Horseweed (marestail)

Photo

Images: Horseweed seedling (above), and mature horseweed plant (below; credit Penn State University)

Horseweed (also called marestail) is of rising concern in many states due to its rapidly spreading herbicide resistant populations. It is a winter annual, and its seeds are wind-dispersed. It should be controlled when seedlings are small in order for herbicide applications to be effective, and not allowed to go to seed.

Resistant populations:

  • Group 2 (ALS)
  • Group 9 (glyphosate)
  • Group 2 + Group 9
  • Group 22
  • Group 9 + 22

Locations of resistant populations:

Arkansas, Delaware, Illinois, Iowa, Maryland, Mississippi, Missouri, Nebraska, North Carolina, Pennsylvania, Tennessee, Virginia

Resources:

Biology and Management of Horseweed – Part of the Glyphosate, Weeds, and Crops Series

Herbicide recommendations for horseweed in no-till soy – Iowa State University