Palmer amaranth has now been confirmed in more than 30 counties in Iowa, in both conventional farm operations and in native seed mixes for conservation purposes. Farmers, crop consultants and those interested are encouraged to attend meetings and field days sponsored by Iowa State University Extension to learn more about this new weed that has moved into Iowa over the past few years. The next Palmer amaranth identification workshop hosted by ISU Extension is Sept. 23 at the American Legion in Central City, Iowa at 9:30 a.m.

NEW WEED THREAT: Palmer amaranth is showing up in more fields in Iowa. “The misconception is that this problem is isolated and not within a farmer’s specific county," says ISU Extension agronomist Mike Witt. “Fact is, infestation of Palmer is statewide and more county identifications are likely to occur in the future.”

ISU field agronomist Meaghan Anderson says the one-hour workshop will update the situation with this weed. “With Palmer amaranth discoveries quickly increasing across the state this summer, proper identification is key to controlling infestations and preventing movement to crop fields,” she says.

Farmers and crop scouts should be watchful for high risk areas
This workshop will discuss new discoveries of Palmer amaranth across the state, key traits to differentiate the common amaranth species in Iowa from Palmer amaranth, and management of this weed in both crop and non-crop areas. “Farmers and crop scouts should be observing high-risk areas for Palmer amaranth, including areas with significant equipment movement, suspicious-looking waterhemp infestations, newly-seeded conservation plantings, and areas near animal agriculture or livestock operations,” says Anderson.  

This meeting is free and open to the public. The American Legion is located at 6 Central City Road in Central City, Iowa. For more information, please contact Meaghan Anderson at 319-337-2145 or [email protected].

This new weed in Iowa could cause significant yield loss in future
Palmer amaranth has been confirmed in both conventional farm operations and in native seed mixes for conservation purposes. ISU Extension field agronomist Mike Witt hosted four Palmer amaranth informational meetings the past two weeks in west central Iowa. The meetings were held between Sept. 14 and Sept. 22, and focused on identification, biology and management of Palmer amaranth in conservation plantings as well as in row crop conditions.

Palmer will likely be found and identified in more counties
“Palmer amaranth could cause significant yield losses in the future,” says Witt. “Identification and elimination of Palmer amaranth in conservation plantings early are some of the best steps in prevention.” The informational meetings put on by ISU Extension are one hour long and handouts about Palmer amaranth identification are provided. At the meetings farmers and others have the opportunity to learn about current Palmer issues, and learn how to develop management plans to reduce the likelihood of the weed spreading into crop fields.

“The misconception is that this problem is isolated and not within a farmer’s specific county," says Witt. “The fact is, the infestation of Palmer amaranth is statewide and more county identifications are likely to occur in the future.”

What’s the deal with cover crop seed and Palmer amaranth?
Most people are aware of Palmer amaranth seed contamination in native seed mixes. These findings have led to questions about whether cover crop seed might also be a source of Palmer amaranth. “We are not aware of any situations of cover crop seed used in Iowa being a source of Palmer amaranth, and have not heard of this situation in other Midwest states,” says ISU Extension weed management specialist Bob Hartzler.

“We feel the risk should be very small for two reasons,” adds Hartzler. “The first is that the majority of cover crop species grown in Iowa are winter annuals (e.g. cereal rye, oats), whereas Palmer amaranth is a summer annual. Because of this difference in life cycle, cover crop species are harvested when there would be no mature Palmer amaranth present to directly contaminate the crop seed. The second reason is that most winter annual cover crop seed planted in Iowa is produced in Iowa, South Dakota and North Dakota. None of these states currently have widespread Palmer amaranth (not considering the introduction of Palmer amaranth in conservation plantings this season), therefore reducing the likelihood of contamination.”

Cover crop seed can be the source of weed seed in some cases
There is no doubt that cover crop seed can be the source of weed seed. In most cases, the weed seed are winter annual species that are easily managed with tillage and/or herbicides. “We cannot rule out the possibility of cover crop seed being contaminated with Palmer amaranth seed,” says Hartzler. If cover crop seed did contain this problematic weed, it would likely be due to seed being present in machinery used to harvest or clean seed, rather than plants growing in the cover crop seed field. In this situation, the number of weed seed in the cover crop seed would be much lower than has been observed in conservation plantings across the state.

“To summarize, we are not aware of any cases where Palmer amaranth was introduced via seed of traditional cover crops,” notes Hartzler. “The risk of introducing this new species can be minimized by confirming that the source of the seed is from a state where Palmer amaranth is not widespread and purchasing certified seed. Since Palmer amaranth is not classified as a noxious weed in Iowa, Palmer amaranth seed is not restricted in certified seed, and its presence in the crop seed does not need to be listed. However, certified seed typically is produced under more stringent conditions, thus reducing the risk of contamination with weeds in general.”