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Kudzu (/ˈkʊdzuː/, also called Japanese arrowroot) is a group of plants in the genus Pueraria, in the pea family Fabaceae, subfamily Faboideae. They are climbing, coiling, and trailing perennial vines native to much of eastern Asia, Southeast Asia, and some Pacific islands. The name comes from the Japanese name for the plants, kuzu (クズ or 葛?), which was written "kudzu" in historical romanizations. Where these plants are naturalized, they can be invasive and are considered noxious weeds. The plant climbs over trees or shrubs and grows so rapidly that it kills them by heavy shading. The plant is edible, but often sprayed with herbicides.
Taxonomy and nomenclature
The name kudzu describes one or more species in the genus Pueraria that are closely related, and some of them are considered to be varieties rather than full species. The morphological differences between them are subtle; they can breed with each other, and introduced kudzu populations in the United States apparently have ancestry from more than one of the species. They are:
P. lobata (P. montana var. lobata)
P. thomsonii (P. montana var. chinensis)
Origin in the United States
Kudzu was introduced to the United States as an ornamental bush and an effortless and efficient shade producer at the Philadelphia Continental Exposition in 1876. In the 1930s and '40s, the vine was rebranded as a way for farmers to stop soil erosion. Southern farmers were given about eight dollars an acre to sow topsoil with the invasive vine. The cultivation covered over one million acres of kudzu.
Kudzu spreads by vegetative reproduction via stolons (runners) that root at the nodes to form new plants and by rhizomes. Kudzu will also spread by seeds, which are contained in pods and mature in the autumn, although this is rare. One or two viable seeds are produced per cluster of pods. The hard-coated seeds can remain viable for several years, and will successfully germinate only when soil is persistently soggy for five to seven days, with temperatures above 20 °C (68 °F). Once germinated, saplings must be kept in a well-drained medium that retains high moisture. During this stage of growth, it is critical for kudzu to receive as much sunlight as possible. Kudzu saplings are sensitive to mechanical disturbance, and are damaged by chemical fertilizers. They do not tolerate long periods of shade, or high water tables.
Soil improvement and preservation
Kudzu has been used as a form of erosion control and also to enhance the soil. As a legume, it increases the nitrogen in the soil by a symbiotic relationship with nitrogen-fixing bacteria. Its deep taproots also transfer valuable minerals from the subsoil to the topsoil, thereby improving the topsoil. In the deforested section of the central Amazon Basin in Brazil, it has been used for improving the soil pore-space in clay latosols, thus freeing even more water for plants than in the soil prior to deforestation.
Kudzu can be used by grazing animals, as it is high in quality as a forage and palatable to livestock. It can be grazed until frost and even slightly after. Kudzu had been used in the southern United States specifically to feed goats on land that had limited resources. Kudzu hay typically has a 15–18% crude protein content and over 60% total digestible nutrient value. The quality of the leaves decreases, however, as vine content increases relative to the leaf content. Kudzu also has low forage yields despite its rate of growth, yielding around two to four tons of dry matter per acre annually. It is also difficult to bale due to its vining growth and its slowness in shedding water. This makes it necessary to place kudzu hay under sheltered protection after being baled. Kudzu is readily consumed by all types of grazing animals, yet frequent grazing over three to four years can ruin stands. Thus, kudzu only serves well as a grazing crop on a temporary basis.
Kudzu fiber has long been used for fiber art and basketry. The long runners which propagate the kudzu fields and the larger vines which cover trees make excellent weaving material. Some basketmakers use the material green. Others use it after splitting it in half, allowing it to dry and then rehydrating it using hot water. Both traditional and contemporary basketry artists use kudzu.
Kudzu contains a number of useful isoflavones, including puerarin, about 60% of the total isoflavones, and also daidzein (an anti-inflammatory and antimicrobial agent) and daidzin (structurally related to genistein). It has shown value in treating migraine and cluster headaches. It is recommended for allergies and diarrhea.
In traditional Chinese medicine, where it is known as gé gēn (Chinese: 葛根), kudzu is considered one of the 50 fundamental herbs. It is used to treat tinnitus, vertigo, and Wei syndrome (superficial heat).
Kudzu has been used as a remedy for alcoholism and hangover. The root was used to prevent excessive consumption, while the flower was supposed to detoxify the liver and alleviate the symptoms afterwards. However, a 2007 study suggested that the use of the kudzu root is inappropriate as a hangover remedy due to increased acetaldehyde accumulation through mitochondrial aldehyde dehydrogenase inhibition. Some hangover remedies are marketed with kudzu as one of their active ingredients.
It has also shown potential in animal models of Alzheimer's disease.
Food and beverage
The roots contain starch, which has traditionally been used as a food ingredient in East Asia. In Vietnam, the starch called bột sắn dây is flavoured with pomelo oil and then used as a drink in the summer. In Japan, the plant is known as kuzu and the starch named kuzuko. Kuzuko is used in dishes including kuzumochi, mizu manjū, and kuzuyu. It also serves as a thickener for sauces, and can substitute for cornstarch.
The flowers are used to make a jelly that tastes similar to grape jelly. Roots, flowers, and leaves of kudzu show antioxidant activity that suggests food uses. Nearby bee colonies may forage on kudzu nectar during droughts as a last resort, producing a low-viscosity red or purple honey that tastes of grape jelly or bubblegum.
Kudzu has also been used for centuries in East Asia to make herbal teas and tinctures. Kudzu powder is used in Japan to make an herbal tea called kuzuyu.
