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Pest Risk Assessment Summary

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The likelihood of introduction of Phytophthora ramorum to Canada is considered to be high (numerical score 3), based on factors including the volume and source of material that is potentially infected or infested, and the availability of susceptible hosts at ports of entry. Climate-based predictive maps all indicate that south-coastal B.C. is highly suitable for the establishment of P. ramorum. There is considerable disagreement in terms of the suitability of other areas with some models suggesting no risk to eastern Canada while others predict that areas in south central B.C., southern Ontario, Nova Scotia, P.E.I., New Brunswick and southern Newfoundland are at low to moderate risk.

The consequences of introduction are estimated to be medium (numerical score 2) for the most suitable areas (south-coastal British Columbia), low (numerical score 1) for warmer areas of southern Ontario, Quebec, inland B.C. and the Maritime provinces and negligible for other areas of Canada. Although establishment potential is highest on the west coast, there is a considerable resource that could be at risk in eastern Canada, though there are a number of factors that could mitigate this risk. The potential direct economic losses that could occur in Canada due to the introduction of P. ramorum are negligible when considering the entire PRA area (all of Canada), medium in south-coastal B.C., low in the warmer areas of Ontario, Quebec and the Maritimes as well as the rest of B.C., and negligible in the rest of the country. Should the survival, persistence, spread and damage potentials of the pathogen prove to be much higher than is currently indicated by information pertaining to the known infested areas of California, Oregon, and Europe, these ratings would need revision.

Overall risk rating:

The overall risk rating for P. ramorum is medium for south-coastal British Columbia and low for warmer areas of southern Ontario, Quebec, inland B.C. and the Maritime provinces. Other areas of Canada have an overall risk rating of negligible, reflecting the ratings applied individually to both likelihood and consequences of introduction.

As demonstrated by ongoing survey results, the measures taken to inspect for and detect P. ramorum appear incapable of preventing a low rate of national and international movement of the pathogen in nursery stock. This is due in part to the inevitable reliance upon visual inspection to screen massive volumes of material prior to subjecting it to costly testing procedures. Resources for laboratory testing probably remain the principal constraint on all surveillance systems. Nursery certification measures in both the United States and the European Union have resulted in a downward trend in the number of positive plants detected but this could be as a result of improved pest management procedures on the part of producers.

As long as planting material continues to move intra- and intercontinentally in huge volumes there is virtually no way to absolutely prevent the movement of this and many other serious pathogens around the globe.

Level of uncertainty: medium - low

Understandably, the overall level of uncertainty assigned to the first assessment of P. ramorum in 2001 was rated as high. Over time, subsequent revisions have reflected a growing knowledge of the pathogen and levels of uncertainty have been justifiably reduced to medium - low.

In what amounts to an almost unprecedented response by the scientific community to characterize a new invasive plant pest, an excellent understanding of the P. ramorum has been rapidly developed. In only a few years, sizable research budgets have stimulated significant leaps in understanding this pathogen and, incidentally, many other congeneric species, several of which are new to science. Levels of uncertainty will continue to drop, albeit more slowly, supported by the burgeoning platform of scientific literature and expertise. However, due to the complexity of biotic systems, an absolute understanding of all issues is elusive and it is thus unrealistic to rate overall uncertainty as low, primarily when one considers the remaining gaps in information, especially those that would be unique to, or have particular relevance to, Canada. However as each year passes the epidemiological facts on the ground are giving scientists greater confidence that the risks from P. ramorum are understood.

A copy of the full Pest Risk Assessment is available by contacting the Plant Health Risk Assessment Unit.

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