canada fleabane
Scientific Name: Conyza canadensis
Other names: horseweed, mare’s-tail and, vergerette du Canada
Family: Asteraceae or Compositae
General Description: Canada Fleabane is a winter or summer annual weed, reproducing only by seed.
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
- 10-180cm 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:
- Flowers are numerous on many short branches near the top of the main stem
- Flower heads 3-5mm across
- Ray florets are white but very short and usually concealed by the slightly longer involucral bracts around each flower head
- Disk florets are yellowish and are light 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
http://www.weedinfo.ca/en/weed-index/view/id/ERICA
http://omafra.gov.on.ca/english/crops/facts/ontweeds/canada_fleabane.htm
