WSU Extension

Hortsense

Weeds : Horseweed (Marestail) : Conyza canadensis
(revision date: 2/12/2019)

Family: Asteraceae (Compositae)
Cycle: Annual
Plant Type: Broadleaf

Use Integrated Pest Management (IPM) for successful weed management.

Biology
Horseweed plants range from one to five feet tall. The erect stems may be branched, especially near the top. The alternate, rather narrow leaves are one to three inches long and closely crowded on the stems. The leaf surface is hairy. Lower leaves typically have short petioles and may be slightly toothed; upper leaves usually lack petioles and are smooth-margined. The small, inconspicuous greenish-white flowers are borne at the tips of stems in mid- to late summer. SPECIAL INFORMATION: The leaves and flowers of horseweed contain a compound which is particularly irritating to horses.
Habitat
Horseweed grows in pastures, waste areas, along roadsides, and in cultivated fields. It is native to grasslands.

Management Options

Non-Chemical Management
  • Maintaining a healthy planting or turf area to provide competition will prevent weed establishment.
  • Cultivation (rototilling or hoeing) will effectively eliminate plants.
  • Mowing to prevent seed production is a very effective means of management. In lawns, mowing regularly at the proper height for the grass species may help minimize weed growth and invasion.
  • Apply organic mulches, such as bark, compost, grass clippings, straw, and other materials, in a layer from two to several inches thick for effective weed management.
Select non-chemical management options as your first choice!

Chemical Management

Apply according to label directions. Glyphosate products should be applied as spot treatments only! NOTE: Some ingredients listed here are only available in combination. Read the label carefully on combination products to make sure the product is suitable for your specific situation.NOTE: Some ingredients listed here are only available in combination. Read the label carefully on combination products to make sure the product is suitable for your specific situation.

Landscape areas
  • glyphosate
Turf areas
  • 2,4-D + MCPP + dicamba
Bare ground areas
  • glyphosate
Images
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Caption: Horseweed flowerheads
Photo by: T.W. Miller
Caption: Horseweed seedheads
Photo by: T.W. Miller
Caption: Horseweed
Photo by: R. Parker
Caption: Horseweed
Photo by: R. Parker
Caption: Horseweed flowers
Photo by: R. Parker