Missouri Cotton Farmers Use Old Tactics to Fight a New Battle against Pigweed

February 10, 2012 06:32 AM
Missouri Cotton Farmers Use Old Tactics to Fight a New Battle against Pigweed


The following story was written by a University of Missouri student as part of the 2011 Sonja Hillgren/Farm Journal Ag Journalism Field Reporting Institute. Learn more.

By Katie Alaimo
PORTAGEVILLE, Mo. — As a cool autumn night settled on the Missouri Bootheel region, painting the sky with shades of violet and ushering in the first days of October, two slow-moving giants turned on their lights in the distance as they lumbered back and forth through a sea of white.

This steady procession of machine pickers gathering up their bounty of fluffy white cotton bolls revealed little of the daily challenges farmers contend with in preparation for these early days of harvest. Nor of the time, money and effort spent confronting the relatively new enemy of herbicide-resistant Palmer pigweed. 

Resistant Palmer pigweed first reared its head here in 2008 and has since posed a serious threat to the financial success of Missouri cotton farms, experts say. To keep fields clean, farmers are forced to boost control tactics in a costly battle depending on repeated use of expensive herbicides, field labor, extra tillage and crop rotation.

"This is the number one problem for the Mid-South, whether it’s in cotton, corn or soy," said Jason Weirich, assistant professor of plant sciences for the University of Missouri Delta Research Center, in Portageville.
sprayer cotton

A John Deere Hi-Cycle sprayer rolls through a cotton field near Senath, Mo. Before Palmer pigweed developed a resistance to glyphosate, fields required only two or three applications of Roundup on the Hi-Cyclers. Farmers now find it necessary to make multiple trips over their fields throughout the season using a variety of herbicides. Photo: Katie Alaimo

Nature Adapts. Missouri’s cotton farms are some of the state’s best-kept secrets, but the 325,000 acres sprawling across the region are evidence of the industry’s success, due in large part to the development of Monsanto Co.’s genetically modified Roundup Ready cotton seed. This miracle of modern science enabled farmers to coat entire fields with the herbicide glyphosate, commercially known as Roundup, without risking crop damage. Weeds died as cotton thrived. 

But repeated exposure to a single, powerful herbicide can bring about resistance within previously susceptible weeds. Gradually, Darwin’s theory of natural selection is played out as adapted weeds reproduce to replace their non-resistant predecessors.

"It’s called selection pressure," Weirich said. "The plant evolves, if you will. It can rapidly metabolize the herbicide."

pigweed cotton
Palmer pigweed towers over soybean plants near a cotton field in Portageville, Mo. The weeds can grow taller than corn stalks, with thick bases that present a formidable challenge to farmers in the Missouri Bootheel. Photo: Katie Alaimo
Palmer pigweed has proven itself particularly resilient.

Pigweed has separate male and female plants. Consequently, pollen from the male plant can travel long distances through the air to fertilize female flowers, contaminating many fields at once. A single plant can then produce up to two million seeds, making eradication nearly impossible.

In the past, technology has always been ready to confront the new generation of herbicide-tolerant weeds. For example, when the common cocklebur developed an herbicide resistance, Roundup Ready cotton was available for production.

Currently no new variety of herbicide-resistant cotton has been developed. Instead, extension agents like Weirich believe the solution will come with a change of mindset among farmers toward weed control. 

The solution cannot come from a single tool as it has in the past with glyphosate, but through a combination of many tools — residual herbicides with contact herbicides and hooded sprayers, Weirich said. 

"You can’t build a house with just a hammer," he said.

Humans Adapt. On an early October morning at Jones and Abmeyer Farms of Senath, Mo., all is quiet save for the crunch of gravel beneath heavy boots, a calm before the flurry of activity that will commence with harvest. 

Owners Paul Jones and Ron Abmeyer have been farming cotton for 11 years and at 1,800 acres consider themselves a small- to medium-size operation. Since the arrival of Roundup-resistant pigweed Abmeyer and Jones have adapted their control program in response to the evolving landscape, chiefly with the addition of residual herbicides. 

After the field has been plowed Abmeyer and Jones apply a weed-killer cocktail, beginning mid-March with treatments of Clarity, FirstShot and STRUT. The process continues through the summer until August or September with pre-emergence Cotoran and Warrant, swapping in Ignite where pigweed is most severe. Jones and Abmeyer can spend up to $50 an acre on herbicides alone. 

Once considered a silver bullet, Roundup needed only one or two applications on a Hi-Cycle sprayer to cut weed populations. The influx of resistant pigweed now requires farmers to make several trips through the field using formerly outdated hooded sprayers that cover only 12 rows at a time and can knock fruit off higher plants.

weeds hoe cotton
Lewis Rone on his farm in Portageville, Mo., compares two hand hoes used to chop cotton. Rone said the homemade hoe (left) was sturdier than the store-bought (right) one, which broke when one of his field crew members attacked a pigweed that had grown too big. Photo: Katie Alaimo
Lewis Rone, who farms corn and cotton in Portageville, said his field crew spent 600 hours this year spraying residuals — a 50 percent increase from the past year.

"All these steps help, but they’re not one hundred percent," Jones said. "You still end up with the big weeds. Before you can get them chopped they’ve already put seed on."

One solution proposed by extension weed scientist Ken Smith with the University of Arkansas is a policy of "zero tolerance," a two-step formula that couples hand hoeing with herbicides to prevent pigweed seeds from forming and germinating. So far, the simple method has proven effective on a 68-acre test plot.

But standing in the shed, surrounded by their 1,800 acres of cotton, Jones and Abmeyer are skeptical, doubting the solution’s practicality.

"I guess you could say we’re trying to do zero tolerance, but we just can’t," Jones said.

For now farmers will continue using every weapon in their arsenal of resources while anticipating the next Monsanto innovation, as extension agents encourage sustainable weed management practices for an uncertain future.

"There’s always going to be a hole," Weirich said. "[New technology] may get one weed but maybe not another."


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