WSU Extension

Hortsense

Common Diseases
 
Armillaria root rot 
Botrytis blight (Gray mold) 
Cankers 
Crown gall 
Damping-off 
Dead roots 
Dodder 
Downy mildew 
Dwarf mistletoe 
Galls 
Leaf spots and blights 
Nectria cankers 
Phytophthora root rot 
Powdery mildew 
Pseudomonas bacterial canker 
Root rots 
Rusts 
Sclerotinia white mold 
Sudden oak death 
Tubercularia canker 
Verticillium wilt 
Viruses 



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Caption: Hypericum rust
Photo by: R.S. Byther
  
Common Diseases : Rusts
(revision date: 4/30/2013)


Biology
In general, rust diseases are easily diagnosed because of the abundant production of colorful powdery spores formed in tiny pustules. Microscopic examination may be necessary to identify specific rust pathogens. Spore production sometimes is limited to the underside of leaves, while the top surface may show discolored spots. Fruit infections may occur in susceptible fruiting plants. Many rust spores appear orange to yellow, while some rusts produce brown to black spores. Most rusts are very host specific and only infect certain plants. Many rusts also need two different types of plants (primary and alternate hosts) to complete their life cycle.
Management Options

Non-Chemical Management
  • Rake up and destroy all dead leaves.
  • Plant resistant cultivars.
  • Removing infected leaves early in the season may be effective in some home gardens.
  • When applicable, remove alternate hosts growing in the near vicinity.
  • Prune out and destroy infected and dead wood during the dormant season.
Select non-chemical management options as your first choice!

Chemical Management

Certain fungicides are effective in protecting plants from infection. Refer to the specific host for registered pesticide effective in managing rusts.

Images

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Caption: Hypericum rust
Photo by: R.S. Byther
Caption: Rust on serviceberry
Photo by: R.S. Byther
Caption: Fuchsia rust
Photo by: R.S. Byther
Caption: Fuchsia rust: close-up of fruiting bodies
Photo by: R.S. Byther
Caption: Geranium rust: upper leaf surface and lower leaf surface
Photo by: R.S. Byther
Caption: Geranium rust: close-up of sporulation
Photo by: R.S. Byther
Caption: Oregon grape rust
Photo by: R.S. Byther
Caption: Oregon grape rust
Photo by: R.S. Byther
Caption: Hollyhock rust
Photo by: R.S. Byther
Caption: Amelanchier rust
Photo by: R.S. Byther
Caption: Snapdragon rust
Photo by: R.S. Byther