Seasonal rhinitis, or hay fever, is an allergic reaction triggered by exposure to pollen. In Quebec, one person in five suffers from it, mainly due to ragweed pollen. Talking about ragweed as early as June is crucial to taking effective preventive measures before the plant produces allergenic pollen in August. In June, plants can be pulled out and infested areas mowed to prevent flowering and pollen dispersal.
Food of the Gods
Ragweed (Ambrosia artemisiifolia) is an annual plant of the Asteraceae family, native to North America. It takes its name from the Greek word ambrosia, meaning “food of the gods” (no, it’s not a joke!). It is recognized by its deeply cut leaves, which resemble those of carrots or celery. The plant’s stems are erect and often branched, reaching up to 1.5 meters (5′) in height. Ragweed flowers are small, green or yellow, and cluster in spikes at the end of the stems, appearing from July to September. This plant grows mainly in waste ground, roadsides, abandoned fields and disturbed areas.
Allergies
Ragweed mainly affects people allergic to pollen, asthmatics, children, people over 70 and outdoor workers. Symptoms of hay fever include frequent sneezing, rhinorrhea, nasal congestion, itching of the nose, throat and eyes, watery eyes, fatigue due to sleep disruption, coughing and aggravation of asthma. These symptoms have a major impact on quality of life, increasing the need for medical consultations and absences from work or school. Around 10% of the Canadian population and 15% of the American population suffers from ragweed pollen allergies, justifying proactive management efforts to reduce its impact on public health.
Treatment
To treat or prevent ragweed allergies, including hay fever, it’s advisable to limit exposure to pollen by staying indoors during periods of high pollen count, generally from July to September (yeah, right!). Use HEPA filters to purify indoor air, and close windows to keep pollen out. Shower and change clothes to remove pollen after going outdoors. Medical treatments include antihistamines, decongestants and nasal corticosteroids. Immunotherapy, or desensitization, can also be effective in the long term. For personalized advice, consult an allergist.
Distribution of Ragweed
Ragweed is widespread in North America, particularly in the Midwest and Northeast of the United States, as well as in Quebec and Ontario in Canada. It has been accidentally introduced into Europe, Asia and Australia, becoming a problem in several regions. In Europe, it is particularly present in France, Italy, Hungary and Switzerland, where it causes seasonal allergies similar to those observed in North America. As for Asia, it is present in Russia and parts of China, and is beginning to spread in these regions. In Australia, although less widespread, ragweed populations have been identified, often in disturbed areas similar to those colonized in North America and Europe.
Ragweed thrives in disturbed, well-drained soils. It is often found in vacant lots, roadsides, abandoned fields, construction zones and poorly maintained gardens. This invasive plant poses significant public health challenges due to its highly allergenic pollen, which causes seasonal allergies in many people. Its global spread requires coordinated management efforts to reduce its impact on public health and the environment.
Confusion With Goldenrod
Confusion between ragweed and goldenrod (Solidago spp.) is common due to their similar appearance from a distance and their coinciding flowering periods in late summer and early autumn. Ragweed, responsible for seasonal allergies, has deeply indented leaves and produces a light, wind-borne pollen. On the other hand, goldenrod, with its yellow panicle-like flowers and narrow leaves, is often wrongly accused of causing respiratory allergies, whereas its pollen is too heavy to be carried by the wind and depends on insects for pollination. Proper identification is essential for effective allergy management.
Propagation
Ragweed spreads mainly by its light seeds, enabling rapid colonization of new territories and disrupting local ecosystems. Seeds are dispersed by wind over long distances, by water during floods or heavy rains, and by human activities such as soil movement, construction, and the transport of contaminated material. Farm machinery, vehicles and clothing can also carry the seeds, facilitating their spread to various regions.
Controlling Ragweed
Various methods can be used to manage this invasive plant, ranging from mechanical techniques to chemical and biological interventions, as well as integrated management strategies.
Manual Removal
Effective for small infestations, it is important to remove plants before flowering to prevent pollen dispersal and seed formation. Using gloves and appropriate tools to avoid direct contact with the plant is crucial. This method ensures that the roots are also removed, thus preventing regrowth.
Mowing
Regular mowing of infested areas, such as vacant lots, roadsides and green spaces, prevents ragweed from flowering and producing seeds. This method is particularly effective when carried out several times a season, especially before the flowering period. It helps control the spread of the plant by limiting its ability to reproduce.
Planting Competitive Plants
Planting competitive plant species, such as grasses or ground cover, can reduce the space available for ragweed. These plants occupy the same space and use the same resources, preventing ragweed from establishing itself. This ecological method helps maintain local biodiversity while controlling ragweed.
Management of Disturbed Soils
Reducing soil disturbance can limit the spread of ragweed. Disturbed areas should be quickly stabilized with appropriate plantings to prevent ragweed invasion. Soil conservation practices such as mulching and ground cover are also effective in managing this invasive plant.
Use of Herbicides
Herbicide application may be necessary to manage heavy infestations. Herbicides must be applied before flowering to be effective. Contact your municipal authorities in the event of a major infestation, and use the services of a professional to assess the need for herbicides. Herbicides are a last resort.
Biological Control
Research is underway into the use of biological control agents, such as specific insects or pathogens, to manage ragweed populations. Although this method is promising, it requires in-depth studies to assess its effectiveness and ecological impacts. Biological control could offer a sustainable and environmentally-friendly solution in the long term.
Native or Noxious?
Although ragweed is native to North America, its elimination is often justified because of its significant impact on public health and the environment. As an aggressively spreading plant, it rapidly colonizes disturbed soils, disrupting existing ecosystems and competing with other native species for resources, which can reduce biodiversity and affect natural habitats. Its ability to colonize new territories makes it a threat to local ecosystems, justifying strict control measures. However, there are arguments against its complete elimination, as it is an integral part of certain ecosystems and contributes to ecosystem services such as soil stabilization and water filtration.
Composting
It’s generally best to avoid composting ragweed, especially if it’s flowering or carrying seeds, as the allergenic pollen may be released and the seeds may remain viable. If the compost can’t reach temperatures high enough (at least 55°C, 130?) to kill the seeds, it’s safer to dispose of ragweed with household waste, placing it in airtight plastic bags.
All of the photos need clear labelling. Only the first shows a good picture of ragweed. Several unidentified photos are of goldenrod, which does not contribute to hay fever discomfort.
The photo labeled “Ragweed in bloom with a view from above. Photo: vvvita” is not ragweed, it’s goldenrod. Best not to promote that common confusion between the two plants.