Palmer Amaranth Threat Grows in the Midwest

Tough weed associated with the South has migrated north, in a big way.

Published on: Dec 20, 2013

Consider the following: The most recent Stratus Glyphosate Resistance Tracking Study, which is conducted annually by Stratus Agri-Marketing, found that the total area of U.S. cropland infested with glyphosate-resistant weeds expanded to 61.2 million acres in 2012. This same study indicated the rate at which glyphosate-resistant weeds are spreading is also gaining momentum, marked by an increase of 25% in 2011 and an astonishing 51% gain in 2012.

The data highlighted above isn't all Midwest-oriented, but the information should nonetheless serve as a wake-up call for all growers — even those who aren't yet being negatively impacted by herbicide-resistant weeds.

Midwest ag experts frequently cite common waterhemp, common and giant ragweed, common lambsquarters, shattercane, and marestail as examples of weeds that have become resistant to glyphosate and/or ALS inhibitors. But another weed — one that has historically been a problem with cotton in the Southeast — is rapidly gaining a foothold in the Midwest, thus capturing the attention of many.

MONSTER IN YOUR FIELD: Standing tall in a cotton field, Palmer amaranth is a common site, but in 2014, Midwest growers may see more of this prolific, resistant weed. Fast, strategic action will be needed to stop the pest.
MONSTER IN YOUR FIELD: Standing tall in a cotton field, Palmer amaranth is a common site, but in 2014, Midwest growers may see more of this prolific, resistant weed. Fast, strategic action will be needed to stop the pest.

A product of the Sonoran Desert, Palmer amaranth is a fast-growing (up to 2 or 3 inches per day) pigweed that not only thrives in dry conditions, but is also tolerant of high temperatures and intense sunlight; and it has evolved and adapted to the point where it can do well in places as diverse as Louisiana and Michigan (and many points in between). More problematic, however, is the fact that it's developing a resistance to glyphosate, as well as other herbicides.

Unfortunately, the weed appears to be spreading northward at a rapid pace, much like waterhemp did in the 1990s. Besides most of the Southeastern states, cases of Palmer amaranth infestations have already been documented throughout the Midwest, including parts of Ohio, Michigan, Indiana, Illinois, Wisconsin, Nebraska, Kansas and Missouri.

Given this, there's genuine concern that it's only a matter of time before this resilient weed finds its way into even more of the Midwest's most productive crop acreage, which is why experts stress the importance of growers being diligent and utilizing comprehensive weed management plans and practices.

"When Palmer amaranth becomes established in Iowa and Illinois, like it has in Michigan and some other states, it will be a game-changer," warns University of Illinois weed specialist Aaron Hager. "It has already put people out of business."

Yontz writes from Urbandale, Iowa.

Palmer Amaranth Threat Grows in the Midwest