Module 3: Phytophthora ramorum
Module 2: Disease Management
Welcome Module 1: Biology, symptoms, and Diagnosis Conclusion Take the Exam Further Information

What is Phytophthora?

Life Cycle

Disease Cycle

Seasonal Activity

Virtual Dying Plant


Practice Questions 



Stem canker on flowering pear from rain-splashed infection Phytophthora syringae.

Photo by R. Regan.

Foliar blight on Kalmia caused by phytoplithone syringae.

Foliar blight on Kalmia caused by Phytophthora syringae.

Photo by N. Grunwald.

Plant Damange:
Foliar leaf spots, shoot blight, and stem cankers.

Foliar leaf spot on Rhododendron.

Photo by R. Linderman.

Multiple Hosts:

  • Ash (Fraxinus)
  • Crabapple (Malus)
  • Flowering pear (Pyrus)
  • Mountain laurel (Kalmia)
  • Lilac (Syringae)
  • Rhododendron (Rhododendron)

This disease is found wherever bare-root trees are grown, although development is favored by cool and misty conditions, such as foggy areas along waterways. Rhododendrons grown in containers and fields are also susceptible.

Stem canker on crabapple
following winter infection with Phytophthora syringae.

Photo by R. Regan.

Rain splash from infested standing water spreads the pathogen. Plant tissue wounded by harvest or pruning is at increased risk of disease.

This pathogen survives as spores in soil and in fallen leaves; spores become active during prolonged periods of standing water.

<< Previous Next >>

Oregon State University Extended Campus
4943 The Valley Library, Corvallis, OR 97331-4504
800-667-1465 | 541-737-9204
Contact us with your comments and questions
Copyright 2008 Oregon State University