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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

• Crown Gall

Viral

• Rose Mosaic
• Rose Rosette

Fungal​

• Black Spot
• Cankers
• Powdery Mildew​​

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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

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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 Illinios Extenstion, 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, Powdery Mildew

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Viral

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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:   

• K-State Extension, Rose Mosaic Virus  PDF
• New Mexico State U., Rose Mosaic Virus  PDF

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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:  K-State Extension, Rose Rosette  PDF