EPPO Global Database

Ambrosia trifida(AMBTR)

EPPO Datasheet: Ambrosia trifida

Last updated: 2020-09-09


Preferred name: Ambrosia trifida
Authority: Linnaeus
Taxonomic position: Plantae: Magnoliophyta: Angiospermae: Campanulids: Asterales: Asteraceae: Asteroideae
Common names in English: buffalo weed, crownweed (US), giant ragweed (US), great ragweed, horseweed (US), wild hemp (US)
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EPPO Categorization: A2 list
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History of introduction and spread

Ambrosia trifida is native to North America where the species is recorded as being weedy in many states (USDA, 2020). In North America, A. trifida seems to prefer establishment at latitudes between 45° and 30° north because of fairly strict photoperiodic constraints for flowering, which may maximize its reproduction (Allard, 1943).

Ambrosia trifida was introduced into the EPPO region at the end of the 19th century, and it has expanded its range since the mid-1900s (Moser & Essl, 2013; Chauvel et al., 2015). Many of the occurrences of A. trifida in the EPPO region are considered casual populations. There are, however, well-established populations in western Europe, with high densities in south-west France (Chauvel et al., 2015). It is also considered established in a large part of Italy.

In Japan, the first record was in 1952 from the Shizuoka Prefecture (Honshu) and now A. trifida occurs in almost the entire country. In South Korea, A. trifida was first recorded in the Seoul metropolitan area during the 1970s and it is now widely naturalized in the country (Kim, 2017). Qin et al. (2014) detail that A. trifida was introduced into China in 1935 from North America. For China, the literature reports differences in the number of provinces where A. trifida occurs, for example Xu et al. (2012) list five and Wan et al. (2012) lists 12.

EPPO Region: Austria, Belarus, Belgium, Czech Republic, Denmark, Estonia, France (mainland), Georgia, Germany, Ireland, Italy (mainland), Latvia, Lithuania, Moldova, Netherlands, Norway, Poland, Romania, Russia (Central Russia, Southern Russia), Serbia, Slovakia, Slovenia, Spain (mainland), Switzerland, United Kingdom
Asia: China (Beijing, Hebei, Heilongjiang, Hubei, Hunan, Jiangxi, Jilin, Liaoning, Neimenggu, Shandong, Xinjiang, Zhejiang), Japan, Korea, Republic, Mongolia
North America: Canada (Alberta, Manitoba, New Brunswick, Nova Scotia, Ontario, Prince Edward Island, Québec, Saskatchewan), Mexico, United States of America (Alabama, Arizona, Arkansas, California, Colorado, Connecticut, Delaware, Florida, Georgia, Idaho, Illinois, Indiana, Iowa, Kansas, Kentucky, Louisiana, Maine, Maryland, Massachusetts, Michigan, Minnesota, Mississippi, Missouri, Montana, Nebraska, New Hampshire, New Jersey, New Mexico, New York, North Carolina, North Dakota, Ohio, Oklahoma, Oregon, Pennsylvania, Rhode Island, South Carolina, South Dakota, Tennessee, Texas, Utah, Vermont, Virginia, Washington, West Virginia, Wisconsin, Wyoming)

MORPHOLOGY 2020-09-09

Plant type

Annual herbaceous.


Ambrosia trifida has large leaves (4-15 cm long). They are oppositely arranged, simple and palmately lobed, generally with three lobes (they may also have five lobes or be unlobed). The upper leaves can be alternate. They are borne on a long petiole (3–12 cm). Male and female flowers are separated on the same individual (monoecious plant). The inflorescences are long terminal clusters (30 cm) consisting of florets of male flowers. The female flowers are grouped into florets at the base of the male clusters and sometimes in the axils of the upper leaves. The fruit is a cup-shaped cypsela, tipped with a long central beak surrounded by a crown of approximately five or more shorter tips. It measures from 0.5 to 1.2 cm long and from 0.3 to 0.5 cm wide. A. trifida is characterized by enormous variability in the size and shape of its seeds, which may correspond to an ability to germinate in a variety of conditions (Harrison et al., 2007; Hovick et al., 2018).



