Arkansas farmer Tommy Young says Southern growers have lived through nearly a decade of torment, fighting a destructive, fast-growing weed that can carry a million seeds, grow as tall as an NBA player and is unfazed by several herbicides.

Now that weed — Palmer amaranth — is in five Iowa counties on the state’s border, and agronomists are working to determine whether it is herbicide resistant.

It has the power to choke the state’s economy and environment — and increase prices for consumers.

Here’s how: Even a moderate infestation of Palmer amaranth can rob farmers of about two-thirds of their corn and soybean yields, experts say.

That would be about $11 billion gone from last year’s total $16 billion corn and soybean receipts. That money ripples through some of the state’s most important agricultural businesses, a lineup that includes DuPont Pioneer, Sukup Manufacturing Co. and Deere & Co. Economists estimate that a quarter of Iowa’s $166 billion gross domestic product is tied to farming.

The growth of herbicide resistance means farmers will use more — and potentially more toxic — chemicals to battle the aggressive weed.

Agribusinesses are introducing a new lineup of herbicides and seeds to the battle. Environmental groups worry that those proposed solutions will only worsen the problem.

“Increased herbicide use on the new engineered crops will speed up weed resistance, leaving no viable herbicide alternatives,” said Doug Gurian-Sherman, a senior scientist with the Center for Food Safety.

“This is a dangerous chemical cocktail that, when combined with the current farming system, it’s a recipe for disaster,” Gurian-Sherman, formerly with the Union of Concerned Scientists.

But farmers like Young say they have been forced to adopt less environmentally friendly farming practices, such as increased tillage, to battle herbicide-resistant weeds. Tilling is blamed for increased soil erosion and the loss of nutrients that can make their way into rivers and streams.

Farmers also have turned to older, less-safe chemicals like 2,4-D when glyphosate doesn’t work.

Iowa farmers should be scared, said Young, who had stopped tilling 7,000 acres that his family farms until the discovery of Palmer amaranth four years ago. He said crop rotation and other conservation methods helped him keep the weed at bay for about four years after becoming resistant in the state.

Southern states have plowed under thousands of acres of crops such as cotton in an effort to control Palmer amaranth — and spent millions of dollars hand-weeding it.

“I’m sitting in a sprayer that cost over $350,000,” Young said. “It’s got a computer system that lets me tell you precisely what herbicide I sprayed, how many ounces I sprayed, the wind direction and speed, the field I was in, the humidity.

“I’ve got all this fantastic technology, but nothing to pour in my tank,” said the 50-year-old, who wants government regulators to approve new products from Dow and Monsanto to help battle the weed. “I’m using the same chemicals I used when I was 14.”

Soon, it won’t just be farmers who suffer, he said: “We’re all going to get hurt.”

Many U.S. products are tied to corn and soybeans — from sodas to cereals and fuels — and prices will rise, said Mike Owen, professor of agronomy at Iowa State University. “People don’t recognize almost everything they touch, whether they eat it or they wear it or drive it, has corn or soybeans in it.”

Access to high-quality, low-cost readily available food is “all a function of an effective agricultural system that a weed like the Palmer amaranth could significantly impact,” Owen said.

‘Best herbicide around’ loses power

Nearly 20 weeds in Iowa have developed resistance to herbicides that include glyphosate, a once-in-a-century chemical that Monsanto brought to the market in 1976 under the name Roundup. It killed a broad range of weeds.

Seed companies later introduced genetically modified soybeans, corn, cotton and other crops that were tolerant to glyphosate and other herbicides. It enabled farmers to spray fields for weeds without harming crops.

Seeds also have been modified so crops are resistant to insects and can better withstand environmental forces such as drought. Experts say the seeds have increased yields and, at least initially, enabled farmers to reduce the amount of herbicides and pesticides they used.

Last year, nearly 160 million corn and soybeans acres nationally were planted with genetically modified crops, nearly tripling since 2000, the U.S. Department of Agriculture said in a recent report. That’s about 90 percent of all corn and soybean acres.

Critics blame farmers for creating herbicide-resistant weeds by overusing herbicides such as glyphosate and failing to diversify the crops they plant, relying on products such as Roundup Ready corn and soybeans year after year.

“Even though we warned them, you understand the economics behind it,” said Robert Hartzler, an ISU professor of agronomy. “The current system favors the growth of corn and soybeans,” prompting farmers to leave out rotations of other crops such as winter wheat that could disrupt weed resistance.

“To make a reasonable living, you need to farm large acres, and to farm large acres, you need to cover acres quickly and that involves herbicides. Glyphosate was the best herbicide around,” Hartzler said.

“You couldn’t sit down at a blackboard and come up with a better rotation than we have for weeds to thrive in,” he said.

Hartzler and other scientists say herbicide resistance in weeds was inevitable. “You’ve heard of this guy called Chuck Darwin and evolution?” Owen said.

“If we use one single system, one tool to control a pest, Mother Nature will find a way around that tool,” said Brent Wilson, DuPont Pioneer technical services manager. “That’s just the law of nature.

