Sign Up for Updates
Integrated Crop Management
Integrated Crop Management
Sign Up for Updates

Horseweed (marestail)

Horseweed/marestail          Conyza Canadensis  (L.) Cronq.

Family:  Asteraceae (Composite family)
Life cycle:   Winter (primarily) and summer annual
Native status: Native to North America
Habitat:  Disturbed areas, no-till fields

General description:  Produces a basal rosette of hairy, irregularly toothed leaves 2-3 inches long.  Stem reaches heights of 6 ft, terminal portion is a large panicle of inconspicuous flowers producing numerous wind-dispersed seed.  Pubescent stem covered with alternately arranged, hairy leaves 3- 4 inches long

Key ID traits:  Hairy, lanceolate or linear leaves.  Lower leaves irregularly toothed.

Miscellaneous:  Horseweed is commonly called marestail in Iowa. In typical years, about ¾ of the population germinates in late summer/fall, the remainder the following spring.  It was the first weed to develop resistance to glyphosate in glyphosate resistant crops.  Resistance spread rapidly due to wind-dispersed seed.

seedlings
Seedlings form a rosette of pubescent, club-shaped leaves with irregularly toothed margins.
Dense stands of seedlings
Dense stands of seedlings are produced due to prolific seed production.

 

Elongating stems densely crowded with lanceolate leaves
Elongating stems densely crowded with lanceolate leaves.
Unbranched stems
Unbranched stems are topped with a conical inflorescence that produces small, wind-dispersed seed.
Dense horseweed monoculture
Horseweed is capable of forming dense monocultures in bare areas with no competing plants.
Authored by:
Bob Hartzler
Bob Hartzler
  • Retired Weed Scientist and Professor of Agronomy
Dr. Bob Hartzler is a former professor of agronomy and a former extension weed specialist with a Ph.D. in Crop Physiology from Iowa State University. He conducted research on weed biology and how it impacts the efficacy of weed management programs in corn and soybean. Dr. Hartzler also taught undergraduate classes in weed science and weed identification.
Meaghan Anderson
Meaghan Anderson
  • Field Agronomist in Central Iowa
Meaghan Anderson is a field agronomist in central Iowa and an extension specialist at Iowa State University Extension and Outreach. Areas of expertise include weed management, weed biology, cover crops, corn and soybean management, and integrated pest management.
Last Reviewed:

Topics:

Tags: