Mark Loux gives a presentation at a Weed Resistance meeting.

Palmer amaranth gaining ground in Ohio

The Farm Science Review could be a great place to find out more about the Palmer amaranth that has been making plenty of ag headlines lately. This nightmare of an herbicide resistant weed threatens to change weed management as most farmers know it. They could be trading in their big sprayers for a hand hoeing crew.

Ohio State University Extension weed control specialist Mark Loux is increasingly concerned about this monster weed in Ohio.

“There appears to be somewhat of an epicenter of new Palmer amaranth infestations in an area southwest of Columbus, bordered roughly by Midway on the north and Washington Courthouse on the south. There is a dairy in the area that has been using cottonseed products for feed and a local grower has been transporting these products to the dairy from somewhere in the south,” Loux said in a recent CORN Newsletter. “There are Palmer amaranth plants in a number of fields in the area and also on the grounds of the dairy. One grower contacted us after finding it in his field, and has since been busy digging out and removing plants. If you farm in this area, be sure to take some time to scout fields and roadsides now for Palmer amaranth and take appropriate action as necessary. Palmer amaranth is a prohibited noxious weed in Ohio.”

Thus far, it appears that the plants have not gone to seed, which is good.

“The Palmer amaranth plants we have found so far do not appear to have formed mature seed yet, which would be indicated by the presence of small black seeds. We’re not sure why but one hypothesis is that the residual from preemergence herbicides prevented the early flushes of Palmer amaranth, and the later-emerging plants are still reaching maturity,” Loux said. “This means that there is still time to dig up or chop down plants, and ideally also remove them from the field. Once mature seed has formed, the strategy changes from plant removal to isolation and remediation of infestations.”

There are a number of resources available to learn more about this daunting weed. The OSU weed science website ( has information on Palmer amaranth, including a short video on identification and a new 11-minute video that explains the risk from this weed, Loux said. The Farm Science Review will offer ample opportunities to meet with many OSU and Purdue Extension specialists to learn more about Palmer amaranth, as representatives from both universities will be there through the entire show.

In addition, Purdue University has developed a new publication on Palmer amaranth. It is now available for free through Purdue Extension’s The Education Store.

“Palmer Amaranth Biology, Identification and Management” was created by Purdue Extension weed scientists Bill Johnson and Travis Legleiter in an effort to curb the weed’s expansion to the northern U.S. The 11-page publication can be downloaded at, where it can be found by searching for “WS-51.” Print copies can be ordered for $2.10 each, plus shipping and handling.

“We’re very concerned about the competiveness, the seed production and the impact Palmer amaranth can have on Midwest crops,” Johnson said. “We feel this is a weed we really need to get on top of before it becomes very widespread.

“It’s arguably the worst weed problem to hit agronomic crops in the southern United States. We’ve watched cotton fields being mowed down before harvest because of Palmer amaranth.”

Those who find plants that could be Palmer amaranth need to contact Ohio State University Extension to confirm identification, and at that point Extension specialists can also offer more guidance for management of new infestations.


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