Kudzu Weeds Beaten, No Chemicals Needed

By John Upton

As Adam Macon led documentarians through a battered North Carolina wetland, vast criss-crosses of lamentably familiar vines marked the spot where cypress trees had been clearcut years before.

Among the weeds thriving where cypresses once grew were great drapes of kudzu. The invasive vine was introduced in the late 19th century to the U.S., where it became a popular — if regrettable — weapon in the fight against erosion.

Kudzu. Credit: Mike Ball.

Growing as fast as a foot a day, kudzu smothers utility poles, roadside forests and abandoned buildings throughout the U.S. South. Routinely headlining ‘worst invasive species‘ lists, the East Asian invader even has a sprawling nickname: ‘The vine that ate the south.’

“We came from this beautiful cypress forest, where we were knee-deep in water, and there was wildlife chirping all around, to this thicket of exotic invasives,” said Macon, a conservationist who campaigns against the wood-based industries that anchor the economies of some Southern towns, such as paper and wood pellet producers. He described kudzu as a “huge problem” for the region — one that’s “being promoted by increasing urbanization and industrial logging.”

Kudzu is treated using expensive cocktails of powerful herbicides. The cost and effort is so great that it’s often left untreated. Now, though, federal scientists say they have discovered a potent new strategy that appears to work just as well: a combination of mowing, spraying spores of a fungus disease that attacks the weed, and planting native grasses.

Despite its impressive performance as a weed, kudzu cannot establish itself where plants already thrive. That may be its greatest weakness, and it’s one that agricultural scientists are learning to exploit. But if kudzu sets seed in freshly bulldozed land, its vines can burst forth, beating out native plants to dominate fresh territory. It’s the seemingly indelible botanical mark of humanity’s heavy hand.

Illustrated by Perry Shirley.
Illustrated by Perry Shirley.

“Once it gets that foothold,” said Mark Weaver, a U.S. Department of Agriculture plant pathologist based in rural Mississippi, “it’s really aggressive.”

It isn’t enough to kill most of the marauding kudzu. It must be eradicated, or it will spring right back. Given high treatment costs, and low land values in the rural South, property owners have surrendered vast tracts to the weed. Millions of acres have been lost to kudzu throughout the country.

America wants its land back, but it will only do so on the cheap.

The kudzu-infected acres have “low economic value,” Weaver said. “They could have great ecological value, and that value is taken away when you have this monoculture of an exotic invasive weed. But who’s going to come up with the resources to tackle that problem?”

(American kudzu thickets have begun fostering swarms of kudzu bugs, which reached the country only recently. Initial research suggests the bugs could help reduce kudzu populations. The bugs are also attacking nearby crops, increasing the use of insecticides.)

Mark Weaver. Credit: Carol Morris.

For six years, Weaver led American government scientists in their war against kudzu. In experiments involving 99 plots at two kudzu-infested sites a few hours drive apart in Mississippi, Weaver and his USDA colleagues recently reported in Biocontrol Science and Technology paper that their new organic approach worked just as well as traditional chemical onslaughts.

“I think the reason kudzu has been so persistent is that, historically, people battling kudzu with older products ran out of money, ran out of energy and ran out of will,” Weaver said.

Not all of the treatments at the experiment sites were organic. Razed earth alternatives were labeled “Herbicide 3X,” plots sprayed with full doses of three types of more potent herbicides three times one year, and then one more time in the second year. Some plots were treated using newer herbicides that can legally be purchased and used by anybody — no license required. Some sites were mowed; others were not.

(Cartoonishly excessive though Herbicide 3X might sound, the scientists say it could be preferable to more traditional approaches using lower annual doses. That’s because those approaches may require annual spraying for a decade before the weed is eradicated.)

After two years, when the effectiveness of the chemical treatments were compared with the organic alternative, there were no statistically significant differences. The long-term success of the new approach may become clearer in the coming years, since underground kudzu reserves might be lurking beneath the newly planted switchgrass, ready to reemerge as choking vines.

“Having witnessed the ability of kudzu to regenerate from root reserves, I question the long-term outcome of the treatments,” said Cornell University pest management scientist Matthew Frye, who has studied the weed.

Kudzu. Credit: Katie Ashdown.

The fungus sprayed was Myrothecium verrucaria. The pathogen is not yet commercially available. Weaver hopes that will soon change. The disease preys on broadleaf species, such as deciduous trees, meaning it could also attack and kill other plants.

The switchgrass helps prevent erosion, serving the same purpose for which the kudzu was originally planted. It grows quickly. It can withstand some herbicides that kill kudzu. And — perhaps most importantly — it’s not vulnerable to the fungus disease.

“We think the switchgrass may provide a competitive effect,” Weaver said. “If there’s remaining kudzu thats trying to reemerge, we have this canopy now that’s shading it out.”

After switchgrass has cemented its position on the land, other native species can follow it, suggesting that the new organic solution for kudzu infestations may also be the most durable.