And you thought bin Laden was dead

The Osama bin Laden of weeds is on its way to a field near you. Called Palmer amaranth, the vicious weed has been the scourge of the southland for many years, and with climes up north warming up these days, it will soon be at least a mini-scourge in the Upper Midwest.

Agri-View Crop News describes Palmer amaranth as “a very problematic annual broadleaf weed.” It said recently that the weed, a problem for growers in southern portions of the country, and has now turned up in Wisconsin. Palmer amaranth is a “cousin” to other pigweed species found commonly in the Upper Midwest. But it harbors one terrible difference: it is resistant to glyphosate and ALS inhibitor herbicides. That, said Vince Davis, University of Wisconsin-Madison’s cropping weed scientist, “drastically limits control options.”

Normally such pigweeds, in the same family as waterhemp, are easily inhibited and quickly killed by herbicides using glyphosates, but Palmer amaranth is resistant and the herbicide usually works when pigweed plants are in the three-inch phase. Once Palmer gets to the six-inch phase it’s really hard to control. The particular problem with Palmer amaranth is that it tends to grow three to six inches daily. That leaves a narrow window for treatment, said Jeff Caldwell of

The big news is that this hempy (or ropey), thick weed is moving north rapidly after having been the scourge of the south for some years.

“Palmer amaranth is the Osama bin Laden of weeds,” said Dave Rahe, certified crop adviser with Soil-Right Consulting Services, Inc., Hillsboro, Ill. “As with other resistant pests, rotating chemical families and modes of action should be helpful.”

Palmer amaranth is in the top 10 “Bad Weeds” for 2012. Glyphosate resistance is something to watch out for with this weed, just like waterhemp. That’s part of what makes it so hard to control, experts agree.

Palmer’s resistance to glyphosates is problematic because the weed is so competitive and aggressive. It’s the most competitive of all pigweed species and it produces large quantities of seed. Vince Davis discovered that technically Palmer amaranth could be considered a native species in the Upper Midwest, but he noted that heretofore it has been “certainly very rare at best.” That is changing rapidly with warm-up.

Farmers should, Davis said, be diligent in late-season weed scouting, looking for pigweeds that escaped control in their soybean or corn fields this year and take extra time to correctly identify what type of pigweeds they are. Key identification points include: stems that lack hair, the flower heads are long and skinny and the flower heads are sharp (prickly) to the touch of the bare hand.

If you are fairly sure you have Palmer amaranth escapeing in production fields, you can e-mail David at vm [email protected] to set up the sending of samples for him to study.

In the meantime, be diligent, because producers in several northern states are starting to identify Mr. bin Laden in the fields. He needs to be stopped dead.

I’ll see ya.


An Iowa native, Peter Graham has been a rural newspaper editor for 39 years. He currently edits a twice-weekly paper in Western Iowa. You can contact him at (712) 642-2791 or [email protected]