Horseweed Identification Guide

Horseweed is an erect winter annual weed that is problematic in most Mississippi row crops.  This species emerges in early fall and forms a rosette throughout the winter.  In spring, horseweed begins to elongate upward and may persist through early summer.  Like many other winter annual weed species, fall-applied residual herbicides are effective in preventing emergence of horseweed.  Emerged horseweed in fall and early-spring is best controlled with 2,4-D or dicamba.  Many populations across Mississippi are resistant to glyphosate and paraquat. Recognizing this weed at early developmental stages allows for prompt herbicide applications and improved control.

• Latin name: Conyza (sometimes Erigeron) canadensis (L.) Cronq.
• Family: Asteraceae (Sunflower)
• Life cycle: Winter annual
• Synonyms: Marestail or mare’s tail, Canadian fleabane, hogweed

Identifying Characteristics

• Cotyledons have smooth margins and appear to lack veins.
• Leaves on older plants are linear, alternate, exhibit toothed margins, and are attached directly to the stem.
• Stems can reach up to 6.5 ft and are covered in bristly hair.
• Inflorescences (flowers) are numerous and are arranged along an elongated panicle. These florets are often white to lavender in color and even yellow in some instances.
  

  Seedling horseweed. Credit: Univ. of Missouri Div. of Plant Sciences.

Horseweed in basal rosette stage. Credit: Univ. of Missouri Div. of Plant Sciences.

Credit: Dr. Jason Bond

Seedling horseweed. Credit: Univ. of Missouri Div. of Plant Sciences.