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Ragweed or poison ivy?

Ragweed (Ambrosia artemisiifolia) - young seedling
Photo: Pascale Maynard
Ragweed (Ambrosia artemisiifolia) - young seedling
  • Ragweed (Ambrosia artemisiifolia) - young seedling
  • Ragweed (Ambrosia artemisiifolia)
  • Ragweed (Ambrosia artemisiifolia) - beginning of flowering
  • Ragweed (Ambrosia artemisiifolia)
  • Ragweed (Ambrosia artemisiifolia) - inflorescence
  • Ragweed (Ambrosia artemisiifolia) - male flowers releasing pollen

In French, some confusion exists between poison ivy (herbe à la puce) and ragweed (herbe à poux) mainly because of their similar sounding vernacular names. However, these plants are quite distinct and cannot be confused one for the other. The problems they cause are also very different.

Contact with poison ivy may cause skin reactions while the pollen of ragweed may cause respiratory allergies.

Ragweed – A real nuisance

Many people are highly allergic to ragweed pollen.

There are two types of ragweed in Quebec: giant ragweed (Ambrosia trifida) and common ragweed (Ambrosia artemisiifolia). Common ragweed is the most widespread species and is the main cause of hay fever from late July until the first frosts. It has deeply divided leaves and the male flowers produce huge amounts of very light pollen that can be carried over 200 km by the wind!

It grows in colonies in poor, disturbed soil: along roads, in vacant lots and on lawns burned by calcium. It is an annual that reproduces by seed. The seeds can survive in the soil for as long as forty years, so it is important to tear the plant before August, to prevent it from flowering. Another proven method is to reseed invaded sites with more competitive species, including buckwheat, bluegrass, clover or meadow mixture.

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