Palmer amaranth: Find it, stop it

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(University of Delaware/Mark VanGessel photo)Palmer amaranth is an aggressive and destructive weed. The white mark on the leaves in the forefront and on left are similar to a thumbprint, and is distinctive to palmer amaranth, but not every plant will show this characteristic.

SALEM, Ohio — Farmers, if you think marestail is a nuisance, then you don’t even want to deal with an eruption of Palmer amaranth in your fields.

Weed experts call Palmer amaranth a “super weed” that could be a nightmare if found on your farm.

Invasive

Palmer amaranth, a weed from the Pigweed species, is a growing problem in the South because is glyphosate-resistant. If it shows up on your farm, you can expect a loss in the crop yield and a permanent increase in the cost of herbicide programs.

It can spread quickly once it emerges, because a female plant can produce between 100,000 and 500,000 seeds. In addition, the plant can stand up to 7 feet tall, and can grow as much as 3 inches per day.

The weed can emerge any time between April and August.

Stop Palmer amaranth from spreading

  • Plant a cereal rye cover crop. The rye cover crop can provide a mulch that will suppress Palmer amaranth emergence.
  • Hire hand weeding crews to remove Palmer amaranth. It is important that Palmer amaranth should be pulled and taken out of the field and composted or burned. Plants that are laid on the soil in the field will reroot and continue to grow and produce viable seed.
  • Producers are also urged to rotate crop and use deep tillage including the moldboard plow. By using deep tillage, the Palmer amaranth seed will fall below its preferred emergence depth. Researchers at Purdue Extension found that it will not provide complete control, but will reduce the number of seeds that can emerge from the top one inch of soil.
  • Producers are also reminded to check ditches and field borders. The fear is the weed can spread into a field through pollen and seed.

Reduced yields

According to Extension specialists in Georgia and Arkansas, Palmer amaranth has invaded over 750,000 acres of cotton and other row crops in Arkansas and over 1 million acres in Georgia. It has reduced yields by up to 75 percent in some fields where it has been found.

Populations in the South have developed resistance to 14 herbicides (fomesafen, Cobra, etc), and appear to be developing resistance to glufosinate (Liberty, Cheetah, Interline).

Pennsylvania and Ohio

Now it has been found in Ohio and Pennsylvania, too.

Prior to 2015, there were only a couple of outbreaks of Palmer amaranth in Ohio, according to Dr. Mark Loux, Ohio State University horticulture and crop scientist.

Palmer amaranth was first found in Pennsylvania in 2013 and has quickly spread. The “super weed” has been found in alfalfa, corn and soybean fields in both states.

Palmer amaranth has been found in 11 Ohio counties, according to OSU Extension — Williams, Putnam, Sandusky, Wayne, Lorain, Highland, Ross, Scioto, Madison, Fayette and Mahoning. In Pennsylvania, Palmer amaranth has been identified in Lawrence, Centre, Blair, Bedford, Somerset, Cumberland, Franklin, Dauphin, Lebanon, Berks, Lehigh, Montgomery and Chester counties. According to Penn State Extension, between 12 and 15 sites were found in Lancaster County alone by the end of 2015.

According to Loux, most counties only have a few populations of Palmer amaranth.

No pattern

Loux said there isn’t any real pattern to the distribution of counties where Palmer has been found. He said Palmer seed entered the state via contaminated CREP or wildlife seed that comes from out West, and via the cotton feed products that are shipped from the South and used in animal operations.

Palmer is more widespread in an area near two dairies along the Madison-Fayette county line north of Jeffersonville, Ohio.

New infestations

There were new infestations in 2015 in northeast Ohio counties, including Lorain, Mahoning, and Wayne, presumably as a result of Palmer seed in cotton-based feed products.

In Mahoning County, the grower had zero Palmer amaranth in 2014. Then last winter, the grower purchased one load of cottonseed feed product from a local dealer last winter. The grower fed the cottonseed in his ration, then spread his herd’s manure on fields in late winter and early in 2015.

The result was dense Palmer amaranth infestations in 2015 in these fields, and the farmer is still trying to control the outbreak with glyphosate.

Researchers are also concerned that the seed could have been spread even further by the combine used to take off the crop by a custom harvester.

Palmer Amaranth
Palmer amaranth is an invasive weed that has made its way into Ohio and Pennsylvania.

Identification

So what’s it look like? When identifying Palmer amaranth, look for a smooth stem and some singular plants have a single hair at the leaf tip. Immature Palmer amaranth tends to have a poinsettia-like appearance. There is also a white thumbprint found in the middle of the leaves.

If you do suspect Palmer amaranth in your field, call OSU Extension and contact a weed specialist to confirm it has been located.

Eradication

Once it is found, however, the hard work begins, because it is glyphosate resistant. Purdue Extension experts offer some ways on stopping the seed from spreading, and one way is to plant a cereal rye cover crop, which can provide a mulch that will suppress Palmer amaranth emergence.

In some Indiana soybean fields, producers have resorted to hiring hand weeding crews to remove Palmer amaranth.

It is important to note that weeds should be pulled and taken out of the field and composted or burned. Plants that are laid on the soil in the field will reroot and continue to grow and produce viable seed.

Producers are also urged to rotate crop and use deep tillage, including the moldboard plow. By using deep tillage, the Palmer amaranth seed will fall below its preferred emergency depth. Researchers at Purdue Extension found that it will not provide complete control, but will reduce the number of seeds that can emerge from the top inch of soil.

Producers are also reminded to check ditches and borders. The fear is the weed can spread into a field through pollen and seed.

Know what Palmer amaranth looks like and if there is any in the neighborhood.

  • When purchasing used equipment, know where it has been. Avoid buying combines that come from Palmer-infested areas.
  • When purchasing used equipment, know where it has been. Avoid buying combines that come from Palmer-infested areas.
  • Scout recently seeded CREP, wildlife, and similar areas for the presence of Palmer. For any intended seedings of this type, ODA will test seed lots for the presence of Palmer seed at no charge. They must pick it up from your operation (do not mail or drop off). Contact ODA for more information, 614-728-6410.
  • Avoid use of cotton feed products that might contain Palmer amaranth seed; check with feed supplier for more information. When using manure from an animal operation, know whether they are using cotton feed products.
  • Include residual herbicides in corn and soybean programs to control the early-emerging Palmer amaranth plants.
  • If Palmer plants are evident at the time of postemergence treatment, modify the herbicide program appropriately.
  • Scout fields starting in mid-July for the presence of Palmer that escaped herbicide programs. Get help with identification if in doubt.
  • Plants without mature seed (black) should be pulled out (uprooted) or cut off just below soil and removed from field, and then burned or buried at least a foot deep or composted. Plants with mature seed should be bagged and removed from field.
  • Do not run the combine through Palmer patches that are discovered during harvesting.
  • Resources for additional information on management of established populations: http://u.osu.edu/osuweeds/; http://takeactiononweeds.com.

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4 COMMENTS

  1. I believe we have it on our farm here in Beaver Count, Brighton Township, PA. Is PA tracking this week, and if so, where do we report it? Thanks.

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