Pigweed Worst Weed

Look What's Living in the Weed Patch

Pam Smith
By  Pam Smith , Crops Technology Editor
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It's a jungle in this northern Illinois soybean field. Palmer amaranth, waterhemp, foxtail combine to take a toll on yield. (DTN photo by Pamela Smith)

DECATUR, Ill. (DTN) -- Palmer amaranth is a bully. Southern farmers have been known to compare the weed to the boll weevil in terms of cost and destruction. Now it has the dubious distinction of being named the most troublesome weed in the United States.

A new Weed Science Society of America (WSSA) survey ranks Palmer amaranth, also known as Palmer pigweed, at the top of the list of weed worries. Weeds in the Galium genus (cleavers, catchweed bedstraw and false cleavers) ranked as the most troublesome in Canada.

"We certainly weren't surprised to find Palmer amaranth at the top of the U.S. list," said Lee Van Wychen, Ph.D., science policy director for WSSA, in a news release. "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."

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.

Herbicide-resistant Palmer amaranth has been documented in 26 U.S. states, according to the International Survey of Herbicide Resistant Weeds. Weed scientists have been increasingly concerned as the desert plant can now be found as far north as Michigan. Resistance to multiple herbicide sites of action is also becoming more frequent.

The WSSA lists below are based on an aggregation of survey responses, which mentioned more than 650 weeds at least once.

Most Troublesome Weeds, U.S.

1. Palmer amaranth

2. morningglory (ivyleaf, pitted, tall, sharppod)

3. common lambsquarters

4. waterhemp (common, tall)

5. horseweed (marestail)

Most Common Weeds, U.S.

1. foxtail (giant, green, yellow)

2. common lambsquarters

3. crabgrass (large, smooth)

4. Palmer amaranth

5. Morningglory (ivyleaf, pitted, tall, sharppod)

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

1. Galium (cleavers, catchweed bedstraw, false cleavers)

2. wild oat

3. Canada thistle

4. kochia

5. wild buckwheat

Most Common Weeds, Canada

1. wild buckwheat

2. wild oat

3. pigweed (redroot, smooth)

4. foxtails (green, yellow, giant)

5. common lambsquarters

The survey also found the most common and the most troublesome weed can overlap in key crops.

Crop Ecosystem: Cereal grains, spring

Most Troublesome Weed: wild oat

Most Common Weed: wild oat

Crop Ecosystem: Cereal grains, winter

Most Troublesome Weed: downy brome/cheatgrass

Most Common Weed: downy brome/cheatgrass

Crop Ecosystem: Corn

Most Troublesome Weed: waterhemp (common, tall)

Most Common Weed: foxtail (giant, green, yellow)

Crop Ecosystem: Cotton

Most Troublesome Weed: Palmer amaranth

Most Common Weed: Palmer amaranth

Crop Ecosystem: Pastures, rangelands, right of ways

Most Troublesome Weed: Canada thistle

Most Common Weed: Canada thistle

Crop/Ecosystem: Soybean

Most Troublesome Weed: Horseweed (marestail)

Most Common Weed: foxtail (giant, green, yellow)

The 2015 survey data is available at http://wssa.net/…. For more information, visit www.wssa.net.

Pam Smith can be reached at pam.smith@dtn.com


Pam Smith