A weed that's been a nightmare for farmers to control in the southern U.S., Palmer amaranth, was first identified in a field in Iowa last August. What's the update on this weed in Iowa? Has it been found in other counties in the state? Iowa State University Extension weed specialist Bob Hartzler says as of February 20, there are known infestations of Palmer amaranth in five Iowa counties: Davis, Fremont, Harrison, Muscatine and Page.

"It is likely new infestations will be discovered," he says. "Knowing how to identify Palmer amaranth is the best tool to limit its spread."

PALMER AMARANTH: This broadleaf weed is closely related to other pigweed species such as waterhemp, smooth pigweed and redroot pigweed.

Palmer amaranth is native to the Southwest United States, but has been expanding its range for at least 50 years. "Most recently it has moved into the Midwest and has been reported in all Corn Belt states except for Minnesota and the Dakotas," notes Hartzler. "While there are five counties in Iowa with known infestations, it's likely there are additional infestations that have not been brought to our attention."

It is likely there are other infestations of Palmer in Iowa
The first confirmed finding of Palmer amaranth in Iowa was near Modale in Harrison County in August 2013. It appeared the Palmer amaranth was introduced in two fields where sludge has been repeatedly applied due to the soils being unsuitable for crop production. The sludge was imported from Nebraska, but it does not appear to be a likely source of weed seed, says Hartzler.

"We suspect the seed came as a hitchhiker on trucks bringing the sludge into Iowa," he explains. "It is likely the Palmer amaranth has been present at this site for several years, and it has spread to several adjacent fields. A second, much smaller infestation was later found approximately 40 miles from the initial site. While it probably is too late to eradicate the Palmer at the Modale site, significant efforts are being made to contain the infestation."

~~~PAGE_BREAK_HERE~~~

Muscatine County along Iowa's eastern edge was the next confirmed Palmer amaranth infestation. The field is on a sandy soil in the flood plain of the Cedar River. The likely source for Palmer amaranth at this site was swine feed, says Hartzler. The infestation appears to be limited to a single field and the adjacent ground. The farmer is taking the problem seriously and there is a good likelihood of eradicating the weed from this location.

Two counties in the southwest corner of Iowa—Fremont and Page—were the next findings, both adjacent to commercial grain elevators. The likely source of Palmer amaranth at these sites is grain trucks that have been to areas in Nebraska or Missouri that have Palmer amaranth infestations.

The final report of Palmer amaranth in Iowa was received late in 2013 from a farmer in Davis County in southeast Iowa. He reported that the farm brings in cotton seed as a feed supplement for a cattle operation and believes this is where the Palmer amaranth originated.

Contact ISU weed or crop specialists if you find Palmer in your field
"I have not been to the last three infestations, I haven't personally seen them," says Hartzler. "Therefore, I'm not aware of the extent of the infestations or the efforts being made to eradicate or contain the Palmer amaranth at these locations."

Due to long-distance movement of equipment, grain and other agricultural materials, it is inevitable that new infestations of Palmer amaranth will be discovered in Iowa, he says. Knowing how to identify Palmer amaranth and keeping an eye out for 'odd pigweeds' is the best tool to limit the rate of spread of Palmer amaranth. "We appreciate being made aware of any new findings of Palmer amaranth in the state," he adds. You can contact Hartzler at [email protected]. Visit the ISU weed science website for more information.

"We encourage continued vigilance for the presence of this weed and will appreciate being contacted when suspect populations are found," says Hartzler. "Remember, the simplest and most cost-efficient manner of managing Palmer amaranth, or any new weed species is early detection and eradication before a permanent infestation is established. If found early, plants can be removed from the field before seed production establishes a permanent seed bank and persistent problem."