The Worst Weeds, Ranked

What’s the most troublesome weed in the U.S., according to hundreds of weed scientists and Extension agents? The survey, conducted by the Weed Science Society of America (WSSA) has crowned Palmer amaranth the worst of the worst.

“We certainly weren’t surprised to find Palmer amaranth at the top of the U.S. list,” says Lee Van Wychen, science policy director at WSSA. “This weed can have a devastating impact on crop yields. Its stems are tough enough to damage rugged farm equipment, and it is extremely prolific. A single Palmer amaranth plant can produce as many as a million seeds during a growing season.”

The WSSA survey asked participants to list weeds most frequently seen, as well as species that are the most difficult to control. Here are the top five responses in each category.


Canadian weed scientists were also surveyed. In Canada, the “worst weed” landscape looks quite a bit different. The top five most troublesome weeds listed are gallium, wild oat, Canada thistle, kochia and wild buckwheat.

A 2015 Farm Journal Pulse poll revealed more farmers felt waterhemp was enemy No. 1 (35%), followed by marestail (19%), ragweed (14%), palmer amaranth (13%), “other” (11%) and grass species (8%). A 2013 Pulse poll showed similar results.


Worried about weed control this upcoming crop season? Try these AgWeb resources on for size.

  • AgWeb Online Field Guide – learn more about 74 economically significant weed species.
  • Weed Identification Guide – work through leaf, stem, root and flower characteristics to determine which weed you’re up against.
  • Most Wanted: Weeds Edition – learn more about Palmer amaranth, marestail and other top weed “criminals.”
  • Estimate Loss Calculator – this interactive tool lets farmers figure out the economic toll weeds are taking in their fields.
  • Blasting Weeds Into Oblivion – need some catharsis? Read about this “true grit” tale of weed scientists who turned compressed air and organic grit into a deadly weed-killing sandblaster. 

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