IPM of Rose Diseases

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IPM OF ROSE DISEASES by Baldo Villegas
Environmental Research Scientist/Entomologist
Orangevale, California
E-Mail: sactorose@yahoo.com
Home Page: http://www.sactorose.org/

Pest/Pathogen

Favorable Conditions

Chemical Control Measures

Non-chemical Control Measures

Powdery Mildew (Fungus) -- the white growth of the fungus consists of mycelium and conidiophores and appears as patches on leaves and stems. Young tissue is most susceptible. This is an obligate parasite.

Night temperature of 15.5E C [60E F] and relative humidity of 90-99%; Day temperature of 26.7E C [80E F] and 40-70% RH.

Note: Warm season disease; does not require free moisture for spore germination.

1. Apply a dormant spray during the winter months.

2. Spray with available protectant or systemic fungicides.

3. Some antitranspirants have shown fungicidal activity by acting as a barrier to invading spores.

1. Acquire resistant varieties of roses

2. Remove infected plant material as soon as it is noticed and get rid of plant materials after pruning; practice winter sanitation.

3. Avoid overcrowding rose plants and choose open beds away from fences and wind obstructions.

4. Open the center of the plants when you prune to provide air circulation through the leaf canopy.

Black Spot (Fungus) -- characteristic black spots develop on the upper leaf surfaces. Leaf spots are usually circular with characteristic fringed borders. Raised purple-red, irregular blotches may develop on young canes of susceptible varieties.

The fungal spores (conidia) must be immersed in water and must be continuously wet for at least seven hours for any infection to occur.

Note: Spring and fall disease in most of CA; needs free moisture.

Same as above.

1. Follow above recommendations for powdery mildew.

2. Avoid overhead irrigation/sprinklers.

3. Water early in day to allow leaves to dry.

4. Leaves should not be allowed to remain wet or at very high humidity for more than 7-12 hours.

Rust (Fungus) -- the powdery pustules of orange to orange-red spores (aeciospores or uredospores) on the undersides of the leaves in mid spring through fall are very diagnostic. Black pustules containing teliospores may be present during the winter months. This fungus is an obligate parasite.

The optimal conditions for disease development are temperatures of 18-21E C [64-70 EF] and continuous moisture for two to four hours.

Note: Spring and fall disease in most of CA; needs free moisture.

Same as above.

1. Follow recommendations for black spot, and avoid wetness of the leaves or high humidity around the foliage for longer than two hours.

2. Pick off some of the lower leaves near the ground from the rose bushes, but avoid sun burning the bud-union of the rose bush.

Spot Anthracnose (Fungus) -- Circular spots are scattered or grouped, sometimes coalescing into one another; spots are reddish to purplish on upper surface of leaf; In order spots the center are whitish in color an margin is dark red/purplish.

Humid, cool conditions are ideal for this fungus.

Same as above

Follow above recommendations for rust and blackspot.

Downy Mildew (Fungus) -- This fungus is characterized by purplish to black areas on leaves, stems, and peduncles. This is followed by yellowing of the leaflets and complete defoliation of the plant. The fungal mycelia are intercellular in rose tissue. This fungus is an obligate parasite.

Humid, cool conditions are ideal for this fungus.

Note: Early spring and late fall disease; rarely if ever seen in CA during the summer; needs free moisture.

 

Same as above. In the past fungicides like Zyban7 or Duosan7 and others containing chlorothalonil like Daconil 27877 have been used for controlling this fungus.

Follow above recommendations for rust and blackspot.

Common Canker (Fungus) -- Wounds are necessary for infection. Canker begins as small yellow to red spots in the bark and gradually expands. The centers of the cankers become light brown and the margin a darker brown.

Cold moist weather conditions

1. Apply dormant sprays after winter pruning.

2. Apply fungicidal sprays to cover wounds.

1. Practice sanitation by removing infected parts of canes on plants and by removing infected debris from the rose garden after winter pruning.

