Phytophthora cactorum

Plant Damange:

Foliar leaf spots, shoot blight, root and crown rot.

Multiple Hosts:

  • Crabapple (Malus)
  • Dogwood (Cornus)
  • Rhododendron (Rhododendron)
  • Madrone (Arbutus)
  • Spruce (Picea)


The disease is found in nurseries with poor drainage. In addition, foliar disease of Rhododendron is found during wet conditions caused by excessive overhead irrigation during the warm season.


Root infection occurs in spring when soils are at or near saturation and zoospores move toward the root. The disease progresses up into the root crown area, often forming a bleeding canker. Infection can also occur directly through pruning wounds. Leaf and shoot infection occurs when infested water is splashed or applied to the plant canopy.


This pathogen survives as spores in the soil, organic debris, container media, or infected tissue.