Kudzu — Out of Ecological Place and Time
By Claire Payne
Nonnative invasive plants are by definition out of their endemic ecosystem, removed from their natural predators and competitors. If sufficiently invasive, they may interrupt native succession and eventually displace an entire native ecosystem.
Kudzu (Pueraria montana) certainly belongs in this category—it now covers between 4 and 7 million acres in the Southeastern United States; 3 million of these acres are in forests. Where it takes hold, kudzu eventually eliminates all other vegetation, including trees, as it climbs and competes for light. Like the velociraptor in Michael Crichton’s Jurassic Park, kudzu has been re-created out its ecologic and geologic time by an ill-conceived human experiment.
Kudzu has not lived up to the beneficial results anticipated when it was introduced in this country at the Philadelphia Centennial Exposition of 1876. Around the same time, David Fairchild, a plant observer for the USDA, observed extensive acreage of the vine used as food for livestock in Japan. In 1902, he planted kudzu seedlings around his Washington, DC home. Fairchild soon became disenchanted with the plant as it overtook the bushes and pines in his yard, smothering and bending them to the ground. He issued a warning about the invasiveness of the plant, but by the time it was published in 1938, the vine had been widely planted in the South.
In 1907, kudzu baled into hay was exhibited at Jamestown, VA, where Florida farmer C.E. Pleas first encountered the plant’s potential as a bountiful food source for his farm animals. By 1910, Pleas had 35 acres in the vine, and was doing a brisk business selling fodder. He was a strong advocate for kudzu, and sold root cuttings through mail-order catalogs until he died in 1954.
In the 1930s and 1940s, the Soil Conservation Service promoted kudzu as a means of controlling erosion on the gullies created by the deforestation of the South. Kudzu was planted especially heavily in the Piedmont regions of Alabama, Georgia, and Mississippi. The Soil Erosion Service paid farmers $8 per acre to grow kudzu. This subsidized program resulted in more than 1.2 million acres being planted.
By the 1950s, kudzu was recognized as a weed and removed from the list of species acceptable for use under the Agricultural Conservation Program. In 1998, the U.S Congress listed kudzu as a Federal noxious weed.
Impacts on the Ecosystem and the Economy
Kudzu has altered the southern landscape, affecting biodiversity and the cultural and economic framework of the region. In 2002, Coleman Dangerfield, University of Georgia forest economist, estimated that productive forest land overtaken by kudzu represented an economic loss of approximately $48 per acre per year. At that time, the net value of an average stand of pines grown on cutover land for 25 years in the Southeast was approximately $650 per acre, while kudzu control costs exceeded $200 per acre per year for five years. Clearly, costs exceeded potential profit.
Southern Research Station (SRS) plant ecologist James Miller, who has researched herbicides for kudzu control for the last 20 years, estimates power companies alone spend at least $1.5 million per year battling kudzu. The loss of homes, barns, and fields overtaken by kudzu is immeasurable in terms of lost socioeconomic opportunities for farming, homesteading, and gardening.
Biodiversity is a hallmark of the South, an ecological trait imprinted on natives and attractive to visitors from this country and around the world. As Richard J. Blaustein noted in 2001, the South retains remnant populations of many species pushed south from the Upper Midwest and Northeast by the glacier that retreated 18,000 years ago. Kudzu is smothering native plants, grasses, and trees, replacing them with a leguminous woody vine that, once established, can grow about a foot a day.
Kudzu spreads very little by seed, due to predation by spiders and insects. However, its roots thrive in disturbed soil, and the continuing development boom in the South gives the opportunistic vine the avenue it needs—land displaced by construction or agriculture.
The plant sets deep roots rich with carbohydrate reserves capable of withstanding repeated mowing or herbicide applications. Kudzu’s hairy, woody runners include roots at nodes, enabling large storage tubers to develop along the vine’s pathway. An old and uncut plant can have a single root weighing more than 100 pounds, so killing the plant by digging up the roots is a daunting, if not impossible, task.
In China, kudzu is not a pest, possibly because all arable land is cultivated to produce food, not allowing the plant an opportunity to spread. The Chinese dig up the starchy kudzu roots and use them for food and medicinal purposes. Additionally, more than 100 insect species prey on kudzu seeds in China; however, most also feed on plants that produce beans, making them unsuitable as potential biocontrol agents in the United States. Kudzu’s closest relative in the United States is the soybean, which complicates the search for a biocontrol agent considerably.
When forest pathologist Kerry Britton served as project leader for the SRS unit in Athens, GA, she began collaborating with Jianghua Sun, researcher at the Institute of Zoology, Chinese Academy of Sciences, Beijing, China, and entomologist David Orr, North Carolina State University, Raleigh, NC. Looking for ways to control the kudzu infestation in the Southern United States, the team initiated a systematic survey for biocontrol agents in China.
