By Pamela Smith
Crops Technology Editor
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. | 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) |
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 |
The survey also found the most common and the most troublesome weed can overlap in key crops.
| Crop/Ecosystem | Most Troublesome Weed | Most Common Weed |
| 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 |
| Pastures, rangelands, right of ways | Canada thistle | Canada thistle |
| Soybean | horseweed (marestail) | foxtail (giant, green, yellow) |
The 2015 survey data is available at http://wssa.net/…. For more information, visit www.wssa.net.
(AG/CZ)
© Copyright 2016 DTN/The Progressive Farmer. All rights reserved.