Ragweed, an invasive plant that is problematic for both health and agriculture

Ragweed is native to North America but has spread to Europe in particular over the last few decades. Its pollen causes allergies, with between 1 and 3.5 million people believed to be affected in France. What is ragweed? Where is it found in France? What are its effects on agriculture? Are there ways of keeping it from spreading? Here is our update on the situation.  

What is ragweed?

Ambrosia is a genus of plants that includes around 40 different species, mainly native to the American continent. The best known and most widespread is common ragweed (Ambrosia artemisiifolia L.), an invasive plant that has been introduced into many parts of the world, including France and much of Europe. Three other species have also been introduced into mainland France: giant ragweed (Ambrosia trifida L.), western ragweed (Ambrosia psilostachya DC.) and lacy ragweed (Ambrosia tenuifolia Spreng.). They are considered to be emerging invasive plants and are also covered by ANSES's recommendations for action.

What are the health effects of ragweed pollen?

In an expert appraisal published in 2014, ANSES demonstrated that ragweed pollen is among the most problematic in France. This is because it is highly allergenic: it can induce allergy symptoms but also causes individuals to develop new allergies.

Ragweed pollen causes the same symptoms as other types of pollen in allergic individuals: sneezing, blocked nose, conjunctivitis, redness, swelling of the eyelids, etc. These symptoms heavily impact the quality of life of sufferers, with consequences on their social and professional lives, for example.

Ragweed allergy seems particularly debilitating compared with other pollen allergies according to a national survey of healthcare professionals (ANSES, 2020 – ragweed).

In 2020, ANSES estimated that between 1,115,000 and 3,504,000 people were allergic to ragweed pollen in mainland France and Corsica.

When do pollen levels peak?

The pollen peak occurs between mid-August and mid-September. Allergies caused by ragweed pollen therefore appear later than other pollen allergies, particularly those caused by grasses.

Where is ragweed found?

Native to North America, ragweed was first identified in the wild in Europe in the mid-19th century.

Today, the main allergy centres in France are in the Rhône and Loire valleys and in the south-west, particularly from the Tarn-et-Garonne to Charentes départements. Ragweed populations seem to have continued to spread increasingly rapidly and become denser in mainland France. The plant is now found across the entire country, with varying levels of infestation. There are three main types of infestation areas:

  • Areas with heavy infestation/establishment, including the Rhône, Isère and Drôme départements, but also Nièvre, Cher, Charentes and Tarn-et-Garonne;
  • "Frontline" areas such as the Yonne, northern Côte-d'Or and western Gard départements, located on the edge of the heavily infested areas;
  • Areas that are currently affected very little or not at all, such as Brittany, Normandy and Hauts-de-France.

Although it has been found in Guadeloupe and Martinique, ragweed is not considered invasive in these territories.

How does ragweed spread?

Its spread is favoured by certain human activities: the transport of ragweed-contaminated soil or seeds, agricultural and/or mowing machinery, animal feed, etc.

Common ragweed thrives in:

  • certain agricultural crops such as sunflower, soya or maize, where it causes considerable yield losses;
  • other environments such as riverbanks or roadsides.

What is the cost of the health impacts of ragweed?

In 2020, ANSES estimated the costs of the health impact associated with ragweed at a national level:

  • The cost of medical care (e.g. medicines and consultations) may be between €59 million and €186 million each year;
  • The cost of production losses based on absences from work may be between €10 million and €30 million per year.

These costs are expected to increase in the future, due to the expansion of ragweed-infested areas and an increase in pollen levels in ambient air, mainly as a result of climate change.

What are the effects of ragweed on agriculture?

The rapid growth of ragweed can have a major impact on the yield of certain crops due to competition for resources. This is particularly true of sunflowers, which are closely related to ragweed in the botanical classification (tribe Heliantheae). The proximity of the two species makes it difficult to eradicate the ragweed, either by chemical means or by sorting the seeds.

In 2011, economic losses in the European Union due to reduced agricultural production caused by ragweed were estimated to be €1846 million per year.

Does the spread of ragweed have an impact on biodiversity?

The presence of ragweed does not appear to have a significant effect on plant diversity in the colonised natural environments. For example, a 2014 study counted an average of 9.9 species in 4 m² plots on riverbanks invaded by ragweed and 10.6 species in neighbouring plots that had not been colonised. Several factors could explain ragweed’s lack of effect on biodiversity: it is an annual plant, which prevents it from forming dense, persistent colonies in the same place. It also prefers to colonise disturbed sites, where plant communities regrow each year from seeds stored in the soil.

What steps can be taken to keep it from spreading?


  • In your garden: pull the weeds out before flowering (end of summer) and take care to uproot the entire plant while wearing gloves. Do not do this if you are allergic or sensitive to ragweed;
  • If there are large amounts or for ragweed growing outside your property, send a report to

Building & public works and agricultural sectors:

  • Adopt good ragweed management practices such as cleaning machinery, limiting the amount of bare land and managing contaminated land.

Local authorities:

  • Act locally in frontline areas and areas still relatively unaffected by ragweed (northern third of mainland France) by immediately implementing specific (prefectural order) and coordinated regulations, and appointing a ragweed expert responsible for control measures on the ground.

Ragweed leaf beetle: a new arrival that could help with control

The ragweed leaf beetle (Ophraella communa) was spotted for the first time in the Lyon area in 2023. Its arrival in France could help combat ragweed and the allergies it causes. This insect, which is native to North America and was accidentally introduced into Italy in 2013, specifically attacks ragweed. It completely defoliates the plant leading to reduced production of pollen grains and seeds. In an expert appraisal published in 2019, ANSES estimated that introducing this insect into the former Rhône-Alpes region could reduce the allergic risk by more than 50%, leading to a 75 to 85% fall in the associated health costs. Damage caused by this insect to other plants, mainly sunflowers, appears to be limited. In addition, the beetle's larvae do not seem to be able to develop on plants other than ragweed. Monitoring is nevertheless needed to ensure that it does not adapt to native plants.