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Kudzu (/ˈkuːdzu,ˈkʊd-,ˈkʌd-/), also calledJapanese arrowroot orChinese arrowroot,[1][2] is a group of climbing, coiling, and trailing deciduous perennial vines native to much ofEast Asia,Southeast Asia, and some Pacific islands.[2] It isinvasive in many parts of the world, primarilyNorth America.
The vine densely climbs over other plants and trees and grows so rapidly that it smothers and kills them by blocking most of the sunlight and taking root space.[3] The plants are in the genusPueraria, in the pea familyFabaceae, subfamilyFaboideae. The name is derived from theJapanese name for the plantEast Asian arrowroot, (Pueraria montana var.lobata),kuzu (クズ/葛).[4][note 1] Where these plants arenaturalized, they can be invasive and are considerednoxious weeds. The plant is edible, but often sprayed with herbicides.[3]
The name kudzu describes one or more species in the genusPueraria that are closely related, and some of them are considered to bevarieties rather than full species. The morphological differences between the subspecies ofP. montana are subtle; they can breed with each other, and introduced kudzu populationsin the United States apparently have ancestry from more than one of the subspecies.[9][10] They are:
Various other species inPueraria sensu stricto are also known as "kudzu" with an adjective, but they are not as widely cultivated or introduced.[citation needed]
Kudzu has been referred to as "quasi-wild" due to its long history of cultivation, selective breeding into various cultivars, and subsequent return to wild conditions. Some researchers suggest that humans are the main predator of kudzu in its native range, and that human use and cultivation of kudzu both contributes to its success as an invasive species and is a form of biological control for kudzu.[12]
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Kudzu spreads byvegetative reproduction viastolons (runners) thatroot at thenodes to form new plants and byrhizomes.[13] Kudzu also spreads byseeds, which are contained in pods and mature in the autumn, although this is rare.[14] One or two viable seeds are produced per cluster of pods. The hard-coated seeds can remain viable for several years, and can successfully germinate only when soil is persistently soggy for 5–7 days, with temperatures above 20 °C (68 °F).[15]
Once germinated, saplings must be kept in a well-drained medium that retains high moisture. During this stage of growth, kudzu must receive as muchsunlight as possible.[16] 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. Kudzu is able to withstand environments ranging from sunny to shady upon reaching its mature stage; however, forest edges with greater light availability are optimal.[17]
Kudzu's environmental andecological damage results from its outcompeting 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.[18]
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When kudzu invades an ecosystem, it makes theleaf litter morelabile, thereby lessening thecarbon sequestration ability of the soil. This feeds climate change.[19]
Kudzu is an infamous weed in the United States,[20] where it can be found in 32 states.[21] It is common along roadsides and other disturbed areas throughout most of the southeast,[22] as far north as rural areas ofPulaski County, Illinois. The vine has become a sore point inSouthern US culture. Estimates of its rate of spreading differ wildly; it has been described as spreading at the rate of 150,000 acres (610 km2) annually,[23] although in 2015 theUnited States Forest Service estimated the rate to be only 2,500 acres (10 km2) per year.[20]
A small patch of kudzu was discovered in 2009 inLeamington, Ontario, the second-warmest growing region of Canada after south coastal British Columbia.[24][25]
Kudzu was introduced from Japan into the United States at the Japanese pavilion in the 1876Centennial Exposition in Philadelphia.[26] It was also shown at theChicago World's Fair.[21] It remained a garden plant until theDust Bowl era (1930s–1940s), when the vine was marketed as a way for farmers to stopsoil erosion. The newSoil Conservation Service grew seventy million kudzu seedlings and paid $8 an acre (equivalent to $180 in 2024) to anyone who would sow the vine. Road and rail builders planted kudzu to stabilize steep slopes. Farmer and journalist Channing Cope, dubbed "kudzu kid" in a 1949Time profile, popularised it in the South as a fix for eroded soils. He started the Kudzu Club of America, which, by 1943, had 20,000 members. The club aimed to plant 8 million acres (32,000 km2) across the South.[20] Cultivation peaked at over one million acres (4,000 km2) by 1945.[27] Once Soil Service payments ended, much of the kudzu was destroyed as farmers turned the land over to more profitable uses. The Soil Conservation Service stopped promoting kudzu altogether by the 1950s.[20]
Kudzu's ongoing mythos as a mile-a-minute invader is likely due to its visibility coating trees at wooded roadsides, thriving in the sunshine at the forest edge. Despite kudzu's notoriety,Asian privet and invasiveroses have each proved to be greater threats in the United States.[20]