2. Seal pruning wounds.

3. Sterilize tools whenever they become in contact with infected parts of the plant.

4. Avoid injury to rose canes; use sharp tools to obtain clean cuts.

5. Pruning cuts should be made above bud-eyes and at an angle.

Botrytis Blight (Fungus) -- the grayish brown mycelial growth is very characteristic of this fungus. It is a pest of stored/refrigerated roses, rose buds (that can't open), cut flowers, rose plants, and cuttings used for propagation.

Also on canes as a secondary low-level pathogen on tissue or flower petals.

Cool temperatures, high humidity, and moisture.

Note: Early season and late fall disease; needs free moisture.

Same as above.

1. Follow above recommendations for rust.

2. Biological control methods are being looked at but they are not available commercially.

Crown Gall (Bacterium) -- gall formations on the crown, roots, and even twigs are characteristic of this bacterial disease. Aerial galls may be found on tree roses.

Naturally present in most soils. Bacterial pathogen enters plant through wounds, either natural or caused by pruning, grafting, or mechanical injury by tools.

Note: Bacteria persistent in soil for long time. Moving soil or transplanting can easily move spores to other places.

Use biological antagonists (e.g., Gallex7, Galltrol7, etc.). a) Gallex7 is a ready-to-use emulsion that can be applied directly with a brush. b) Galltrol7 is a culture of live bacteria. It is applied as a dip or spray on seeds, cuttings, and bareroot plants.

1. Resistant varieties.

2. Exclusion -- keep it out of your garden.

3. Sanitation -- clean up/dispose of infected plants; sterilize tools if contaminated between pruning.

4. Refuse to purchase plants with galls.

Rose Mosaic (Virus) -- visible symptoms are variable but include chlorotic line patterns, ring spots, and mottling of leaves and some flower break. No adverse effect on flower production has been reported, but foliar symptoms detract from the overall quality.

Virus transmission in roses appears to be limited to vegetative propagation when virus infected buds, scions, or rootstocks are grafted to healthy plants. However, Prunus Necrotic Ringspot Virus (PNRS) and Apple Mosaic Virus (APMOV) may be pollen transmitted.

No chemical controls are currently available.

1. Resistant varieties, if any.

2. Exclusion of infected plants from rose garden, but difficult, especially when one gets bareroot roses.

3. To be on the safe side, sterilize cutting tools when pruning infected plants.

4. Graft or propagate only healthy plants.

5. Let your nursery dealer know you will not purchase roses from anyone selling infected plants.

NOTE: When symptoms are recognized in obligate parasites (e.g., Powdery Mildew, Rust, and Downy Mildew) it is best to use a systemic fungicide, which may have some eradicant properties.

 

 

 

 BLACK SPOT

RUST

DOWNY MILDEW

SPOT ANTHRACNOSE

POWDERY MILDEW

Characteristic black spots develop on the upper leaf surfaces. Leaf spots are usually circular with characteristic fringed borders. Raised purple-red, irregular blotches may develop on young canes of susceptible varieties.

The powdery pustules of orange to orange-red spores (aeciospores / uredospores) on the undersides of the leaves in mid spring through fall are very diagnostic. Black pustules containing teliospores may be present during the winter months. This fungus is an obligate parasite.

This fungus is characterized by purplish to black areas on leaves, stems, and peduncles. This is followed by yellowing of the leaflets and complete defoliation of the plant. The fungal mycelia are intercellular in rose tissue. This fungus is an obligate parasite.

This fungus is characterized by purplish to black areas on leaves, stems, and peduncles. This is followed by yellowing of the leaflets and complete defoliation of the plant. The fungal mycelia are intercellular in rose tissue. This fungus is an obligate parasite.

The white growth of the fungus consists of mycelium and conidiophores and appears as patches on leaves and stems. Young tissue is most susceptible. This is an obligate parasite.



If you have any questions or constructive comments, I would love to hear from you, please send e-mail to Baldo Villegas



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Last updated: July 28, 2003