Pest Risk Analysis (PRA) Stage Pest Risk Analysis (PRA) Stage 2: Pest Risk Assessment2: Pest Risk Assessment

Overall Assessment of RiskOverall Assessment of Risk

Outline

• Part of the pest risk assessment process• Qualitative descriptions - free text• Qualitative descriptions – word scales• Group discussion• Summarising aspects of risk assessment• Combining likelihood and impact

– Summarising the summary!

Stages

• Stage 1: Initiation• Stage 2: Pest Risk Assessment

– Step 1: Pest Categorization– Step 2: Assessment of the Probability of

Introduction and Spread– Step 3: Impacts– Step 4: Overall Assessment of Risk– Step 5: Uncertainty

• Stage 3: Pest Risk Management

Overall assessment of risk• Combines the likelihood of pest

introduction with the consequences of that introduction

• “Without any mitigation measures, the pest is likely to be present on (host) from (origin) and to be able to survive transport and reach suitable hosts such as …. which are widely distributed in the PRA area”

Overall assessment of risk• Combines the likelihood of pest

introduction with the consequences of that introduction

• “Without any mitigation measures, the pest is likely to be present on (host) from (origin) and to be able to survive transport and reach suitable hosts such as …. which are widely distributed in the PRA area and could cause yield losses of up to 15% during a severe outbreak”

Overall assessment of risk• “Although the pest can spread (be

introduced – enter and establish) from neighbouring country ….. impacts are likely to be very low”

• Improvement

Overall assessment of risk• “Although the pest can spread (be

introduced – enter and establish) from neighbouring country ….. impacts are likely to be very low”

• Improvement

• “Although the pest is very likely to spread (be introduced – enter and establish) from neighbouring country ….. impacts are likely be very low”

Overall assessment of risk• Summarise using words

– Advantages

– Disadvantages

• Alternative approach?

Summarising aspects of PRA• Word scale

• Likelihood– Very unlikely

– Unlikely

– Likely

– Very likely

Summarising aspects of PRA• Word scale

• Impact– Negligible

– Low

– Medium

– High

Guidelines for rating establishment

• Negligible • The pest has no potential to survive and

become established in the PRA area.– Stewart’s wilt of corn (Erwinia stewartii (Smith)

Dye) distribution is limited by the overwintering capabilities of its insect vector, the corn flea beetle (Chaetocnema pulicaria Melsheimer). In most years, winter temperatures throughout Canada’s corn-growing regions are too low to allow survival of the insect-vector, in which the bacterium could overwinter.

Guidelines for rating establishment

• Low• The pest has potential to survive and

become established in approximately one third or less of the range of the host(s) in the PRA area. – Oriental fruit moth (Grapholita molesta

(Busck)) distribution in Ontario is primary limited to the south, whereas its hosts are widely distributed in the province.

Guidelines for rating establishment

• Medium• The pest has potential to survive and become

established in approximately one third to two thirds of the range of the host(s) in the PRA area. – Example: Blueberry Maggot (Rhageletis mendax

Curran) distribution is limited by low winter temperatures to the more southerly portions of the range of Vaccinium species in Canada. It will not survive throughout the entire range of blueberry.

Guidelines for rating establishment

• High• The pest has the potential to survive and

become established throughout most or all of the range of hosts in PRA area. – Example: Current Old World distribution of Cherry

Ermine Moth (Yponomeuta padellus (L.)) suggests that the pest could become established in North America wherever its hosts are found.

Summary for rating establishment

• Negligible = no potential

• Low = 1/3 or less of host range

• Medium = 1/3 to 2/3 of host range

• High = most or all of host range

Guidelines for rating introduction

• Negligible • The likelihood of introduction is extremely low

given the combination of factors including the distribution of the pest at source, management practices applied, low commodity volume, low probability of pest survival in transit, low probability of contact with susceptible hosts in the PRA area given the intended use, or unsuitable climate.

Guidelines for rating introduction

• Low

• The likelihood of introduction is low but clearly possible given the expected combination of factors necessary for introduction described before

Guidelines for rating introduction

• Medium

• Pest introduction is likely given the combination of factors necessary for introduction described before

Guidelines for rating introduction

• High

• Pest introduction is very likely or certain given the combination of factors necessary for introduction described before

Guidelines for rating introduction

• Negligible = extremely low

• Low = low

• Medium = likely

• High = very likely or certain

Guidelines for rating impact

• Negligible• There is no impact on yield, host

longevity, production costs or storage.– Example: Septoria leaf spot (Septoria ampelina

Berk. and Curtis) infection results in leaf drop in grape that is premature by a few days only, with no treatment necessary and no economic losses.

Guidelines for rating impact

• Low• The pest has a minor impact on the

standing crop and little effect on the stored products. – Example 1: Apple Rough Skin agent is

responsible for loss of marketability of fresh fruit and is most significant on the apple varieties Golden Delicious, Belle de Boskoop, Schonen van Boskoop and Glorie van Holland.

Guidelines for rating impact

• Medium

• The pest has a moderate impact on the standing crop but host mortality is rare; losses in storage may occur.– Example: Apple maggot (Rhagoletis

pomonella (Walsh)) is a fruit borer. Losses may be up to 75% of fruit if left untreated.

Guidelines for rating impact

• High• The pest has a severe impact on the

standing crop with significant host mortality; losses in storage may be total.– Example: All species of oak are susceptible to

Oak wilt (Ceratocystis fagacearum (Bretz) Hunt), although less severe symptoms are demonstrated by those in the white oak group. Red oaks are usually killed within a few weeks to one year of initial infection.

Risk matrixHigh

Medium

Low

Negligible

Negligible

Low Medium High

Likelihood of introduction

Imp

act

Risk matrixHigh

Medium

Low

Negligible

Negligible

Low Medium High

Likelihood of introduction

Imp

act

Summary

• Part of the pest risk assessment process

• Qualitative descriptions - free text• Qualitative descriptions – word scales• Summarising aspects of risk

assessment• Combining likelihood and impact

– Summarising the summary!