WSU Extension


Bacterial soft rot and blackleg 
Late blight 
Potato leafroll mosaic (Leafroll) 
Powdery scab 
Rhizoctonia canker (Black scurf) 
Scab (Common) 
Verticillium wilt (Potato early dying) 
Colorado potato beetle 
Potato flea beetles 

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Caption: Potato soft rot
Photo by: R.S. Byther
Potato : Bacterial soft rot and blackleg
(revision date: 6/3/2014)

Soft rot and blackleg are both caused by bacteria. The soft rot symptoms typically appear on tubers. The small to large circular lesions are sunken, tan or brown, water-soaked areas on the tuber surface. The affected internal tissues are white to tan and develop a soft, almost odorless rot. An amber liquid may ooze from rotting areas. Blackleg symptoms are generally limited to leaves and stems. Leaves curl upward and turn yellow. Soft, light brown to black lesions develop at the base of stems and may spread into a black, slimy rot of tubers. In dry weather, the stem discoloration may be internal only, but under favorable conditions for disease development (warm, moist weather), plants wilt and die. The bacteria are carried in contaminated plant debris, water, soil, and seed pieces and are easily spread by splashing water, insects, and equipment.
Management Options

Non-Chemical Management
  • Plant disease-free seed, using uncut seed potatoes when possible. Do not plant seed pieces which have lesions.
  • Rotate crops. Do not plant potatoes in the same location each year.
  • Plant in well-drained soil.
  • Avoid injury to plants and tubers. Injuries provide potential infection sites.
  • Remove and destroy infected plants and tubers when noticed.
  • Remove plant debris from the garden. Destroy or discard (do not compost) diseased materials.
  • Harvest mature potatoes during dry weather, taking care to prevent injuries. Allow tubers to dry before storing.
Select non-chemical management options as your first choice!

Chemical Management

None recommended


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Caption: Potato soft rot
Photo by: R.S. Byther
Caption: Potato soft rot
Photo by: R.S. Byther
Caption: Potato blackleg symptoms
Photo by: R.S. Byther
Caption: Potato blackleg symptoms
Photo by: R.S. Byther