Iowa farmers continue to battle invasive plant species in the field

University of Delaware Extension Specialist Mark VanGessel holds an uprooted Palmer amaranth plant. (University of Delaware Carvel REC/Flickr)
University of Delaware Extension Specialist Mark VanGessel holds an uprooted Palmer amaranth plant. (University of Delaware Carvel REC/Flickr)

Nick Fetty | January 8, 2015

Palmer amaranth, waterhemp, and other nuisance plant species continue to be growing problems for farmers in Iowa and neighboring states.

Weather and environmental conditions are two factors that have contributed to this problem. Droughts in 2013 forced farmers to delay application of herbicides and cool, wet conditions in 2014 further exacerbated the situation with problem weeds.

Waterhemp is “one of the most common weeds with which Midwest farmers must contend” according to data from the Purdue University Extension. Mike Owen – an Iowa State University Extension weed specialist – estimates that 85 percent of Iowa soy bean fields have waterhemp resistance.

In addition to waterhemp, Palmer amaranth has also caused issues for Iowa farmers. Instances of this bothersome weed have been reported in Page, Fremont and Harrison counties in the southwest part of the state in addition to Lee and Muscatine counties in the southeast. Owen said there are likely more unreported cases of Palmer amaranth in Iowa since it is prevalent in nearby states such as Illinois, Kansas, Missouri, and Nebraska.

Robert Hartzler – an Iowa State University Extension weed management specialist – does not believe that Palmer amaranth will be as devastating in Iowa as it has been in southern states. These weeds were largely unheard of prior to the 1980s when weed management practices changed.

Waterhemp and Palmer amaranth are similar in appearance and can often be difficult to differentiate.

On the Radio: Superweed spreads into Iowa fields

Palmer amaranth, an aggressive superweed found in five southern Iowa counties. (University of Delaware Carvel REC/Flickr
Palmer amaranth, an aggressive plant found in five southern Iowa counties so far. (University of Delaware Carvel REC/Flickr

This week’s On the Radio segment looks at palmer amaranth, an invasive superweed that has recently been spotted in five Iowa counties. Listen to the audio below, or continue reading for the transcript.

Transcript: Superweed

A new superweed that can now be found in five southern Iowa border counties may pose a serious threat to Iowa farmers.

This is the Iowa Environmental Focus.

Palmer amaranth is an extremely aggressive plant that can grow up to seven feet tall in a matter of weeks. It has only reached Iowa in the past year, but it has been seen in Southern states since as early as 2005.

Farmers who have dealt with the weed report that it has significantly reduced their crop yield. The weed’s rapid growth and superior size allow it to spread quickly and outcompete other plants.

Research is in progress to determine if Palmer amaranth may be herbicide resistant. If so, the plant would join the ranks of 20 other Iowa weeds that are unaffected by most weedkillers.

Herbicide resistant weeds force farmers to use stronger chemicals and increased tillage to preserve their crops, tactics which cause concern among environmental experts.

For more information about Palmer amaranth, visit

From the UI Center for Global and Regional Environmental Research, I’m Jerry Schnoor.