WSU Extension

Hortsense

Rose
 
Disease
Black mold 
Black spot 
Botrytis bud and twig blight 
Brand canker 
Bullheading (cold damage) 
Common canker 
Crown gall 
Downy mildew 
Powdery mildew 
Rust 
Viruses 
Insect
Leafcutting bees 
Leafrollers 
Redhumped caterpillar 
Root weevils 
Rose aphids 
Rose galls 
Rose leafhopper 
Rose midge 
Roseslug 
Spider mites 
Thrips 
Tobacco budworm 
Western spotted cucumber beetle 



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Caption: Downy mildew on rose
Photo by: R.S. Byther
  
Rose : Downy mildew
(revision date: 4/11/2018)


Biology
Downy mildew can affect leaves, stems, flower stems, and flower parts. The infection is usually found only on young growth. On leaves, symptoms include purplish or brown spots, usually between veins, and yellow leaves with green spots. Infected leaves may drop off the plant. Grayish fungal masses may be found on the underside of some infected leaves (unlike powdery mildew, which is white and found on both sides of leaves). Symptoms on stems and flower parts can include small or large purple to black spots. Small infected twigs can be killed.
Management Options


Non-Chemical Management
  • Plant varieties that are less susceptible to the disease.
  • Collect and destroy all fallen leaves from beneath plants.
  • Prune and destroy all infected portions of plants.
  • Space plantings and prune to provide good air circulation.
  • Avoid overhead watering to help reduce humidity around plants.
Select non-chemical management options as your first choice!

Chemical Management

Focus on cultural control. Copper fungicides may have some efficacy, but may cause discoloration of foliage or blooms.

Listed below are examples of pesticides that are legal in Washington. Always read and follow all label directions.
  • Agri-Fos Systemic Fungicide
    Active ingredient: mono- and di-potassium salts of phosphorous acid  |  EPA reg no: 71962-1-54705
  • Bonide Copper Fungicide Spray or Dust RTU [Organic]
    Active ingredient: basic copper sulfate  |  EPA reg no: 4-58
  • Bonide Fruit Tree & Plant Guard Conc
    Active ingredient: boscalid, lambda-cyhalothrin, pyraclostrobin  |  EPA reg no: 4-488
  • Bonide Fruit Tree & Plant Guard R-T-Spray
    Active ingredient: boscalid, lambda-cyhalothrin, pyraclostrobin  |  EPA reg no: 4-488
  • Soap-Shield Flowable Liquid Copper Fungicide [Organic]
    Active ingredient: copper octanoate  |  EPA reg no: 67702-2-56872
  • This list may not include all products registered for this use.
Images

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Caption: Downy mildew on rose
Photo by: R.S. Byther