Phytophthora syringae

Plant Damange:

Foliar leaf spots, shoot blight, and stem cankers.

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.


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.