Ambrosia trifida has a comparatively low fecundity (compared to other Ambrosia species), transient seed-bank characteristics and a high percentage of non-viable seeds (Harrison et al., 2001, 2007). Goplen et al. (2016) detail that plants produced an average of 1800 seeds per plant in soybean and field margins, with 66% being potentially viable. The majority (90% or more) of A. trifida seeds buried 10 cm or less lost viability after 4 years (Stoller & Wax, 1974; Harrison et al., 2007); however, some seeds remained viable for 9 to 21 years when buried 20 cm or deeper (Toole & Brown, 1946; Harrison et al., 2007). Because of their high nutritional value, the seeds are often eaten by animals (e.g. birds and rodents), causing high losses (Harrison et al., 2003). It should be noted that A. trifida only reproduces by seed and not vegetatively.

Within the EPPO region and the native range, seedlings typically emerge early in the growing season (e.g. March) and over a prolonged period (March until the end of July; Regnier et al., 2016). Flowering occurs in response to shortening day length and begins in the male inflorescences (Allard,   1943).   In   the   native   range   (North   America), A. trifida flowers from mid-June to the end of August, or even early September (Bassett & Crompton, 1982). The species can flower 2–3 weeks earlier than A. artemisiifolia. In south-west France, the flowering dates observed are similar to those in its area of origin (B. Chauvel, pers. comm., 2019).


In North America, A. trifida grows in different types of herbaceous communities, including ruderal habitats such as railroad embankments, roadsides  and cultivated  fields, on rather rich and moist soil (Bassett & Crompton, 1982; Hartnett et al., 1987; Krippel & Colling, 2006; Regnier et al., 2016). It is also found in damp natural environments, particularly on riverbanks and floodplains as well as managed moist environments such as the banks of irrigation ditches and waterways (Sickels & Simpson, 1985; Regnier et al., 2016).

In Japan, A. trifida can be found predominantly along riverbanks, mostly in disturbed locations (artificial banks, bridges and quarries) but also in the riverine vegetation (Miyawaki & Washitani, 2004). In South Korea, it occurs in the riparian systems of streams and rivers and around agricultural fields, on road edges and landfill sites and, recently, it has also invaded forest edges and interiors (Lee et al., 2010). In Japan and South Korea, A. trifida grows also in semi-natural areas (Miyawaki & Washitani, 2004; Lee et al., 2010).

Suitable habitats occur for the establishment of A. trifida in the EPPO region. It currently occupies different environments: agricultural land (Rydlo et al., 2011), the banks of major water courses such as the Rhine and the Elbe, the banks of  streams   or  canals  (Jehlík & Hejný,  1974), road networks and other disturbed environments (e.g. abandoned industrial sites), as well as green urban areas (gardens; Moser & Essl, 2013).

For A. trifida, most natural habitats of high conservation value are unsuitable, and thus negative effects of this plant on biodiversity are considered to be of low importance. Nevertheless, some data are available on A. trifida showing that it is able to invade natural riverside vegetation. There are no data for negative impacts of the species on rivers, especially for where it occurs in the Po Valley (Italy) in the EPPO region. In Central and Eastern Europe, A. trifida mainly occupies ruderal habitats including railway tracks and cultivated fields (Rydlo et al., 2011). According to Stoyanov et al. (2014), A. trifida may be established around Robinia pseudoacacia bushes close to the railway at the exit of the town of Dalgopol (Bulgaria). In Western Europe (France), the species only occupies cultivated fields.

Environmental requirements

A. trifida is not well adapted to drought, and it is not recorded in areas with a long summer drought unless there is irrigation (Allard, 1943; Regnier et al., 2016). Establishment is favoured by moist environments. A. trifida can tolerate a wide variety of soil types (Regnier et al., 2016).

