Ragweed (Ambrosia artemisiifolia) is a weed commonly found in Montréal. This
annual plant is present from May to September and dies when frost hits in the
fall. Its pollen causes hayfever or allergic rhinitis in one in six people,
which represents more than one million victims. Ragweed starts to spread
towards the end of July, however most of the pollen settles within a radius of
one kilometre around the plant.
How to identify ragweed
Ragweed is a plant that measures between 10 centimetres and 1.5 metres in
height. It can be identified by its jagged leaves that have 3 separate lobes.
It's yellow-green flowers are found in clusters at the top of the stem.
Where does ragweed grow?
It grows in poor soil. In an urban environment, it is often found on vacant
lots, in parking lots, along the edge of sidewalks, on playgrounds, at snow
dumps, on fill, in flower beds and along roads.
What symptoms does ragweed cause?
The allergen in ragweed is its pollen. The symptoms associated with the
- Allergic rhinitis: repeated sneezing, nasal congestion, clear
and abundant nasal discharge, itchy nose, palate and ears
red eyes, tearing, itchy eyes, swollen eyelids
- Asthma: coughing, wheezing
and shortness of breath
Quality of life can be disrupted from July to
September because of sleep problems, fatigue, irritability and trouble
If you have any medical questions about allergy symptoms, please call Info
Santé at 811.
How to control ragweed
The easiest and most accessible way is to systematically uproot ragweed
before it produces flowers towards the end of July. It is preferable to not
compost the plant because if seeds are present they could germinate.
Other control methods are also used: cutting and mowing are carried out once
in late July and once in late August. Planting herbaceous varieties can help to
compete with ragweed and produce its abundance. The use of mulch or a membrane
can also help to prevent the plant from spreading.
How to prevent it
People who are allergic to it are recommended to limit their exposure to
ragweed pollen by avoiding areas where it is abundant, and by avoiding outdoor
activities when the air concentration of pollen is very high between the end of
July and the end of September.
What is the difference between ragweed and poison ivy?
Ragweed and poison ivy are to undesirable plants because they are both
harmful to our health. Although they are two very different plants, they are
often confused. They differ in terms of appearance and symptoms they trigger.
Poison Ivy (Toxicodendron radicans)
- Its sap contains poisonous oil (urushiol) that causes painful
inflammation of the skin.
- Contamination can happen with direct or
indirect contact with the skin, because the oil can also stick to clothing
or to pets.
|Causes respiratory allergies.|
||Inflammation of the skin, redness and irritation, formation of
blisters on the affected areas.
||It is not dangerous to touch, however inhalation of its pollen can
cause allergic retinitis, conjunctivitis and asthma attacks.|
- A plant that can be ligneous, bushy, creeping or climbing.
leaves have a reddish tint in the spring, are dark green in the summer and
yellow, red or orange in the fall.
-One edge of the leaf is smooth and
the other side is irregularly jagged, its leaves are composed of 3
- The central petiole (small stem) on the middle leaflet is
longer than the other 2.
|- A herbaceous plant with very jagged leaves.|
- 10 cm to 1.5 m
- Has several flowers grouped together in a cob shape at the tip
of the plant.
- Its leaves resemble carrot leaves
It grows along the edge of the forest, on vacant properties, along
roads and trails, in parks or along waterways.
|It grows in poor soil for instance on vacant lots, along roads, in
A perennial, with reproduction through seeds and underground stems
An annual plant that dies every year and reproduces with
Caution: call a specialist to eliminate poison ivy. Do not burn the
plant or try to pull it out.
Ministère de la Santé et des Services sociaux du
Agence de la santé et des services sociaux de Montréal