U.S. soybean farmers know Palmer amaranth by different names, including pigweed and carelessweed.

By any name, however, this weed is highly competitive with soybeans in many areas of the country.

Palmer amaranth presents a threat to soybean farmers for many reasons, including:

• Its growth rate can reach more than one inch per day;

• Each plant can produce 250,000 to 1.5 million seeds each year;

• It can grow up to eight feet tall;

• And the stalks are very thick — about the width of a baseball bat.

In addition to these factors, recent confirmations of glyphosate resistance in this weed make controlling it more of a challenge.

As a result, soybean farmers and weed scientists must take a second look at control methods.

Reports of resistance first came in 2005 from some southern U.S. states. Since that time, weed scientists have continued to verify resistance not only in the South but in other states as well. If farmers have not noticed resistance in Palmer amaranth yet, it may only be a matter of time before they do.

Ken Smith, Extension weed scientist at the University of Arkansas Division of Agriculture, and his team urge farmers in other states to take notice of this prolific weed and plan now for future control measures.

Smith says controlling Palmer amaranth includes proper management techniques, such as:

• Starting with a clean field;

• Overlapping residual herbicides;

• And managing the soil seed bank.

Learn more at http://www.unitedsoybean.org/.