Ragweed: an exotic, invasive and allergenic plant
Updated on 16/07/2018
Ragweed, Pollens, Allergy, Biological pest control
Over the last few decades, allergies have become increasingly prevalent in the population in many countries, and especially in France. Pollen of the ragweed, which is an invasive exotic plant, causes allergic reactions in many people. ANSES is examining several species of ragweed in order to contribute to the prevention and management of their introduction and propagation. It is evaluating the risk of propagation of different ragweed species, and has also been asked to assess the risk of introduction of the small Ophraella communa beetle as a biological control solution to ragweed.
Allergies have become increasingly prevalent in the population in many countries, including France. The number of people suffering from allergies has more than doubled in the last twenty years.
Pollen allergies (pollinosis, also known as hay fever or allergic rhinitis) currently affect 15 to 20% of the French population. In a collective expert assessment report published in 2014, ANSES showed that ragweed pollen was among the most problematic plant pollens France. In fact, the pollen from this plant is both highly allergenic (allergy-causing) and an allergen (substance causing an allergic symptom). Five grains per cubic meter of air are enough to bring about symptoms.
The allergies caused by ragweed pollen occur late in the season. They usually begin in mid-August, with the greatest intensity in September, stretching on into October.
Several different ragweed species of the Ambrosia genus are present in France. The most well-known and widespread species is the common ragweed (Ambrosia artemisiifolia L.) but the giant ragweed (Ambrosia trifida L.) is also found, as well as the perennial ragweed (Ambrosia psilostachya DC.).
These types of ragweed are exotic invasive species. In fact, they were introduced into Europe from America, which is their natural range, via contaminated batches of cereal seed.
Analysis of the risks linked to the A. trifida and A. psilostachya ragweed species
In 2014, the European Parliament and European Council published a regulation on the prevention and management of the introduction and propagation of exotic invasive species. This regulation contains a list of species for which coordinated prevention and control actions should be implemented between the member States of the European Union. These actions aim to reduce the negative impact of these species on biodiversity, pollination, the regulation of waterways, etc., as well as other possible negative effects including allergies.
In order to add a species to this list of invasive species in the European regulation, the European Commission must obtain an analysis of its risk. And so ANSES has conducted a risk analysis for the two ragweed species, A. trifida and A. psilostachya.
The risks linked A. trifida are very different from those of A. psilostachya. The ecological and biological characteristics of A. psilostachya and the fact that it has been present in Europe for quite some time in an area that has remained highly circumscribed leads us to conclude that the risk of invasion by this species and the risk of it being reintroduced in the current state of international trade is relatively low.
In contrast, the risks linked to A. trifida are much higher. Introduction from the area of origin is difficult to control. Numerous eco-climatic zones favourable to the species are found throughout Europe in areas where cropping systems have developed which could facilitate the species’ development. Due to the great difficulty of fighting A. trifida in non-agricultural environments and the allergenicity of its pollen, it is a proven threat to human health and to the environment.
Ophraella communa: a beetle to control ragweed?
Ophraella communa, whose common name is the ragweed leaf beetle, belongs to the Chrysomelidae family of leaf beetles. Originating in North America, this beetle feeds on plants of the Asteraceae family to which the ragweed species belong, as well as cultivated plants such as the sunflower and the Jerusalem artichoke.
This insect was sighted for the first time in Europe in the summer of 2013 on common ragweed plants in a large area spanning from parts of northern Italy to southern Switzerland.
In the framework of the two formal requests for assessment of the risks linked to the natural introduction of O. communa and those associated with its use in biological pest control, ANSES has concluded that the risk of O. communa with regard to sunflower and Jerusalem artichoke crops, and more widely for the environment as a whole, has been found to be acceptable. However, the oligophageous nature of O. communa requires prudence as to its use as an inundative release biological control agent. ANSES recommends that surveillance of O. communa introduction be conducted and that sunflower crops be monitored if O. communa introduction is found to have occurred.
ANSES assessment of pollen in ambient air
In 2014, ANSES produced a full report on the current state of knowledge of pollen in ambient air in mainland France. This assessment work has shown that:
The most problematic pollens in France come from true grasses (Gramineae), the birch family of trees (Betulaceae), ragweed and the cypress (Cupressaceae) family of trees (including cypress, thuya and juniper, for example);
It is not currently possible to determine a level at which effects will appear for a given type of pollens, due to the fact that the dose-response relationship involves numerous factors, such as the pollen's allergenicity, individual sensitivity, etc.;
Climate change may influence pollinisation starting dates in a number of plant species, prompting it to begin earlier and therefore prolonging the pollinisation period.
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