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Skipping Pesticides, Farmers Control Weeds with Plants

A deep green field of rye swayed in a gentle breeze at the U.S. Department of Agriculture’s Beltsville, Maryland, research station last May, blissfully ignorant of its impending doom.

Two-meter-tall stalks sported budding seed heads that would never ripen into amber waves of grain.

With a rattle and a screech, a tractor rolled through the field, knocking the grass flat with a giant red rolling pin. Metal bars curving around the rolling pin crushed the rye and killed it.

Left behind was a solid carpet of flattened rye.

It’s the latest in chemical-free weed control, explained USDA ecologist Steve Mirsky.

“It covers the ground,” he said. “It reduces the amount of light that gets down to the soil surface. And by keeping the ground cooler, it also inhibits the germination of weeds.”

And that’s important, he added, because “weeds are becoming much more of an issue in agriculture again.”

Weeds strike back

It’s the end of an era that began in 1996 with the introduction of genetically modified crops immune to the effects of an herbicide called Roundup. Spraying a field with Roundup kills the weeds but has no effect on the crop.

“That system works and it works well,” Mirsky said. “But the repeated application has the potential to cause resistance, and we’re certainly seeing resistance on the rise across the country.”

More than half of farmers across the country report problems with weeds Roundup no longer kills.

So Mirsky and others are studying an alternative: controlling weeds with plants, not pesticides.

In the fall, they carpet the ground with a so-called “cover crop” like rye. It gets a head start on the weeds.

They let it grow through the spring, then roll it down before planting.

Special equipment cuts or drills through the protective blanket of dead grass to plant the crop.

Pigweed under a blanket

Months later, at harvest time, a walk through the fields showed what rye rolling can do.

In a field that didn’t get the treatment, Mirsky points out a cluster troublesome plants called pigweeds growing as tall as the corn.

“They’ll compete with the corn," he said. "And more importantly, they'll set all this seed, and then you’ll have that many more weed problems.”

One pigweed plant can produce half a million seeds, and an infestation can quickly get out of control.

Meanwhile, walking past the rye-rolled field, he adds, “When you look in there, you can see almost no pigweed because the rye does a wonderful job suppressing it.”

Bonus benefits

And Mirsky says rolling cover crops does more than just fight weeds. The plants rolled down in the spring decay into rich soil, making for better harvests in the fall.

Cotton growers in the pigweed-plagued southeast have adopted rye cover crops to fight resistant weeds.

And Mirsky says one of the big winners could be organic growers, who don’t use herbicides to control weeds.

“For an organic producer in a region where this is going to work, this could have huge implications,” he said.

It will not work everywhere, he adds. But where it does, it offers farmers a new tool to crush an age-old foe.
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    Steve Baragona

    Steve Baragona is an award-winning multimedia journalist covering science, environment and health.

    He spent eight years in molecular biology and infectious disease research before deciding that writing about science was more fun than doing it. He graduated from the University of North Carolina at Chapel Hill with a master’s degree in journalism in 2002.

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