The Norwegian Scientific Committee for Food Safety (VKM) has at the request of the Norwegian Food Safety Authority assessed the effect of a risk reduction option of fire blight corresponding to the EU minimum requirements, on the spread of the disease in Norway and the potential for on crop loss.
The reason for the request is that the Norwegian Ministry of Agriculture and Food has asked the Norwegian Food Safety Authority to make a cost - benefit evaluation of management strategies for the two plant diseases, fire blight and apple proliferation phytoplasma (witches' broom).
Fire blight is a serious plant disease caused by the bacterium Erwinia amylovora. The disease causes rapid wilting of flowers and shoots of susceptible ornamental shrubs in the rose family and fruit trees of apple and pear.
Fire blight is now widespread in North and Central America, Asia and New Zealand. The disease has spread in Europe over the past 50 years.
The fire blight bacterium was first found in Norway in 1986. Since then the disease has gradually spread northward along the west coast to Ålesund, and southward to Søgne. The main hosts in Norway have always been the ornamental shrubs Cotoneaster bullatus and C. salicifolius.
After 27 years in Norway, the disease is still confined to the outer coastal areas, and has so far not occurred in any areas of commercial fruit growing.
EU’s minimum requirements
Management of fire blight in accordance with the EU minimum requirements means no governmental supervision and no actions taken at an outbreak of fire blight in orchards, parks, and private gardens. It will also bring about a significant relief to the import restrictions that are currently in place in Norway.
As for nurseries, the governmental supervision will be only in nurseries producing host plants for fire blight.
If fire blight is detected in a nursery, infested plants will be destroyed. Sales will be prohibited until both destruction and follow-up inspection after two and four weeks are completed.
Read about the Norwegian Food Safety Authority's emergency plan for fire blight (in Norwegian) on their website.
The spread of fire blight
With a management in accordance with the EU minimum requirements, the number of fire blight outbreaks will probably increase over a five year period.
This is particularly true if import of plants with a low phytosanitary status is allowed.
In the long term (30 years), one can expect extensive damage. It is also likely that outbreaks of fire blight could become present in all regions of the country where host plants are cultivated.
VKM estimate that the uncertainty in this assessment is low.
Consequences for commercial fruit production
Fire blight has so far not been detected in Norwegian fruit production. There are therefore no Norwegian reports on crop losses caused by fire blight outbreaks on commercial fruit production,
Warm and humid weather is favorable for the fire blight bacterium. Fruit trees are especially susceptible to infection via flowers. Under current climate conditions, the flowering period of fruit trees in Norway is short due to the synchronizing effect of the cold winter.
The flowering period occurs in early spring and generally ends before the weather becomes warm and conducive for infection by the fire blight bacterium.
VKM is therefore of the opinion that the frequency of fire blight attacks in commercial fruit production will be limited under the current climate conditions, perhaps in line with the extent of damage caused by the fungal diseases scab and fruit tree canker.
The risk of infection may increase under climate change and elevated temperature in particular, both because the weather conditions will become more favorable for the fire blight bacterium and because of altered phenology due to extension of the vulnerable flowering period that may for overlap more frequently with periods of warm and humid weather. However, it is uncertain how much the risk of infection will increase.
Under current cultivation practices the distance between trees are shorter and the rows are narrower when planting new orchards, than in the past.
Such cultivation practices leads to more humid local environment and thus more favorable conditions for the fire blight bacterium. Shorter distances between the trees will aid more rapid spread of the disease from one tree to another.
Consequences for nurseries, parks, private gardens, etc.
If implementing the EU minimum requirements for domestic management of fire blight in Norway, the corresponding management action to be taken against a disease outbreak is estimated to have low efficacy. VKM concludes that the damage by an outbreak might be significant.
The Panel on Plant Health in the VKM is responsible for this assessment.