One Australian expert has described it as the "world's greatest herbicide" — a "one-in-a-hundred-year discovery" as important to global crop production as penicillin was to the eradication of disease.

But U.S. farmers, at an alarming rate, are losing their ability to use this herbicide effectively.

The wonder herbicide is glyphosate. Up until a couple of years ago, glyphosate, used in tandem with crops genetically modified to withstand over-the-top applications of this weed killer, enabled farmers not only to reduce their herbicide applications and to farm more profitably, but also to greatly reduce costly levels of conventional-tillage. In a manner of speaking, both the farmers' pocketbooks and their cropland soils suffered less abuse through adoption of this weed control system.

Yet, as she's apt to do, Mother Nature ended up throwing a huge monkey wrench into this system in the form of glophosate-resistant weeds, especially palmer amaranth.

Now, farmers once again find themselves struggling to stay competitive within a global farming economy, even as they're being pressured by public watchdog groups and policy makers to adopt more sustainable farming practices.

At Auburn University, Mike Patterson, an Alabama Cooperative Extension System weed scientist and professor of agronomy and soils, says the weed's threat to this herbicide is presenting a growing number of producers with hard choices.

One thing is certain: Doing nothing is not an option. Patterson cites research showing that uncontrolled weeds can reduce crop yields by as much as 80 percent in cotton, soybean and peanut fields.

"We've got to do something," he says. "Obviously, once you encounter glyphosate-resistant weeds, you have some decisions to make."

The solution, he says, will involve combining the prevailing glyphosate-based system with other herbicide products.

It is both an unavoidable and unattractive option for farmers because it presents them with a challenge they had managed to avoid when they relied on glyphosate — namely high costs.

"Generally speaking, the more herbicide you use, the more it costs — not to mention, the added time and labor of applying them," Patterson says.

Critics of conventional farming methods are calling on producers to abandon the glyphosate system entirely in favor of more sustainable farming practices. However Patterson and weed scientists steadfastly maintain that total abandonment is not a viable option in an era when farmers are struggling to contain operating costs.

In fact, Patterson says farmers already face a major challenge just getting by on the few herbicide products still available to fight weeds.

"Right now, we have only a handful of older products and a couple of newer materials to fight pigweed resistance in row crops," he says. "If these producers lose their registration, preventing farmers from using them, we'll lose one of our last lines of defense."

In the meantime, researchers at the National Soils Dynamic Lab are busy developing sustainable weed-control practices to help manage resistant palmer amaranth.

Patterson cites what he describes as the "cutting-edge" efforts of Andrew Price, who has developed a reduced-tillage approach that also incorporates heavy use of rye grass.

Under this approach, a heavy winter cover-crop of ryegrass is planted following primary fall tillage.

In late April, the ryegrass is rolled flat onto the ground and the spring crop planted directly into it using a no-till system.

Field research has demonstrated the heavy ryegrass mulch shades and prevents the emergence of pigweed and other weeds.

"This tillage system, regardless of the chemical control system chosen, appears to offer the best solution for controlling the resistant pigweed right now," Patterson says.

Crop rotation is also proving effective in some cases, he says.

Patterson says a series of promising technologies are also on the horizon, including a new line of cotton genetically altered to be tolerant to applications of 2,4-D, another effective herbicide.

But producers must wait another four to five years before this is commercially available.

Even then, Patterson says none of these new technologies will provide panaceas.

"Even when they're available, they will not be magic bullets," he says. "They don't control grasses and all weeds in every field."

Whatever strategies producers ultimately choose to control weeds, Patterson says one thing is certain: The use of genetically modified crops in tandem with herbicides will play an integral part in weed control.

"Population is increasing to 9 billion by mid-century and all of them must be fed even as we increase the output of the current farm production system," he says.

"Either we increase food output through the development of new technology or people starve," he says.