In May 1999, the team selected four survey sites with climatic characteristics similar to the Southeastern United States, focusing on the Anhui Province in Southeastern China, where the climate is similar to Atlanta, GA. Because kudzu grows mostly in mountainous regions in China, the researchers also established a survey site further south in the Guangdong Province. In 2000, a fifth survey site was established in Shaanxi Province, which includes most of the middle stretch of the Yellow River. The climate in the southern part of Shaanxi Province is subtropical and humid with rainy summers.
The researchers chose five sample vines from each site, observing insect feeding, mating, and egg laying behavior at 10-day intervals, May through November. They collected and preserved representative insects and plant specimens of their feeding damage. Defoliation was visually estimated in five 1-foot square areas on each vine. The main vine and branches were monitored for feeding damage and gall formation.
Before an insect imported for potential biocontrol purposes can be released in the United States, researchers conduct extensive tests in U.S. quarantine facilities to ensure that it does not prey on any other American plants. The USDA Animal Plant Health and Insect Service independently analyzes test results to determine whether the insect can be released safely. For the kudzu project, initial tests to determine which insects feed on kudzu were conducted in China, where quarantine facilities are not required for native insects. Project leader and entomologist Jim Hanula of the Insects and Diseases of Southern Forests unit in Athens, GA, has continued working with Jianghua Sun on the project in China. Also involved in the research are Richard Reardon, the Forest Service’s Forest Health Technology Enterprise Team; Gary Mann, USDA Forest Service, International Programs; and Judy Hough-Goldstein, University of Delaware.
Hough-Goldstein and her graduate students are testing a leaf-eating insect from China (Goniocetena tredecimmaculata) in quarantine facilities at the USDA Agricultural Research Center’s Beneficial Insects Introduction Research laboratory in Newark, DE. This summer the team will zero in on whether the soybean is a specific host for the Chinese leaf beetle, which belongs to the family Chrysomelidae. If the beetle eats soybeans, testing will be discontinued.
Nathan Schiff, Southern Station entomologist with the Center for Bottomland Hardwoods in Stoneville, MS, co-authored an identification of kudzu for the 2004 edition of CAB International’s Crop Protection Compendium. Schiff is a proponent of biocontrol, in which a plant’s natural predators are used to keep it under control.
“Biocontrol can be a wonderful success,” says Schiff. “If you can find a bug that eats the plant you want to kill, eats nothing else, and reproduces, it’s self sustaining.” He notes that a host-specific bug that flies is even better, eliminating the problem of distributing the killer to the host.
A classic example of biocontrol success is the demise of cottony cushion scale in California in 1910. The disease was decimating citrus crops. The Vedalia beetle (Rodalia cardinalis) from Australia was introduced, wiped out the scale, and citrus remains one of California’s largest industries.
Chemical treatment to eradicate kudzu is labor intensive and expensive. Until biocontrol is available, grazing sheep are landowners’ best bet for keeping kudzu under control. Though cattle do not like to eat trampled vegetation, goats and pigs do not share that aversion. But it takes skill, logistics, and money to keep grazing animals fenced, herded, and protected. And kudzu climbs, while grazing animals do not.
Kudzu and Culture
Perhaps because of the South’s milder climate, numerous rivers, streams, and lakes, and historical ties to agricultural and forest-based job markets, people feel a deep connection to the land. While millions of acres of the southern landscape have been lost to kudzu, the aggressive plant inspires a significant amount of regional humor and innovation. Southerners enjoy kudzu festivals, where they dance to bands playing bluegrass or country music, eat fried kudzu, and buy baskets woven from the vines. So while scientists and managers work to find the key to controlling the invasion—whether the tool is chemicals, sheep, or biocontrol insects—people driving down the road wonder whether anything’s being down about “this stuff” while enjoying the scent of grape soda.
For more information:
Blaustein, Richard J. 2001. Kudzu’s invasion into Southern United States life and culture. In: McNeeley, J.A., ed. The great reshuffling: human dimensions of invasive species. IUCN, Gland Switzerland and Cambridge, UK: World Conservation Union: 55-62.
Britton, Kerry O.; Orr, David; Sun, Jianghua. 2002. Kudzu. In: Van Driesche, R.; and others. Biological control of invasive plants in the Eastern United States. FHTET-2002-04. Morgantown, WV: USDA Forest Service, Forest Health Technology Enterprise Team: 325-330.
Miller, James H. 2003. Nonnative invasive plants of southern forests: a field guide for identification and control. Gen. Tech. Rep. SRS-62. Asheville, NC: U.S. Department of Agriculture, Forest Service, Southern Research Station. 93 p.
Schiff, N.M.; Abbas, H. 2004. Pueraria montana var. lobata. In: Crop protection compendium [CD-ROM]. Wallingford, UK: CAB International.
Stewart, Doug. 2000. Kudzu: love it—or run. Smithsonian. 31(7): 65-70.