Marin Rose Society

FAST FACTS - RUST
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 or systemics such as Funginex

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, Banner Maxx, Benlate, Funginex, Fore or Immunox

GOOD GUY / BAD GUY?

Definitely a bad guy—one of the most common diseases of roses

Return to the Main Page