Marin Rose Society

FAST FACTS - BLACK SPOT
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 or systemics such as Funginex

Dormant spray with horticultural oil and copper or lime sulfate after pruning

Elimination:

Spray with baking soda and horticultural oil, Banner Maxx, Benlate, Compass, Daconil 2787, Fungi-gard, Funginex, Fore or Sentinal

GOOD GUY / BAD GUY?

A really bad guy—one of the most common diseases of roses

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