Seeds germinate under a wide range of temperatures with an optimum germination between 10 and 24°C (Abul-Fatih & Bazzaz, 1979). The seedlings can develop quickly within 4 to 13 days (Abul-Fatih & Bazzaz, 1979). A. trifida can emerge over a long period of time (March to June/July). In France, it emerges together with spring crops or a few days after crop emergence. Soybean is seeded in May in France. In south-west France, germination and emergence can begin as early as the end of March and continue later until the end of summer, especially in irrigated fields (Mamarot & Rodriguez, 2014). A. trifida has high photosynthetic ability compared to most annual species (Barnett & Steckel, 2013). It is damaged (i.e. damage to the foliage), but not killed by moderate frost.

In North America, there is variation in A. trifida plant traits at both large and small geographic scales. Populations in the western USA corn belt had nearly four times greater fecundity and a 50% greater allocation to reproduction than populations in the eastern USA corn belt (Hovick et al., 2018). In addition, seedling emergence patterns  differ among populations in agricultural fields (Sprague et al., 2004; Schutte et al., 2006, 2008). For example, the latter author showed that seeds which were from Iowa (western USA corn belt) produced seedlings in a rapid flush during early April, whereas seeds from Illinois and Ohio (eastern USA corn belt) produced seedlings in a more gradual flush that extended into late  July. Seedling emergence patterns also differ between agricultural and non-agricultural environments. Populations from agricultural habitats exhibited a more prolonged emergence pattern than those from riparian, early successional, railroad siding or forest border habitats (Schutte et al., 2012; Hovick et al., 2018).

Natural enemies

There are no known natural enemies in the EPPO region.

Uses and benefits

There are no known uses and benefits of A. trifida for the EPPO region.


Globally,  there  have   been   numerous  interceptions  of A. trifida as a contaminant of seed or as a contaminant of grain (Shamonin & Smetnik, 1986). A. trifida has been introduced in Europe with imports of animal feed and seed. There are documented cases of the introduction of A. trifida into the EPPO region (Europe) via seed from crops imported from North America (Moser & Essl, 2013; Chauvel et al., 2015). This includes contamination of spring wheat seed for planting (Moser & Essl, 2013), soybean seed (Chauvel et al., 2015), maize seed (Stoyanov et al., 2014; Chauvel et al., 2015; COSAVE, 2019) and seed of other spring crops (sunflower, sorghum; G. Fried, pers. comm., 2019).

IMPACTS 2020-09-09

Effects on plants

A. trifida is highly competitive and can form annual monospecific stands in ruderal habitats, forest borders, grassland habitats and riparian habitats (Sickels & Simpson, 1985; Regnier et al., 2016).

In agricultural environments, the plant’s significant and rapid development gives it a strong ability to enter into competition with different summer crops: soybean, cotton and maize. Even at very low densities (one plant per 25 m2), loss of crop yield (of around 5%) has been shown, a phenomenon rarely observed for other weeds (Harrison et al., 2001). Yield reductions of 13–50% have been observed in crop situations, with the losses being greatest when the crop and the weed grow simultaneously (Harrison et al., 2001; Barnett & Steckel, 2013). In North America, complete crop losses have been reported due to the presence of A. trifida (E. Regnier, pers. comm., 2019).

In 1994, Webster et al. (1994) estimated the loss of yield in the USA associated with A. trifida in soybeans to be 5– 7% of the yield of the crop. A recent study (Regnier et al., 2016) among farmers in the USA showed that A. trifida was the most difficult weed to manage for 45% of them, while 57% also reported a problem of herbicide resistance, either to acetolactate synthase (ALS) inhibitors or glyphosate (or resistance to both).

In Northeast China, A. trifida is considered one of the weeds that causes the most economic damage to wheat and other annual crops. It was found that the plant and its residues have allelopathic effects that reduce wheat growth (Kong et al., 2007).

In Europe, it is not currently possible to quantify the economic impacts of this species. In France, in the region of Toulouse, farmers report additional costs associated with hand weeding, and even the destruction of plots before harvesting due to very high densities of plants, meaning the total loss of the crop (A. Rodriguez, pers. comm., 2017). These costs (from a few hundred euros to a few thousand euros per hectare) have not yet been studied to a precise enough degree. At the national level, given the limited distribution of the species and the highly localized nature of the existing populations in the EPPO region (Moser & Essl, 2013; Chauvel et al., 2015), the costs in terms of health or losses of agricultural yields attributable to this species are negligible so far.

