by Nanette Londeree, Master Rosarian
SYMPTOMS
- Powdery pustules of light orange to yellow spores on under sides of leaves in early spring
- Red brown to orange spores on under sides of leaves in summer, turning black in fall
- Upper sides of leaves may discolor and leaves may drop
- Can affect leaves, succulent canes and flower parts
CAUSE
- Infection by the fungus Phragmidium disciflorum
- Airborne spores infect leaf tissue
OPTIMAL CONDITIONS
- A common diseases of roses and other plants
- Prevalent during damp or rainy weather
- Temperatures of 65–70°F with 2 – 3 hours of free water 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
- 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:
- Prune back severely affected canes
- Spray with baking soda and horticultural oil
- For more details about disease management visit the UC IPM website
GOOD GUY / BAD GUY?
Definitely a bad guy—one of the most common diseases of roses