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Marestail/horseweed (Conyza canandensis) is a biennial weed that can reach heights of 3 to 6 feet. Seeds germinate throughout spring and early summer; plants mature and set seed the same year. Late-season plants overwinter in the rosette stage. One plant may release 200,000 seeds that disperse easily by wind. 

Marestail growth habit (Videki, Doronicum Kft., growth habit.

(Photo: Robert Videki, Doronicum Kft.,

Marestail growth habit (Strang, UKY)Marestail growth habit.

(Photo: John Strang, University of Kentucky)

Marestail flowers (Harte, flowers.

(Photo: Mary Ellen (Mel) Harte,



  • Cultivate at renovation.
  • Apply pre-emergent herbicides to prevent seed germination.
  • Burn-down herbicides during seedling or rosette stages destroy young plants.
  • Glyphosate-resistant marestail is becoming more common.


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