Undesirable Plants

Some plants can be harmful. It is important to learn how to identify and eliminate them, or to limit them to avoid inconvenience.


Ragweed (Ambrosia artemisiifolia L.) is a plant that is injurious to health. Its pollen causes hay fever, an allergy that affects about 18% of the population and whose symptoms are very uncomfortable—itching nose, repeated sneezing, tearing, nasal congestion, coughing and even asthma attacks. The best way to combat this nuisance is to pull out plants before they bloom, since each one can produce 3,000 seeds capable of propagating 600 new plants the following year. It is therefore important to inspect your property for ragweed and rip it out or mow it down.

Every year, the City of Vaudreuil-Dorion takes steps to eliminate ragweed in its territory by applying a selective, ecological herbicide. This product is totally natural and has no adverse effects on health or the environment. It attacks ragweed without causing damage to other plant life. Spreading this herbicide will significantly reduce the presence of the plant, mostly in vulnerable areas such as roadsides and bicycle paths, parks and potentially infested vacant lots. Vaudreuil-Dorion has been committed to fighting ragweed for several years. Results are positive and there has been a decrease in the incidence of ragweed since measures were introduced.

Under By-law no 1781 on nuisances, it is a nuisance to let ragweed grow on your property to the extent that it is detrimental to the neighbourhood. Ragweed must be pulled out or cut down before it matures, so that it does not release allergens.

Ragweed is an annual, so it dies during the fall frost. Its leaves are serrated and uniformly green. When it blossoms, the flowers are greenish-yellow and grouped at the top of the stem. It grows in poor soil and reaches a height of between 10 cm and 1.5 m.

Consult the fact sheet (in French) produced by the Direction de la santé publique de la Montérégie.

Poison Ivy

Poison ivy causes a painful inflammation of the skin and itching 24 to 48 hours after contact with the toxic substance in the plant. It is a very poisonous species and is found in various habitats ranging from woodland to cropland. Dry, rocky and sunny areas are especially favourable.

It is a perennial that can take various forms—bushy, creeping or climbing. Its glossy foliage changes from wine red in spring to dark green in summer, then to multicoloured in fall. The leaves are smooth or more or less serrated, and consist of three leaflets positioned alternately on the stem. The central petiole is longer than the other two. The plant measures from 20 cm to nearly 1 m in height. With protective gloves, you can destroy the plant by pulling it out and digging the soil to remove the roots.

See the fact sheet (in French) produced by the Government of Québec.

Japanese Knotweed

Japanese knotweed is an exotic species that is on the list of the 100 most invasive plants in the world! This plant greatly reduces surrounding plant biodiversity by its early-season growth and by the secretion of toxins that affect other plants. It has a hollow, green stem, mottled with red, and reaches a height of 3 to 4 metres and a width of 4 cm. Its alternating leaves are non-serrated, smooth and 10 to 25 cm long. It produces clusters of white flowers in late September.

Japanese Knotweed is already established on the territory of Vaudreuil-Dorion. If you come across this plant, it is essential to take measures to prevent it from spreading.

See the fact sheet (in French) put out by Comité Zip Jacques-Cartier to learn how to spot Japanese Knotweed and control it.

Giant Hogweed

Giant Hogweed was first recorded in Quebec in 1990. The extent of this plant in the region is still poorly known, but it is established in several places in Quebec. It can spread from a root tip or via its abundant seeds that have wide dispersal potential. Contact with the sap is not immediately painful, but large, burn-like skin lesions, activated by sunlight, may occur up to 48 hours after contact.

Consult the fact sheet (in French) put out by Comité Zip Jacques-Cartier to learn more about Giant Hogweed.

Invasive alien species and bodies of water

The video by the Ministère du Développement durable, de l’Environnement et des parcs suggests five simple, effective steps for cleaning boats used for sport fishing, sailing and recreation to prevent the introduction and spread of Invasive alien species in various bodies of water.

Espèces exotiques envahissantes : 5 étapes pour protéger son lac