminate herbicide drift as a cause of unusual growth among roses.
         
Control:
  • No effective treatment for RRD virus infected roses. 
  • Infected plants should be removed and discarded in the trash, as soon as, RRD is diagnosed. 
  • New or replacement roses can be planted in the same spot after waiting a week. 
 
Reference: