(CBS News) The dictionary definition of a weed: "A plant considered undesirable, unattractive, or troublesome, especially one growing where it is not wanted." (American Heritage Dictionary)
They insult us by their very existence. They bring out the killer instinct in us. We wage chemical warfare against them, and they win. This story is about the survival of the fittest and who might that be? No doubt about it: Weeds.
"This is an absolute enemy of the state; there's no question whatsoever," said Stanley Culpeper, a weed scientist with the University of Georgia, where his students call him "Dr. Pigweed."
The name of this menace - palmer amaranth, a.k.a. pigweed - an ordinary, manageable nuisance until recently, now a frankenweed.
"Some of 'em are 5 to 6 foot tall, and it's only about 70 days old," said Culpepper. "If you look closely inside, you may or may not be able to see it, but if you look closely inside, here's our cotton crop."
It was completely overwhelmed. The weed's march across the South has devastated cotton and soybean crops.
"If you're off a week, this plant will beat you," said Culpepper. "If you go to the beach and you shouldn't have, this plant will beat you, so it is war, and it's a war of survival because this plant will put us out of business."
As an example, Culpepper showed a stake he planted to measure one weed's height.
"Now you see my stake; that was at the top of that plant four days ago, all right?" Culpepper said. "So that's at least 8 inches in four days."
This relentless killer of crops was discovered eight years ago on a farm in Macon County, Ga.
"In 2012, we confirmed it in 76 Georgia counties, so we went from 500 acres to well over 2 million acres," Culpepper said.
How did it happen?
Ever hear of Roundup, yup that stuff that's advertised on TV.
Roundup, the commercial name for an herbicide called glyphosate, was marketed to farmers as a miracle weed killer. Monsanto, its manufacturer, genetically engineered cotton and soybean seeds so they were Roundup-resistant.
"Roundup used to be just a cure-all for everything," said farmer Harold Johnson.
Johnson farms 1,000 acres in Macon and neighboring Dooly counties. All he had to do was spray on Roundup. His Roundup-resistant crops lived. The pigweed died - until it didn't.
"Just all of a sudden, they would lay down, and then they'd stand right back up, and then it got to the point where they wouldn't even lay down," Johnson said.
The pigweed had genetically engineered itself and become Roundup-resistant too.
Now here's the terrifying part.
"This plant's gonna produce in excess of 500,000 seeds, one female plant," said Culpepper, "and if it survives, it produces a half-a-million seeds."
Desperate growers have deployed their own army against their enemy, like footsoldiers from another century, to hand-weed huge fields. And Dr. Pigweed has a warning.
"This plant has absolutely adapted to everything that we have done so far," Culpepper said.
New York City hopes Larry Cihanek's goats will have better luck against another weed gone wild, an invasive variety of a reed called phragmites plaguing Freshkills Park, an enormous former landfill on Staten Island the city is restoring.
The experiment: To see if the goats will eat their way through 2 acres of the stuff.
"A goat eats about 20 percent of its body weight a day in weeds, so that's a 65/70-pound goat, so that goat's gonna eat 15 to 20 pounds of food a day," said Cihanek. "We have 20 goats. The objective was to do it in six weeks, and they'll certainly do it in six weeks."
It turns out they love phragmites. Six weeks later, success.
Now kudzu, another weed, was actually brought to some places deliberately.
"It was touted, sad to say, by USDA about 100 years ago as being the next miracle plant, and it was brought over from Asia, planted along the embankments of railroad trellises," said Lewis Ziska, a weed scientist with the U.S. Department of Agriculture, "and somewhere along the line in the post-World-War-II era, it kind of got out of hand."
Boy, did it.
"It's about 8 million acres of it now in the United States," Ziska said.
There's so much of it, scientists are trying to turn it into a biofuel. (Really.) But kudzu is not just a bad joke - the weed that ate the South - kudzu is something a lot scarier.
"Now, 50 years ago, you would be hard-pressed to find kudzu north of the Potomac," said Ziska. "Today, it's pretty much everywhere north of the Potomac, and two years ago they found it for the first time in Canada, in southern Ontario."