Conyza canadensis

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Conyza canadensis

Binomial:Conyza canadensis
Conditions:Sun, dry to average moisture
Seed Dispersal:Wind-borne
Vegetative Spread:None

Conyza canadensis (formerly Erigeron canadensis L.) is an annual plant native throughout most of North America and Central America. Common names include Horseweed, Canadian Horseweed, Canadian Fleabane, Coltstail, and Butterweed.

Conyza canadensis seeds

Horseweed is a common weed of fields, meadows, wastes, and gardens throughout its native range, colonizing areas where perennials are not established. It often grows in cracks of hardscape surfaces as well, and can cause problems with heaving in thin materials such as flagstone.

It is an invasive species in Britain, found from northern Scotland to Cornwall. It is the only one of the British Conyza species that grows as a weed of arable land: the others are casuals of waste and disturbed ground in towns and by roads and railways. It is not invasive of any natural or semi-natural habitats.

Description[edit | edit source]

Horseweed is an annual plant growing to 1.5 m (5 ft) tall, with sparsely hairy stems. The leaves are slender, 2-10 (0.5" to 4") cm long and up to 1 cm (0.5") broad, with a coarsely toothed margin. The flowers are produced in dense inflorescences 1 cm (0.5") in diameter, with a ring of white or pale purple ray florets and a centre of yellow disc florets.

Ecology[edit | edit source]

Uses[edit | edit source]

Control[edit | edit source]

In summer, patrol upwind meadows and remove plants if possible.

  • Mowing: Provides effective control
  • Coppicing: fdfd
  • Pulling: Pulls easily, the root systems are rather compace and close to the surface.
  • Pre-emergents (organic): Pre-emergents can be used in spring
  • Contact herbicides (organic): Plants may regrow after burndown herbicides
  • Contact herbicides (synthetic): Non-resistant biotypes are susceptible to roundup.
  • Systemic herbicides (synthetic): Systemic herbicides such as glyphosate or paraquat are effective. Other systemics such as 2,4-D also are effective
  • Disposal: Safe for composting. Hot composting only after flowers are set.

References[edit | edit source]