Home News WSSA ranks Palmer amaranth as most troublesome weed in U.S.

WSSA ranks Palmer amaranth as most troublesome weed in U.S.

Photo courtesy of the United Soybean Board (USB)

by Ben Nuelle

A Weed Science Society of America survey says Palmer amaranth is the most troublesome weed in the U.S. But how big of a problem is it in Iowa?

The WSSA released the survey results Tuesday.

Iowa State University Weed Specialist Mike Owen says Palmer amaranth certainly has gained considerable notoriety in the South and the Mississippi delta and even in southern Illinois and Missouri as being a major weed problem.

“I would say however that a majority of the corn and soybean acres in the upper Midwest which are the majority of corn and soybean production in the United States in fact we have greater issues with the near relative of Palmer amaranth, Water hemp.”

Owen says farmers can use more than herbicides to combat Water hemp.

“Well I think we have to consider what we have been doing and certainly the evolution of herbicide resistance by the way which is not synonymous with Glyphosate resistance. We have considerable infestations of Water hemp in Iowa that are resistant to herbicides other than Glyphosate but I think we need to go to the basics and consider the integration of weed management strategies beyond just using another herbicide.”

Hundreds of weed scientists, extension agents and practitioners across 49 U.S. states, Puerto Rico and eight Canadian provinces participated in the 2015 WSSA survey. They provided input on both the most common weeds (those most frequently seen) and the most troublesome weeds (those most difficult to control) in 26 different cropping systems and natural areas.  The lists below are based on an aggregation of their responses, which mentioned more than 650 weeds at least once.


WSSA Survey Results below:

Most Troublesome Weeds, U.S. Most Common Weeds, U.S.
1. Palmer amaranth 1. foxtail (giant, green, yellow)
2. morningglory (ivyleaf, pitted, tall, sharppod) 2. common lambsquarters
3. common lambsquarters 3. crabgrass (large, smooth)
4. waterhemp (common, tall) 4. Palmer amaranth
5. horseweed (marestail) 5. morningglory (ivyleaf, pitted, tall, sharppod)

Three weeds – common lambsquarters, morningglory species and Palmer amaranth – appear on both lists above.

For Canada, weed species in the Alberta, Saskatchewan and Manitoba prairies tended to dominate the survey.  Wild buckwheat and wild oat appeared on both the “most troublesome” and “most common” lists.


Most Troublesome Weeds, Canada Most Common Weeds, Canada
1. Galium (cleavers, catchweed bedstraw, false cleavers) 1. wild buckwheat
2. wild oat 2. wild oat
3. Canada thistle 3. pigweed (redroot, smooth)
4. kochia 4. foxtails (green, yellow, giant)
5. wild buckwheat 5. common lambsquarters

Among the other significant findings from the 2015 WSSA survey were the most troublesome and the most common weeds in several key crops and ecosystems across the U.S. and Canada:


Crop/Ecosystem Most Troublesome Weed Most Common Weed
Aquatic systems hydrilla watermilfoil (Eurasian, hybrid)
Cereal grains, spring wild oat wild oat
Cereal grains, winter downy brome/cheatgrass downy brome/cheatgrass
Corn waterhemp (common, tall) foxtail (giant, green, yellow)
Cotton Palmer amaranth Palmer amaranth
Parks, wildlife refuges Canada thistle downy brome/cheatgrass
Forestry Japanese stiltgrass (Mary’s-grass, Nepalese browntop) Japanese stiltgrass (Mary’s-grass, Nepalese browntop)
Fruit and nut crops eastern poison-ivy red sorrel
Pastures, rangelands, right of ways Canada thistle Canada thistle
Soybean horseweed (marestail) foxtail (giant, green, yellow)
Turf annual bluegrass crabgrass (large, smooth)
Vegetables nutsedge (yellow, purple) common lambsquarters


The 2015 survey data is available at http://wssa.net/wssa/weed/surveys. Scientific names for the weeds above are available in the WSSA composite list of weeds at http://wssa.net/wssa/weed/composite-list-of-weeds.

WSSA plans to conduct its weed survey annually, with a three-year rotation of different weed habitats. The 2016 survey focuses on weeds in broadleaf crops, fruits and vegetables.  The 2017 survey will focus on weeds in grass crops, pastureland and turf, while the 2018 survey will focus on weeds in aquatic environments, natural areas and other non-crop settings.