Horseweed
Erigeron canadensis
Horseweed is a tall, weedy native annual with a single bristly stalk topped by clouds of tiny flowers; it is a prolific seeder and one of the first weeds to evolve widespread herbicide resistance.
- Light
- Full sun
- Water
- Low; drought-tolerant
- Difficulty
- Easy
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Overview
Horseweed (Erigeron canadensis, formerly Conyza canadensis), also called marestail, is an annual in the aster family native to North America. It typically grows as a single erect, bristly stem topped by a much-branched cluster of small, inconspicuous flower heads.
A classic weed of disturbed ground and no-till cropland, horseweed produces enormous numbers of wind-dispersed seeds and was among the first weeds to develop resistance to glyphosate herbicide, making it a major agricultural concern.
How to identify it
An erect annual ranging from 30 cm to over 2 m tall, usually unbranched until the flowering top.
- Stem: single, upright, rough with stiff hairs (bristles)
- Leaves: numerous, narrow, lance-shaped, hairy, crowded along the stem with little or no stalk
- Flowers: many tiny heads with greenish-white rays in a large, branched, terminal cluster
- Seeds: tiny with a tuft of bristles (pappus), dispersed in great quantity by wind
Care & growing
Not cultivated; managed as a weed.
- Light: full sun
- Water: drought-tolerant; thrives on dry, disturbed soils
- Soil: tolerates poor, compacted and disturbed ground
- Temperature: germinates as a fall or spring annual depending on region
- Propagation: by abundant wind-blown seed
Control young rosettes early by cultivation or herbicide; because of widespread glyphosate resistance, integrated tactics — cover crops, tillage and alternative herbicides — are recommended.
Habitat & origin
Native to North and Central America, horseweed has spread as a weed worldwide. It colonizes disturbed, open ground — fields, no-till cropland, roadsides, construction sites, fallow land and waste places.
It is an early colonizer of bare soil and a significant weed in conservation-tillage farming systems.
Frequently asked questions
Why is horseweed hard to control?
It produces vast numbers of wind-dispersed seeds and has evolved resistance to glyphosate and some other herbicides, so it requires integrated, multi-tactic management.
Is horseweed the same as marestail?
Yes — marestail is just another common name for the same plant, Erigeron canadensis.
When should I control horseweed?
Target it early, at the small rosette stage in fall or spring, before it bolts into a tall stem that is far harder to kill.
Is horseweed native?
Yes, it is native to North and Central America, though it has since spread as a weed across much of the world.
Horseweed guides
In-depth guides for identifying, growing, and caring for Horseweed.