“It’s too bad that glyphosate is developing resistance, but it shouldn’t surprise us,” Wilson said. “We don’t know of any herbicide that won’t develop resistance over some time.”

Is Palmer already resistant in Iowa?

Hartzler, Owen and others are trying to determine whether Palmer amaranth, discovered in Iowa last year, is resistant to glyphosate.

“If I was a betting man, and I am, I’d say we’ve got glyphosate-resistant Palmer in Iowa,” Owen said. Hartzler believes the superweed is likely growing in more than five counties.

The tiny seed spreads easily — by farm equipment that moves across state lines and fields, in cotton byproducts that are fed to dairy cows, even potentially by birds, experts say.

The states around Iowa are already fighting glyphosate-resistant Palmer amaranth, including Illinois, Missouri and Kansas.

Waterhemp, a similar-looking but wimpier cousin of Palmer amaranth, is resistant to glyphosate and other herbicides in Iowa. “At least 50 percent of fields in Iowa have waterhemp that’s resistant to glyphosate. It’s our No. 1 weed problem,” Hartzler said.

It’s difficult to distinguish between waterhemp and Palmer amaranth, both pigweeds, especially when they’re small, he said. But Palmer amaranth is stronger and faster-growing. It can quickly overrun a soybean crop. Corn is tougher in a matchup.

Waiting even a long weekend to kill Palmer amaranth can result in the plant getting too large to kill with a herbicide. The weed can grow 2 inches a day and needs to be sprayed when it’s 4 to 6 inches in size.

Add spring rains or wind to the equation, and farmers can quickly miss the window, Hartzler said.

Already, U.S. farmers are being forced to use more herbicides to control waterhemp. “We’ve already seen a big leap, and Palmer amaranth will increase it more,” he said.

A Muscatine County farmer who discovered Palmer amaranth last fall decided to mow down part of a soybean field to control it. “He knew if he tried to harvest it, the Palmer amaranth seed would get inside the combine, and it’s nearly impossible to clean it out,” said Hartzler, who determined that weed wasn’t yet resistant to glyphosate. “He didn’t want to spread it to other fields.”

The Iowa Soybean Association has asked farmers to carefully scout fields and nearby ditches for Palmer amaranth. They’re being urged to treat any pigweed like it’s herbicide-resistant, meaning aggressively stamping it out when it’s small.

Young, the Arkansas farmer, said he initially thought he had missed spraying a small patch of weeds that turned out to be resistant to Palmer amaranth. Within a short time, the weed had spread to all the fields he farms.

“If you miss the window of application, you miss the whole boat,” Young said. “I’d say there are very few acres in Arkansas that don’t have resistant Palmer amaranth.”

The cost of using more herbicide, buying tillage equipment, even hiring workers to hand-weed fields, is driving some farmers out of business, he said. “For a lot of farmers, there won’t be a next year.”

Farmers won’t be able to keep up with global demand for their crops as the herbicide-resistant weeds spread and reduce yields. “We’re farming like we did 35 to 40 years ago,” he said. “It’s like using a rotary-dial phone” in a cellphone world.

Palmer amaranth

AGGRESSIVE: Palmer amaranth quickly evolves, adapting to pressures such as herbicides. It’s invasive, with small seeds that are easily spread by machines, feed and birds. It aggressively competes with crops for water and nutrients.

FAST-GROWING: One plant can create 1 million seeds and grow 2 inches a day.

‘A CHRISTMAS TREE’: It can grow up to 7 feet, blocking sunlight from smaller plants such as soybeans. “You could have used it as a Christmas tree,” said agronomist Clarke McGrath, about weeds discovered in southwest Iowa. “That’s what’s so scary about Palmer amaranth. It’s so competitive, it can put on so much biomass, it can take over a field pretty easy.”

EDIBLE: The seeds are a good source of protein.

Herbicide resistance at a glance

14: Weeds in the U.S. that are resistant to glyphosate

160 million: U.S. acres with genetically modified corn and soybeans

70 million: U.S. acres of cropland with glyphosate-resistant weeds in 2013

30,000: Weed species that have the potential to cause farmers trouble

Source: U.S. Department of Agriculture; Union of Concerned Scientists; Dow AgroSciences

Climate change another threat

The nation’s $330 billion agriculture industry will see increased weed, insect and disease pressures from projected rising average temperatures and extreme weather events such as flooding and droughts, according to the latest national climate change report.

Already, farmers like those in Iowa are fighting narrowing windows to prepare fields and plant and harvest crops, said Ricardo Salvador, a senior scientist at the Union of Concerned Scientists. “You’re applying the herbicides, you’re applying the fertilizers, and harvesting all at breakneck speed,” said Salvador, a former agronomy professor at Iowa State University. That will only intensify as catastrophic weather events increase, making farming more difficult.

Herbicide-tolerant crops make farming under those narrowing windows easier. But Salvador believes that will be detrimental. With increased use comes increased weed resistance, he said. “It’s the primary accelerator that will bring about more of these problems.”

Dow AgroSciences disagrees. It says adding to the tools that farmers use is the best way to control weeds and their extensive damage.