Palmer up and growing

Palmer amaranth is a new weed in Iowa, having moved up from the southern U.S. into the northern Corn Belt in recent years. It’s a hard-to-control weed that looks a lot like its “cousin” common waterhemp, especially when the weeds are small.

Palmer up and growing

Palmer amaranth is a new weed in Iowa, having moved up from the southern U.S. into the northern Corn Belt in recent years. It’s a hard-to-control weed that looks a lot like its “cousin” common waterhemp, especially when the weeds are small.

The first confirmed Palmer amaranth infestations in Iowa were found in late 2013. Infestations have been found in five Iowa counties so far, “but we suspect there are more unknown infestations than known,” says Iowa State University Extension weed management specialist Bob Hartzler.

Virgil Schmitt, an ISU Extension field agronomist in southeast Iowa, and Hartzler visited an infestation in Muscatine County on May 9. There was an abundance of amaranthus seedlings present in the area that was infested with Palmer amaranth last fall. “We are fairly confident these seedlings were Palmer amaranth because there was little or no waterhemp, or other pigweed species, present in the field last fall,” says Hartzler. “However, I’m not convinced it is possible to distinguish the two species while they are in the seedling stage.”

While plants are in the vegetative stage, the long petioles on Palmer amaranth are probably the best trait to differentiate Palmer amaranth and waterhemp, says Hartzler. Palmer amaranth leaves frequently are wider in relation to their length compared to waterhemp. Palmer amaranth also tends to have a “bushier” growth habit, whereas waterhemp is leggy and has an open canopy. Another characteristic of Palmer is its very rapid growth rate.

Key Points

Watch your fields closely this spring to manage the spread of Palmer amaranth.

This difficult-to-control weed was first confirmed in Iowa in 2013.

Early detection of this weed is important in order to control its spread.

Can this weed be stopped?

“A poster describing the two weeds is available for downloading on the ISU Weed Science website www.weeds.iastate.edu, and we have a limited supply of printed copies,” Hartzler adds. “However, there are a number of other articles on the ISU weed science website providing information about identification and management of Palmer amaranth.”

The simplest way to manage a weed is to prevent it from getting established. “While it is unlikely that all of the current Palmer amaranth infestations will be eradicated, the rate that Palmer amaranth spreads across the state can be reduced,” says Hartzler. “Early detection of new infestations is critical. Unfortunately, the similarities between Palmer amaranth and waterhemp complicate this process.”

He is advising farmers and crop consultants to closely monitor fields for any unusual looking “pigweeds.” It is relatively easy to differentiate the two species once they begin to flower. “We at ISU would appreciate being contacted if any fields are found with suspected Palmer amaranth in Iowa,” adds Hartzler. He can be reached at [email protected] or 515-294-1923.

Source: Iowa State University

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weed spotted: A group of Palmer amaranth seedlings was found in an Iowa field this spring.

This article published in the June, 2014 edition of WALLACES FARMER.

All rights reserved. Copyright Farm Progress Cos. 2014.

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