by Nanette Londeree, Master Rosarian
SYMPTOMS
- Characteristic round black spots on upper surface of leaves or stems
- Spots have feathery or fiber like margins; no powdery growth on the underside of leaves
- May be yellowing around the spots that extend to the entire leaf
- Small black fruiting bodies may be present in spots on upper sides of leaves
- Spots are generally seen first on leaves close to the ground
- Infected leaves may drop off; the entire plant may be defoliated
- Miniature roses are generally more susceptible
CAUSE
- Infection by the fungus Diplocarpon rosae
- Airborne spores infect leaf tissue
OPTIMAL CONDITIONS
- One of the most common diseases of roses and other plants
- Prevalent during rainy weather
- Temperatures of 65 – 75°F and at least 7 hours with free water on leaves for germination
- Fungus can overwinter as dormant mycelium or resting spores on infected stems and leaves
TREATMENT
Prevention:
- Buy and plant disease-free plants
- Choose resistant varieties; glossy foliaged varieties generally have better resistance to most fungal diseases
- Plant roses in areas with good soil drainage and ventilation; avoid shady spots and dense plantings
- Avoid wounding plants during transplanting
- Maintain good garden sanitation; remove and destroy infected leaves and canes during the season
- Avoid overhead watering if time / temperature is insufficient to dry leaves within a few hours
- Spray with baking soda and horticultural oil, anti-transpirants, botanicals such as Neem oil
- Dormant spray with horticultural oil and copper or lime sulfate after pruning
Elimination:
Spray with baking soda and horticultural oil; for additional details on management visit the UC IPM website.
GOOD GUY / BAD GUY?
A really bad guy—one of the most common diseases of roses