Pest risk assessment of Phytophthora fragariae in Norway

These are two of the conclusions in a risk assessment of the red core disease of strawberry plants made by the Norwegian Scientific Committee for Food Safety (VKM). The risk assessment was commissioned by the Norwegian Food Safety Authority (Mattilsynet).

Difficult to eradicate

The red core disease of strawberry plants is caused by the oomycete Phytohthora fragariae Hickman. The oomycete infects the roots of the strawberry plants and reduces growth and crop yield. The pathogen is spread mainly by strawberry plants, but also by other pathways like water or soil.

When the disease is present it is difficult to get rid of, because P. fragariae can survive in soil without host plants for a long period of time (at least 12 years).

P. fragariae is a quarantine pest forbidden to introduce and spread in Norway. It is present in certain areas in Norway. In order to limit introduction and spread of the pathogen, import of strawberry plants is prohibited, plants to be traded must be tested and found to be free from the pathogen, and places of production where the pathogen has been detected are under strict regulations.

VKM has assessed the probablilty for introduction and spread

Mattilsynet considers a revision of the phytosanitary measures and priorities related to red core risk management. Mattilsynet has therefore asked VKM to do a risk assessment of the red core disease, especially focusing on the probability of spread through different pathways.

This risk assessment has been performed by VKM’s Panel on plant health. The assessment is based on an evaluation of available scientific documentation and data.

VKM conclusions

VKM’s Panel on plant health gives the following main conclusions:

• The pest of concern is the oomycete Phytohthora fragariae Hickman. The PRA area is Norway. P. fragariae is present in at least five limited regions of the PRA area. These regions are located in the counties of i) Hedmark, ii) Aust-Agder and Vest-Agder, iii) Hordaland and Rogaland, iv) Vestfold, and v) Møre og Romsdal. It is probable that the pathogen is present at some places of production without having been detected yet. The pathogen is regulated as a quarantine pest in the PRA area.
• With the current import regulations there is a medium probability of introduction of P. fragariae through import of infected Rubus plants for planting and a low probability of introduction through import of other consignments. However, there is little updated information available on the presence of the pathogen in different production systems, and there is only very limited evidence that the pathogen can spread by other means than strawberry plants. The level of uncertainty is therefore high.
• Without the current import regulations there would be a very high probability of introduction through the import of non-certified strawberry plants. The level of uncertainty of this assessment is low. The probability of introduction through import of certified strawberry plants is considered low, but without detailed information on the presence/absence of the pathogen in such material the level of uncertainty is high.
• With the current pest management procedures the probability of spread within the PRA area is medium for raspberry plants and machinery, other farm implements, footwear and animals. The probability of spread through other pathways ranges from low (legally traded, non-certified strawberry plants, seed potatoes, surface water, waterways and irrigation systems) to very low (remaining pathways). The level of uncertainty is low for certified strawberry plants and medium for legally traded, non-certified strawberry plants. Due to limited knowledge on the spread and survival of the pathogen, the level of uncertainty is high for all other pathways.
• Without the current pest management procedures the probability of spread with strawberry plants within the PRA area would be very high. The probability of spread with raspberry plants would be high and the probability of spread with seed potatoes, machinery, other farm implements, footwear, animals, surface water, waterways and irrigation systems would be medium. The probability of spread through other pathways would range from low to very low. The level of uncertainty is low for strawberry plants, but due to limited knowledge on the spread and survival of the pathogen, the level of uncertainty is generally high for all other pathways.
• All strawberry-growing areas in the whole PRA area are considered endangered areas.

VKM assessment procedure

An ad hoc-group consisting of both VKM members and external experts was appointed by the Panel on plant health to prepared a draft for final preparation by the panel. The members of the working group are acknowledged for their valuable contribution. The members of the ad hoc-group were: Leif Sundheim (chair and VKM member), Arild Sletten (VKM member), Trond Rafoss (VKM member) og Arne Stensvand (external expert, Bioforsk).