Kudzu fiber, known as ko-hemp, is used traditionally to make clothing and paper, and has also been investigated for industrial-scale use. The stems are traditionally used for basketry.
It may become a valuable asset for the production of cellulosic ethanol. In the Southern United States, kudzu is used to make soaps, lotions, and compost.
Ecological damage and roles
Kudzu's environmental and ecological damage results from acting through "interference competition", meaning it outcompetes other species for a resource. Kudzu competes with native flora for light, and acts to block their access to this vital resource by growing over them and shading them with its leaves. Native plants may then die as a result.
Changes in leaf litter associated with kudzu infestation results in changes to decomposition processes and a 28% reduction in stocks of soil carbon, with potential implications for processes involved in climate change.
Kudzu was introduced from Japan into the United States at the Japanese pavilion in the 1876 Centennial Exposition in Philadelphia. It is now common along roadsides and other disturbed areas throughout most of the southeastern United States. Estimates of its rate of spreading differ wildly; it has been described as spreading at the rate of 150,000 acres (610 km2) annually, although in 2015 the United States Forest Service estimated the rate to be only 2,500 acres per year.
Kudzu was discovered July 2009 in a patch 110 m (360 ft) wide and 30 m (98 ft) across, on a south-facing slope on the shore of Lake Erie near Leamington, Ontario, about 50 km (31 mi) southeast of Windsor. Leamington is located in the second-warmest growing region of Canada after south coastal British Columbia.
Ecologist Gerald Waldron made the Leamington find while walking along the beach. He recognized the kudzu instantly, having read about its destructive expansion in the southeastern United States.
During World War II, kudzu was introduced to Vanuatu and Fiji by United States Armed Forces to serve as camouflage for equipment and has become a major weed.
Kudzu is also becoming a problem in northeastern Australia, and has been seen in isolated spots in Northern Italy (Lake Maggiore).
In New Zealand, kudzu was declared an "unwanted organism" and was added to the Biosecurity New Zealand register in 2002.
For successful long-term control of kudzu, it is not necessary to destroy the underground system, which can be extremely large and deep. It is only necessary to use some method to kill or remove the kudzu root crown and all rooting runners. The root crown is a fibrous knob of tissue that sits on top of the roots. Crowns form from multiple vine nodes that root to the ground, and range from pea- to basketball-sized. The older the crowns, the deeper they tend to be found in the ground. Nodes and crowns are the source of all kudzu vines, and roots cannot produce vines. If any portion of a root crown remains after attempted removal, the kudzu plant may grow back.
Mechanical methods of control involve cutting off crowns from roots, usually just below ground level. This immediately kills the plant. Cutting off the above-ground vines is not sufficient for an immediate kill. It is necessary to destroy all removed crown material. Buried crowns can regenerate into healthy kudzu. Transporting crowns in soil removed from a kudzu infestation is one common way that kudzu unexpectedly spreads and shows up in various locations.
Close mowing every week, regular heavy grazing for many successive years, or repeated cultivation may be effective, as this serves to deplete root reserves. If done in the spring, cutting off vines must be repeated. Regrowth appears to exhaust the plant's stored carbohydrate reserves. Cut kudzu can be fed to livestock, burned, or composted.
The city of Chattanooga, Tennessee, has undertaken a trial program using goats and llamas to graze on the plant. As of 2007, the goats are grazing along the Missionary Ridge area in the east of the city. Similar efforts to reduce widespread nuisance kudzu growth have also been undertaken in the cities of Winston-Salem, North Carolina and Tallahassee, Florida.
Prescribed burning is also used on old extensive infestations to remove vegetative cover and promote seed germination for removal or treatment. While fire is not an effective way to kill kudzu, equipment, such as a skid loader, can later remove crowns and thereby kill kudzu with minimal disturbance of soil.
A systemic herbicide, for example, glyphosate, Triclopyr, or Tordon, can be applied directly on cut stems, which is an effective means of transporting the herbicide into the kudzu's extensive root system. Herbicides can be used after other methods of control, such as mowing, grazing, or burning, which can allow for an easier application of the chemical to the weakened plants. In large-scale forestry infestations, soil-active herbicides have been shown to be highly effective.
After initial herbicidal treatment, follow-up treatments and monitoring are usually necessary, depending on how long the kudzu has been growing in the area. It may require up to 10 years of supervision after the initial chemical placement to make sure the plant does not return.
Since 1998, the United States Department of Agriculture, Agricultural Research Service (ARS) has experimented with using the fungus Myrothecium verrucaria as a biologically based herbicide against kudzu. A diacetylverrucarol spray based on M. verrucaria works under a variety of conditions (including the absence of dew), causes minimal injury to many of the other woody plants in kudzu-infested habitats, and takes effect quickly enough that kudzu treated with it in the morning starts showing evidence of damage by midafternoon. Initial formulations of the herbicide produced toxic levels of other trichothecenes as byproducts, though the ARS discovered growing M. verrucaria in a fermenter on a liquid instead of a solid diet limited or eliminated the problem.
This article was based in part on content from public domain web pages from the United States National Park Service and the United States Bureau of Land Management
Species Profile - Kudzu (Pueraria montana var. lobata), National Invasive Species Information Center, United States National Agricultural Library. Lists general information and resources for Kudzu.
Ontario's Most Unwanted - Kudzu (Pueraria montana var. lobata), Ontario Invasive Plant Council. Lists information and resources for Kudzu in Ontario.
Kudzu in Rotation with Corn and Small Grain - NCSU College of Agriculture and Life Sciences.