EPPO Platform
on PRAs

ANSES Opinion and Report on conducting a risk analysis relating to the giant ragweed (Ambrosia trifida L.) in order to formulate management recommendations


Conclusion of the pest risk assessment


The contamination of seed lots or of maize, soybean or sunflower seed for livestock feed or the agri-food industry, imported from the area of origin of Ambrosia trifida into the PRA area, is regarded as the main factor for the introduction of this species. In addition, the volumes involved have been consistently high over the past few years. These imports are not covered by any particular regulations or controls with regard to their potential contamination by seeds of A. trifida. The regular entry of seeds of A. trifida in different localities in the PRA area therefore seems likely. On the other hand, the intentional introduction of Ambrosia trifida seeds is unlikely, and is regulated in France by the Decree of 26 April 2017. 


The establishment of A. trifida in the PRA area appears likely in all regions with warm and humid summers, especially in and on the edge of agricultural plots planted with maize, soybeans, sunflower or sorghum. In addition, the species can easily become established alongside water courses. Many of the countries of the European Union could therefore see the establishment of A. trifida in meso-hygrophilic environments, from south-west France, north-east Spain and northern Italy through to southern Germany and Poland and a large part of central Europe and the Balkans. The southernmost countries have summers that are too dry while the summers in the countries further north are not hot enough. Inside the PRA area, large populations are presently only observed in the plain of the Po river and in south-west France. 


The natural spread of A. trifida is slow and limited in distance, except in the case of hydrochory along a water course. However, the risk of long-distance spread by the transport of contaminated soil, crops and especially agricultural equipment used for harvesting infested crops seems very high. The risk of this species spreading from an infested site therefore seems very likely. 

Economic importance

From an agricultural point of view, the impact on contaminated plots is very rapid and can result in the total loss of the harvest and additional management costs for the plot. From a social and public health perspective, A. trifida contributes to the presence in the atmosphere of allergenic pollen that will only aggravate the issue of pollen-related allergies. This issue affects both the local population and the ability to attract tourism. The probability and magnitude of these impacts within the PRA area will depend on the species' ability to become established in the coming years, according to the different eco-climatic areas identified as favourable to its development.


  • Ambrosia trifida


Type File Size
Pest Risk Analysis Download 6,42MB

PRA Area

  • EU
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