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Palmer pigweed forces southern farmers to make changes

By Janet Kubat Willette
jkubat@agrinews.com

Date Modified: 04/19/2013 3:11 PM

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NORTH MANKATO — Tennessee farmers thought Roundup was a white knight riding in to save them from ALS weed resistance. Instead, Roundup was a loan that's coming due with interest.

That's how University of Tennessee row crop weed specialist Larry Steckel described the situation in Tennessee soybean fields at a Weed Resistance and Grain Management Seminar held March 28 in North Mankato. The traveling seminar was also held in Mahnomen and Willmar.

Palmer pigweed has changed how farmers operate in Tennessee, he said. In summer 2011, farmers lost more soybean fields to Palmer pigweed than all previous years combined.

It's like a heart attack victim who suddenly has to make lifestyle changes.

"That's where we are in Tennessee," Steckel said. "We're having a pigweed heart attack and we're being forced to change."

The first glysophate resistant Palmer pigweed was identified in Macon County, Ga., in 2005, he said. Since 2008, Tennessee farmers have lost fields annually to the resistant weeds. They harvest with a Bush Hog instead of a combine.

Palmer pigweed has put several farmers out of business, Steckel said. It has a five-foot taproot, is a tremendous seed producer and has outstanding drought tolerance. There are male and female plants and the resistance gene is carried in the pollen. It is a cousin to waterhemp, which is native to the Midwest.

Palmer pigweed is native to the desert Southwest. It reproduces rapidly in 90-degree-plus heat. In a 180 acre soybean field, Steckel and a farmer lost a pickup that had been parked on a rise because the pigweed hid it from view.

Steckel normally doesn't count the number of calls he receives in one day, but he did on June 21, 2011. He received 80 phone calls that day. It dawned on him what a mess they were in.

Farmers had three options:

• Till up the field and replant.

• Let it be.

• Keep spraying.

The winner that year seemed to be tilling up and replanting. They got 25 bushels per acre.

In 2012, it seemed that Tennessee farmers turned the tide, he said. They sent chopping crews to the fields earlier, they put more corn in the rotation and invest more time and money to do overlapping residuals. Farmers have to manage for seed after corn is harvested in late July or early August, spending $15 to $20 per acre on weed control after harvest. Cover crops are coming into the rotation.

It's a new mindset, Steckel said.

Farmers who have land along the river bottoms have incorporated tillage into their rotation, including putting cultivators back into use.

Farmers are spraying a lot, overlaying one residual pre-emergence herbicide over the other. They are spraying $70 to $100 worth of herbicides per acre on soybeans and not getting the control Minnesota farmers are getting with glysophate. An additional $50,000 to $100,000 annually was spent on chopping crews who go in with hoes to chop or pull Palmer pigweed. If left in the field, it will reroot, so most crews now pull the pigweeds.

Steckel showed a photo of a hay wagon heaped full of Palmer pigweed and a dike of Palmer pigweed at a field edge.

Palmer pigweed is not just a problem in Tennessee, he said. In 2011, 30 percent of soybean fields in Tennessee and Mississippi had unacceptable control. In Arkansas, 60 percent of fields had unacceptable control. Three million acres in the three states suffered significant yield loss.

Palmer pigweed is what farmers talk about in small town diners in the south, Steckel said.

Using his experience in Tennessee, he estimates a weed resistance issue like Palmer pigweed would cost Minnesota farmers an additional $621.2 million annually.

Proactive resistance management is by far more economical than reactive management, Steckel said.

Growers in Tennessee would do anything they could to keep glysophate in play, he said.

The time in Minnesota is short, with giant ragweed and common waterhemp already resistant to glysophate.

"You're still on the front end of this, you can make a difference, you're not in the mess we're in where we're losing fields," Steckel said.

Farmers are going to have to go back to how they farmed in the 1980s and early 1990s, when a big part of raising top-yielding crops was weed control.

"I don't think there's going to be another Roundup," he said.