Any action targeting control of this species will generate additional production costs (cost of weeding practices, establishment of less profitable crops or fallow). In the absence of plant health regulations relating to the control of introduction into the EPPO region of seed lots of maize, soybeans, sorghum and sunflower, the risk of introduction of herbicide-resistant genotypes of A. trifida appears high and such an introduction would result in a very high increase in control costs based on the studies carried out in the USA (Ganie et al., 2017).

In annual summer crops where it is present, A. trifida is managed like other weeds without it being subject to additional control measures. Note, however, the arrival on the European market of sunflower varieties tolerant to herbicides intended to control species of the genus Ambrosia (and Asteraceae more generally). These varieties, through their tolerance to two herbicides from the class of ALS inhibitors, enable weed control in a post-emergence situation; they were placed on sale in 2010 to improve the post- emergence weed control of sunflower crops in general and more specifically against A. artemisiifolia. These new varieties make it easier to manage the recent problems with A. trifida. However, the repeated use of such varieties and the associated herbicides risks causing the significant and rapid selection of populations of A. trifida resistant to these active ingredients in the PRA area, as is currently occurring with A. artemisiifolia (Chauvel & Gard, 2010). An additional problem is the emerging resistance of A. trifida to glyphosate and ALS-inhibiting  herbicides  (Norsworthy et al., 2011; Regnier et al., 2016), thus further decreasing the possible avenues for its control, both in agriculture and ruderal areas, such as railways, roadsides etc.

Based on  the results of studies conducted in the  USA (Ganie et al., 2017) in 2013 and 2014, the absence of management measures against this species resulted in a total loss of maize yield, even at low weed densities. These results suggest the same level of impact in the PRA area if no control measures are implemented against A. trifida.

Without the implementation of integrated control against this species – effective chemical weed control, rotation including winter crops and appropriate tillage – the negative effects of A. trifida will probably increase, as suggested by the situation with certain plots in south-west France. However, until now, no published information has been available to quantify the negative effects of A. trifida in the PRA area.

Some countries, such as Russia, Israel and Egypt, refuse imports of cereals contaminated by species of the genus Ambrosia. A. trifida is not mature when winter cereals are harvested in Europe and will not directly contaminate these crops. On the other hand, it is mature at the time of harvesting summer crops (maize, soybean, sunflower and sorghum). Contamination of these crops could prevent their export. As an example, in 2015 the maize export sector from the EU accounted   for  more than  63 million  tonnes (EUROSTAT, 2019). There is a great risk of the additional costs of weed control and/or post-harvest sorting being reflected in market losses due to a higher production cost compared with situations free from A. trifida.

Environmental and social impact

For A. trifida, most natural habitats of high conservation value have a low potential to be invaded as they have low levels of disturbance, and thus the negative effects of this plant on biodiversity are considered to be of low importance. Nevertheless, some data are available on A. trifida showing that it is able to invade natural riverside vegetation. There are no data for negative impacts of the species on rivers, especially for where it occurs in the Po Valley (Italy) in the EPPO region. However, there is some anecdotal evidence that the species may have impacts on biodiversity from online forums (e.g. Acta Plantarum, an Italian forum for botanists: https://www.floraitaliae.actaplantarum. org) where comments include that the species has increased from 1 to 100 plants in one year.

In Japan, a study on the floral diversity of infested river banks highlighted a decrease in diversity as a function of the density of A. trifida (Washitani, 2001). Miyawaki and Washitani (1996) found that plant species diversity was negatively correlated with the abundance of A. trifida in a nature reserve of moist tall grasslands along the Arakawa River, near Tokyo/Japan. Lee et al. (2010) demonstrated that the vegetation dominated by A. trifida in South Korea differed with regard to the composition and diversity of the species to that of the uninvaded riparian vegetation.

There is limited data on the impact of the species on habitats, except those on the problems of rehabilitation of fragile grassland environments in the USA (Megyeri, 2011). There is very little data on the invasion area on the environmental impact of infestations of A. trifida.

