horseweed

Horseweed or marestail (Conyza canadensis). Photo: Betty Marose

Updated: July 21, 2021

Life cycle

Horeseweed, also called marestail, (Conyza canadensis) is an annual native plant, the seeds of which germinate in the spring and fall. 

Growth habit 

Erect 3 to 6 ft. tall, generally unbranched except at the top; leaves long and narrow with toothed margins, hairy, whorled around hairy stems

Reproduction

Seeds spread by wind; many small, white ray and yellow disk flowers

Conditions that favor growth

Primarily a weed of nursery crops and orchards, perennial crops, waste areas, and fallow fields

Seedlings

Horseweed seedlings

Photo: Bruce Ackley, The Ohio State University, Bugwood.org

Flowers

Horseweed flowers

Photo: Mary Ellen (Mel) Harte, Bugwood.org

Stems

Horseweed stems and foliage

Photo: Bruce Ackley, The Ohio State University, Bugwood.org

Management

Manual cultivation (it is very easy to pull) or maintain regular mowing to prevent flowers and seed production. It has been documented that horseweed is resistant to glyphosate a common ingredient in non-selective herbicides.