How long can Phytophthora ramorum survive in soil moved from an infested area?

Survival of P. ramorum (SOD pathogen) in dead hosts or non-plant substrates is extremely variable and strongly affected by climatic factors. Although a comprehensive study on this topic has not conducted, extrapolating from several studies we can say the following:

Soil becomes more infectious from late winter to early summer in the presence of rainfall, so any movement of soil away from a SOD-infested area from January to July could transport viable P. ramorum.

Keep the following in mind:

  • The larger the volume of soil moved, the greater the risk.
  • In organic rich soils (e.g. top layers of forest soils), pathogen survival is less than 18 months.
  • If P. ramorum is present in green waste incorporated in the soil, survival can be much longer (2 years or more).
  • In inert soils (e.g. potting mix), the pathogen can survive multiple years.  However, for all soils, areas with less temperate climates (cold winters, hot summers) may hasten loss of pathogen viability.

From a practical perspective, if infested forest soil is picked up on tires or shoes from late winter to early summer, the pathogen will likely remain viable for about 1 year, in the absence of incorporated green waste. If soil is picked up from late summer to early fall, survival duration is much less, possibly in the order of a few months.

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