Kudzu in the United States
Kudzu is an invasive plant species in the United States, introduced from Asia with devastating environmental consequences,[1] earning it the nickname "the vine that ate the South".
It has been spreading rapidly in the Southern United States, "easily outpacing the use of herbicide, spraying, and mowing, as well increasing the costs of these controls by $6 million annually".
[4] Kudzu is a perennial vine from the bean family Fabaceae and is native to Asia, primarily subtropical and temperate regions of China, Japan, and Korea,[5][6] with trifoliate leaves composed of three leaflets.
[5] Kudzu's primary method of reproduction is asexual vegetative spread (cloning) which is aided by the ability to root wherever a stem is exposed to soil.
[5][7] These attributes of kudzu made it attractive as an ornamental plant for shading porches in the southeastern United States, but they facilitated the growth of kudzu as it became a "structural parasite" of the South,[7] enveloping entire structures when untreated[11] and often referred to as "the vine that ate the South".
[7] When boll weevil infestations and the failure of cotton crops caused farmers to abandon their farms, kudzu plantings were left unattended.
[7] The climate and environment of the Southeastern United States allowed the kudzu to grow virtually unchecked.
[11] In the United States, kudzu has been used as livestock feed, in fertilizer, and in erosion control, and the vines have been used for folk art.
[11] Kudzu is also used as a food crop in Java, Sumatra, and Malaya, and can be found in Puerto Rico and South America.
[1] In the 135 years since its introduction, kudzu has spread over three million hectares (ha) of the southern United States, and continues to "consume" the south at an estimated rate of 50,000 hectares (120,000 acres) per year, destroying power lines, buildings, and native vegetation, according to a 2006 study.
[21] This claim, however, was disputed in 2015 with the United States Forest Service estimating an increase of 2,500 acres (1,000 ha; 10 km2) per year.
[3] In the United States, kudzu is extensively reported in Alabama, Arkansas, Washington, D.C., Delaware, Florida, Georgia, Illinois, Indiana, Kentucky, Louisiana, Maryland, Missouri, Mississippi, North Carolina, North Dakota, New Jersey, Oregon, Ohio, Pennsylvania, South Carolina, Tennessee, Texas, Virginia, and West Virginia.
Kudzu also forms symbiotic relationships with nitrogen-fixing bacteria to convert atmospheric nitrogen (N2) into ammonium which can be used by surrounding plants.
Now the dominant nitrogen-fixing plant in the eastern United States, kudzu fixes an estimated 235 kilograms per hectare (209+11⁄16 lb/acre) of nitrogen per year, which is an order of magnitude higher than the rates of native species.
In the absence of other plants, nitrogen then builds up in the soil, allowing the maintenance of large leaf areas and high photosynthetic rates.
[7] While little research has been conducted on the impacts of plant invasion on atmospheric conditions, a study conducted at Stony Brook University in New York shows that kudzu has increased the concentration of atmospheric NOx in the eastern United States, which causes a 2 ppb increase in ground level ozone during high temperature events in addition to soil acidification, aluminum mobilization, and leaching of nitrate (NO3−) into aquatic ecosystems.
[7] Kudzu is also a "structural parasite", meaning that, rather than supporting itself, it grows on top of other plants and buildings to reach light.
[22] Most mechanical means of kudzu removal practiced in the southeastern United States involve mowing the vine or cutting it back.
When using this method of kudzu control, all of the plant material must be removed and/or destroyed (burned or fed to cattle) to prevent the vines from taking root and re-growing.
[5] However, chemical treatments are expensive, and killing off the plant completely requires large amounts of herbicides (40–80 US gallons per acre (370–750 L/ha)).
Potential control agents have to be rejected if they are shown in laboratory and field tests to feed on these non-target plants.
[15] Of the diseases that have been identified as potential biological control agents, the fungal pathogen Myrothecium verrucaria has been shown to be very promising.
However, one major drawback of this biological control agent is that it is highly toxic to mammals, so extreme care would have to be taken in handling this organism.
[25] The grazing area where kudzu is to be controlled must be fenced to prevent the livestock from roaming, thereby resulting in a limitation for this method.
