Kudzu

Definition: Fast-growing perennial vine indigenous to Asia that has been imported to other areas worldwide and is often considered a weed

As an introduced species in North America, kudzu has been both beneficial and detrimental to the environment. Initially planted widely to combat soil erosion, kudzu proved difficult to control, and its spread over vast areas of the United States had negative impacts on native plant and animal species as it added harmful chemicals to soil, water, and atmosphere. Efforts to find environmentally benign methods of eradicating kudzu are ongoing.

Kudzu (Pueraria montana ) vines can reach more than 30.5 meters (100 feet) in length, growing by 30 centimeters (12 inches) daily in summers and attaining widths of 25 centimeters (10 inches). The mature roots of kudzu are often several inches thick and can reach depth of 3 meters (10 feet); they may weigh as much as 136 kilograms (300 pounds). Although kudzu flowers and produces seeds, the plant’s resilience depends on root crowns that are the sources of most new vines.

North Americans began importing kudzu from Japan and China during the late nineteenth century. During the early twentieth century, the U.S. Department of Agriculture (USDA) and land-grant colleges studied kudzu and issued reports on the cultivation of kudzu for livestock fodder. By the 1920’s, conservationists recognized kudzu’s potential to prevent agricultural fields from losing topsoil. During the 1930’s, the Soil Conservation Service and the Civilian Conservation Corps planted thousands of hectares of kudzu as an erosion-control measure. Within decades, however, it became clear that kudzu was having detrimental impacts on the environment. The USDA declared kudzu an invasive species by 1953, and the transport of kudzu across state lines was not allowed without permission of the USDA secretary.

Kudzu overwhelms other plants, including crops, as it spreads into their territory, blocking sunlight and interfering with chlorophyll production. Trees are vulnerable to kudzu vines, which can damage tree branches and trunks. Kudzu also alters habitats, often causing indigenous plant species to die and displacing animals, reducing biodiversity. Further, the atmosphere is harmed when the isoprene released by kudzu becomes ozone. Kudzu has also been found to admit nitrogen pollutants, including ammonia.

By 2013, kudzu covered more than 1.2 million hectares (3 million acres) of land in the United States. Annually, new kudzu growth expands by more than 20,000 hectares (or roughly 50,000 acres). Satellite images reveal kudzu growth around the world, and the International Union for Conservation of Nature includes kudzu in its Global Invasive Species Database. Yearly economic losses associated with kudzu have been estimated at approximately $500 million.

Initially, the methods used to remove kudzu involved herbicides, burning, or mowing; most proved ineffective in the long run, as they killed leaves and damaged vines but left behind underground roots that produced new growth. Researchers and the U.S. Forest Service have worked to find methods of eradicating kudzu that do not harm the environment. With the realization that kudzu growth is controlled in Asia by indigenous predators absent in the United States, scientists began to investigate various biocontrols, such as exposing kudzu to viruses, bacteria, or fungi with diseases.

Entomologists have focused on attacking kudzu with insects that will not damage other plants and disrupt ecosystems. In the late 1990’s, after consulting with scientists at the Chinese Academy of Sciences to identify Asian insects that eat kudzu, one group of researchers at North Carolina State University began a study that involved inserting wasp eggs into soybean looper caterpillars, which feed on kudzu. The larvae increased the caterpillars’ appetites and thus their consumption of kudzu leaves; because the plants had to replenish their foliage repeatedly, they used up the starch reserves in their roots and eventually died.

By the early twenty-first century, scientists began to study the potential for using kudzu in the production of biofuels. Research conducted by the USDA and the University of Toronto showed that more gallons of ethanol could be produced from the harvest of one hectare of kudzu than from the harvest of one hectare of corn, the crop most often used in ethanol production in the United States. Concerns have been voiced about the difficulty of controlling kudzu as a crop, but advocates of using kudzu for ethanol production note that harvesting the plant on a large scale would reduce harmful emissions while at the same time creating an opportunity for income generation. In 2010 the Tennessee company Agro-Gas Industries announced plans to explore using kudzu to make ethanol.

Bibliography

Forseth, Irwin N., Jr., and Anne F. Innis. “Kudzu (Pueraria montana): History, Physiology, and Ecology Combine to Make a Major Ecosystem Threat.” Critical Reviews in Plant Sciences 23, no. 5 (2004): 401-413.

Sage, Rowan F., et al. “Kudzu [Pueraria montana (Lour.) Merr. Variety lobata]: A New Source of Carbohydrate for Bioethanol Production.” Biomass and Bioenergy 33, no. 1 (January, 2009): 57–61.

Sun, Jiang-Hua, et al. “Survey of Phytophagous Insects and Foliar Pathogens in China for a Biocontrol Perspective on Kudzu, Pueraria montana var. lobata (Willd.) Maesen and S. Almeida (Fabaceae).” Biological Control 36, no. 1 (January, 2006): 22–31.