In the USA, A. trifida has been identified as a public health problem since the 1930s due to its allergenic pollen and its presence in urban areas. Historically, Gahn (1933) had already indicated that hundreds of thousands of people were affected by allergy problems without any quantified costs being mentioned. The allergens are well known (Goldstein et al., 1994). Today, A. trifida (and its congener A. artemisiifolia) are the main cause of seasonal allergic rhinitis in eastern and middle USA. The Ambrosia pollen also contributes to the exacerbation of asthma and allergenic conjunctivitis (Oh, 2018). It is recommended that individuals allergic to Ambrosia pollen may adjust their outdoor activities to avoid contact with the allergen (e.g. https://www.aafa.org/ragweed-pollen/). The health effect remains significant to such a point that visitor numbers at certain tourist sites are affected according to the presence of species of the genus Ambrosia. Consequently, tourism can be impaired if visitors avoid areas with high Ambrosia occurrence (Durham, 1949).

CONTROL 2020-09-09

At the plot scale, it is technically possible to achieve total control of A. trifida by a combination of chemical and mechanical weed control and agronomic practices. Currently, the development of resistance to herbicides, particularly to ALS inhibitors and glyphosate, is reducing the effectiveness of control (Heap, 2017). Moreover, supplementary mechanical management is not really feasible on a large scale. At the regional scale, it is likely that the spread cannot be reliably prevented, as shown by the progression of A. trifida on the North American continent (Royer & Dickinson, 1999).


In the EPPO region, A. trifida is is included on the EPPO A2 list of pests recommended for regulation as a quarantine pest. It is also listed by the Eurasian Economic Union (A2 List).

All Ambrosia species are regulated in Directive 2002/32/ EC as undesirable substances in animal feed. In the EU, grain intended for bird feed is subject to regulations that severely restrict the presence of seeds of species of the genus Ambrosia (50 mg kg-1 of grain, Regulation (EU) 2015/186 of 6 February 2015).

In the USA, A. trifida has the status of ‘restricted noxious weed’ in four states (California, Delaware, New Jersey and Wisconsin) under the Federal Seed Act (USDA, 2018) and the status of ‘noxious weed’ in four states [California, Delaware, Illinois  and  Minnesota   (in two counties  only)] under the Federal Noxious Weed Act and Minnesota Noxious Weed Law (USDA, https://plants.usda.gov/java/ noxComposite?stateRpt=yes; Minnesota Department of agriculture, https://www.mda.state.mn.us/plants/pestmanageme nt/weedcontrol/noxiouslist/countynoxiousweeds).

In Canada, A. trifida is listed as a ‘primary noxious weed’ under the Weed Seeds Order of the Seeds Act (http://www.gazette.gc.ca/rp-pr/p2/2016/2016-05-18/html/sor-dors93-eng.html) and as a ‘noxious weed’ under the noxious weed laws in the provinces of Ontario, Quebec, and Manitoba (Ontario Ministry of Agriculture, Food and Rural Affairs, http://www.omafra.gov.on.ca/english/crops/ facts/info_ragweed.htm).


REFERENCES 2022-01-10

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This datasheet was produced following an expert working group that risk analysed A. trifida for the EPPO region in February 2019. The composition of the expert working group was D. Chapman (Stirling University, GB), B. Chauvel (French National Institute for Agricultural Research, FR), S. Follak (AGES, AT), G. Fried (ANSES, FR), Y. Kulakova (All-Russian Plant Protection Center, RU), D. Marisavl Jevic (Institute for Plant Protection and Environment, RS), E. Regnier (Ohio State University, US), U. Starfinger (Julius  K€uhn  Institut,  DE), V.  van   Valkenburg (National Plant Protection Organisation, NL) and R Tanner (EPPO).

How to cite this datasheet?

EPPO (2024) Ambrosia trifida. EPPO datasheets on pests recommended for regulation. https://gd.eppo.int (accessed 2024-04-13)

Datasheet history 2020-09-09

This datasheet was first published in the EPPO Bulletin in 2020 and is now maintained in an electronic format in the EPPO Global Database. The sections on 'Identity' and 'Geographical distribution' are automatically updated from the database. For other sections, the date of last revision is indicated on the right.