- 3.8.1 Probability of entry
- 3.8.2 Probability of spread
- 3.8.3 Economic consequences
- 3.8.4 Overall assessment of risk
3.8 Nectria galligena
3.8.1 Probability of entry
In assessing the risk of entry of this disease, the most important factor is that expression of the disease will only occur where rainfall is greater than 1000mm (Dubin and English, 1975). Production areas such as Hawkes Bay, Blenheim, Canterbury and Central Otago are therefore very likely to be free of this disease. If fruit was sourced from these areas, the risk of the disease entering Australia as a latent infection on the fruit is negligible. In addition, most of Australia does not have the rainfall required for the disease to establish.
In areas with greater than 1000mm rainfall, Nectria galligena fruit infection only occurs where the disease is present in or close to the orchard. The disease can only travel 10 meters under normal conditions or 125m under storm conditions and infection is not spread by insects. If a tree was found to be infected in a fruit producing orchard, the tree is likely to be removed to prevent further infection.
Nectria galligena will only occur in exported fruit as a latent infection. If infection occurs before harvest, the fruit will develop lesions and will not be exported. If a late season infection of the fruit occurs the fruit can develop latent infections and these infections may survive the storage period. Little information is available on how long infections will remain latent in storage or the effect of storage temperature on latent infections. Fruit with latent infections become more susceptible to rotting as storage time increases, such latent infections are likely to be detected at phytosanitary or on-arrival inspection.
AFFA suggests that most nursery stock in New Zealand comes from areas where the disease is prevalent (i.e., Waikato) and this would mean that newly established orchards were a source of inoculum, raising the probability of fruit infection. However, if the nursery stock is planted to regions with less than 1000mm rainfall (as in the regions previously mentioned) the disease will not be expressed and there is no danger of fruit infection.
If N. galligena were present on imported fruit as a latent infection causing a rot, it is important to consider the mechanism or vectors for transfer of the disease to a host. The principal means indicated in the data sheet is rain runoff and rain splash, both of which are short distance means of dispersal. The likelihood of a host being close to an infected fruit is very low.
| New Zealand believes that the probability of entry of N. galligena on fruit from areas with rainfall above 1000mm is very low and negligible from areas with rainfall below 1000mm. |
3.8.2 Probability of spread
The risk of spread has been assessed by AFFA as 'high' (likely to occur), but the evidence given does not support this. The disease will generally only spread 10m by conidial dispersal and transfer between orchards in this manner is unlikely. Long distance spread of the disease is more likely to occur with transfer of planting material, however this would be limited if proper sanitation was practised, and interstate movement controls were exercised. Nectria galligena has been in New Zealand but not under official control for many years. In a survey undertaken last season (1999/00) of the South Island and the Hawkes Bay, the disease was only recorded on one tree from Nelson.
| New Zealand considers that the probability of spread in areas with rainfall below 1000mm is negligible and very low in areas with higher rainfall. |
3.8.3 Economic consequences
The disease did establish in Tasmania but was eradicated, proving that if established, it could be controlled/eradicated. It is likely that establishment of the disease would be recognised at a national level the impact will be restricted to a single geographic region where rainfall is greater than 1000mm. This is equivalent to a moderate economic impact not a high impact as suggested by AFFA.
| New Zealand believes that the economic consequences of this pest are moderate. |
3.8.4 Overall assessment of risk
| AFFA has assessed the overall risk of N. galligena as low. New Zealand believes that this is an over-estimate of risk on the basis of a moderate economic impact and a very low risk of entry. |
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