November 20, 2013
Palmer pigweed has a big reputation and most of it gained by being a royal pain in the backside for row crop growers from the Florida Panhandle to the Upper Neck of Virginia.
It may have a bigger reputation for problems in the Lower Southeast, but make no mistake, Palmer amaranth is a problem for row crop production anywhere it lives.
As farmers transition from harvesting this year’s crops to planning next year’s, there is time to re-think basic weed control strategies.
A big part of managing a problem is knowing what the problem entails. North Carolina State Weed Scientist Wes Everman says a good first step for farmers in dealing with Palmer pigweed is to be able to accurately identify it at the seedling stage and to differentiate it from smooth and redroot pigweed species.
Once Palmers get mature, few have any problem with identification. However, in the fall and early spring they are easily confused with redroot and smooth pigweed.
How important is knowing the enemy?
In the case of pigweed, more specifically Palmer amaranth, it can be the difference in being in or out of farming.
University of Georgia Weed Scientist Stanley Culpepper has been at the forefront of battling pigweed in general, but glyphosate resistant pigweed in particular for the better part of 10 years now. He has great respect for his foe.
Management systems for Palmer pigweed are effective but costly. Georgia cotton growers spend more than $100 million per year to manage Palmer amaranth, he says.
That’s just one crop and one state. Glyphosate resistant pigweed is now found in multiple states and in multiple crops in the Southeast.
Control not economically sustainable
“One hundred percent of all growers who have had success will tell you the same thing,” Culpepper says,
“I was successful in managing the plant, but I’m not economically sustainable. We’re spending $80, $90, $100 per acre to manage this one plant. We cannot keep doing that.”
Everman says, Palmer pigweed with resistance to glyphosate and active ingredients in other often-used herbicides can be a huge problem throughout most of the calendar year.
Growers unintentionally, but routinely, move Palmer pigweed seed around their farm and to neighboring farms on equipment, even on clothing.
Resistance can move considerable distances on pollen. And, it too can be moved via equipment and other means.
Not only are pigweed seed mobile, plants at all stages of growth are also tremendously resilient, the North Carolina State researcher says.
“It’s very common to see Palmer pigweed get knocked down in the harvesting process with corn or soybeans and the farmer thinks the problem is solved. In many cases, I’ve seen pigweed re-root, take-off quickly and be a big problem,” he adds.
“Even mowing doesn’t always have much effect on pigweed. In some cases, mowing may actually mask a later problem with Palmer amaranth.