Ontario Weeds: Canada fleabane

Excerpt from Publication 505, Ontario Weeds, Order this publication
 

Table of Contents

  1. Scientific name
  2. Other names
  3. General description
  4. Habitat
  5. Seedlings
  6. Stems
  7. Leaves
  8. Flowers
  9. Often confused with/Distinguishing features
  10. References
  11. Related links

Scientific name:

Conyza canadensis

Other names:

Horseweed, mare's-tail and, vergerette du Canada

General Description:

Canada Fleabane is a winter or summer annual weed, reproducing only by seed.

Figure 1: Mature, fluffy flowers of Canada fleabane

Figure 1: Mature, fluffy flowers of Canada fleabane
Figure 2: Canada fleabane, hairy seedling leaves

Figure 2: Canada fleabane, hairy seedling leaves
Figure 3: Canada fleabane, seedling

Figure 3: Canada fleabane, seedling
Figure 4: Canada fleabane showing rosette of leaves

Figure 4: Canada fleabane showing rosette of leaves
Figure 5: Young Canada fleabane leaf

Figure 5: Young Canada fleabane leaf
Figure 6: Old, mature leaf of Canada fleabane

Figure 6: Old, mature leaf of Canada fleabane
Figure 7: Whole mature plant of Canada fleabane

Figure 7: Whole mature plant of Canada fleabane
Figure 8: Flowers of the Canada fleabane weed

Figure 8: Flowers of the Canada fleabane weed

Habitat:

Canada fleabane occurs throughout Ontario in grain fields, pastures, waste places, roadsides, and gardens.

Seedlings

  • Seeds are 1-2 mm long, almost transparent
  • Seeds are carried for long distances by wind via their attached pappus (parachute)
  • Most seedlings emerge from late August through October and overwinter, others emerge from March to early May
  • Seedling plant begins as a basal rosette

Stems:

  • Stems, erect
  • 10-180 cm (4in.-5ft) high
  • Hairy
  • Little branched

Leaves:

  • Seedling leaves are soft, hairy and bright green
  • Older leaves are much harsher
  • Narrowly oval, rarely more than 1cm wide
  • Taper to a slender stalk
  • Sparsely hairy leaves with smooth or slightly toothed margins
  • Gradually decreasing in size from base to top of plant

Flowers:

  • Flower are numerous on many short branches near the top of the main stem
  • Flower heads 3-5 mm across
  • Ray florets white but very short and usually concealed by the slightly longer involucral bracts around each flower head
  • Disk florets yellowish and fluffy at maturity.
  • Flowers from July to late autumn.

Often confused with / Distinguishing features:

Canada fleabane is easily distinguished by many narrow, bright green leaves and many small, yellow-green flower heads. The ray florets are inconspicuous and when mature the flowers look light and fluffy. When parts of the weed are crushed they have a faint odour that is similar to the scent of carrots.

Herbicide resistance

There are populations in Ontario that are resistant to:

  1. glyphosate (WSSA group 9)
  2. cloransulam (WSSA group 2)
  3. glyphosate (WSSA group 9) and cloransulam (WSSA group 2)
  4. paraquat (WSSA group 22)

References

Related Links

... on general Weed topics
... on weed identification, order OMAFRA Publication 505: Ontario Weeds
... on weed control, order OMAFRA Publication 75: Guide To Weed Control

 


For more information:
Toll Free: 1-877-424-1300
E-mail: ag.info.omafra@ontario.ca
Author: OMAFRA Staff
Creation Date: 01 June 2002
Last Reviewed: 12 December 2012