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

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