Powdery Mildew

by Nanette Londeree, Master Rosarian

SYMPTOMS

  • White, gray or silver talcum-powder-like growth on the tops of leaves, primarily new growth
  • May appear on stems, buds or sepals
  • First observed on new growth and distorts or curls the edges of leaves; leaves may be permanently twisted
  • Growing tips and buds may look badly deformed or be killed
  • When the disease is severe, plants become stunted and leaves curl and drop
  • Mature leaves are generally not infected

CAUSE

  • Infection by the fungus Sphaerotheca pannos var rosae
  • Airborne spores infect tender new growth

OPTIMAL CONDITIONS

  • Most prevalent in spring and fallTemperatures 60 – 80°F, with 40 – 70% relative humidity during the day, and up to 95% at night
  • Does not need free water to reproduce
  • 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
  • Water leaves daily (overhead) in the morning
  • 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, Bayleton/Strike, Erase, Fungi-gard, Immunox, Rally or Rubigan

GOOD GUY / BAD GUY?

Definitely a Bad Guy. One of the most common diseases of roses and other plants

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