Ministry of Agriculture, Food and Rural Affairs

Table of Contents

Names

•English - common ragweed, giant ragweed
•French - petite herbe à poux, grande herbe à poux
•Latin - Ambrosia artemisiifolia L., Ambrosia trifida L.

Photos

Figure 1. Common ragweed (A - plant beginning to flower; B - spikes of male flower heads ready to release pollen).

Figure 2. Giant ragweed

Current Status

•Ontario Weeds Act - noxious
•Other provinces - noxious in Quebec, Manitoba, Saskatchewan (common only)
•Canadian Federal Seeds Act - giant class 2, common class 3
•U.S. Federal Noxious Weed - no
•U.S. Noxious State Reg - common 3 states, giant 5 states (including Illinois, Minn for both sp.)

Poisonous/Cautions

•Pub 505 - Pollen causes hayfever
•NE Weeds - Pollen from ragweed is a primary cause of hay fever.
•Canadian Poison Plant - not listed
•Cornell Poison Plant - not listed

Distribution

•Common ragweed is common in all parts of southern Ontario and giant ragweed is found in south western Ontario. A common weed in disturbed soils or where the overstory of tree and shrub growth has been removed.

Growth Habit

•Annual

Method of Propagation

•Seeds

Control

•Susceptible to 2,4-D, dicamba, glyphosate and a number other in crop herbicides. Common ragweed is listed on the label of many herbicides. Some labels also include giant ragweed. A single mowing will delay but not prevent flowering. Repeated mowing is necessary to prevent pollen release.

Other Comments

•Giant ragweed flowers (sheds pollen) in mid July and common ragweed flowers in mid August.

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