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In Europe, kudzu has been included since 2016 on thelist of Invasive Alien Species of Union concern (the Union list).[28] This means that this species cannot be imported, cultivated, transported, commercialized, planted, or intentionally released into the environment anywhere in the European Union.[29]
There are only some kudzu populations in certain regions of Italy and Switzerland. In Switzerland it occurs almost exclusively inTicino, where it has been found in the wild since at least 1956.[30] Most outbreaks are concentrated aroundLake Lugano andLake Maggiore, where the climate (hot summers and mild winters) encourages its growth. However, outbreaks in peripheral areas such as the Onsernone Valley and Lower Leventina are likely due to the illegal disposal of plant waste. A plan is currently in place to reduce and eventually eradicate the kudzu population in Ticino.[31]
DuringWorld War II, kudzu was introduced toVanuatu andFiji byUnited States Armed Forces to serve ascamouflage for equipment and has become a major weed.[32]
In Australia, Kudzu is also becoming a problem inQueensland,Northern Territory andNew South Wales.[33][34]
InNew Zealand, kudzu was declared an "unwanted organism" and was added to the Biosecurity New Zealand register in 2002.[35]
Destroying the full underground system, which can be extremely large and deep, is not necessary for successful long-term control of kudzu. Killing or removing the kudzuroot crown[36] and all rooting runners is sufficient. 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.[36] These crowns and attached tuberous roots can weigh 400 or 500 pounds (180 to 225 kilograms) and extend up to twenty feet (six meters) into the ground.[37] The age of the crowns is correlated to how deep they are 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 still grow back.[citation needed]
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. Destroying all removed crown material is necessary. 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 new locations.[citation needed]
Close mowing every week, regular heavygrazing for many successive years, or repeatedcultivation may be effective, as this serves to deplete root reserves.[36] If done in the spring, cutting off vines must be repeated. Regrowth appears to exhaust the plant's storedcarbohydrate reserves. Harvested kudzu can be fed to livestock, burned, or composted.[citation needed]
In the United States, the city ofChattanooga, Tennessee, undertook a trial program in 2010 usinggoats andllamas to graze on the plant. Similar efforts to reduce widespread nuisance kudzu growth have also been undertaken in the cities ofWinston-Salem, North Carolina,[38] andTallahassee, Florida.[39]
Prescribed burning is 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,[36] equipment, such as askid loader, can later remove crowns and kill kudzu with minimal disturbance or erosion of soil.[40]
A systemicherbicide, for example,glyphosate,[41]triclopyr,[41] orpicloram,[42] can be applied directly on cut stems, which is an effective means of transporting the herbicide into the kudzu's extensive root system.[43] 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.[44] In large-scale forestry infestations, soil-active herbicides have been shown to be highly effective.[43]
After initial herbicidal treatment, follow-up treatments and monitoring are usually necessary, depending on how long the kudzu has been growing in an area. Up to 10 years of supervision may be needed after the initial chemical placement to make sure the plant does not return.[45]
Since 1998, the United States'Agricultural Research Service has experimented with using the fungusMyrothecium verrucaria as a biologically based herbicide against kudzu.[23] Adiacetylverrucarol spray based onM. verrucaria works under a variety of conditions (including the absence ofdew), 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.[23] Initial formulations of the herbicide produced toxic levels of othertrichothecenes as byproducts, though the ARS discovered that growingM. verrucaria in afermenter on a liquid diet (instead of a solid) limited or eliminated the problem.[23]
Kudzu has been used as a form oferosion control and to enhance the soil. As alegume, it increases thenitrogen in the soil by a symbiotic relationship withnitrogen-fixingbacteria.[46] Its deep taproots also transfer valuable minerals from thesubsoil to the topsoil, thereby improving the topsoil. In the deforested section of the centralAmazon Basin inBrazil, it has been used for improving the soil pore-space in claylatosols, thus freeing even more water for plants than in the soil prior to deforestation.[47]
Kudzu can be used by grazing animals, as it is high in quality as aforage and palatable tolivestock. It can be grazed untilfrost and even slightly after. Kudzu had been used in the southern United States specifically to feed goats on land that had limited resources. Kudzuhay typically has a 22–23% crude protein content and over 60% total digestible nutrient value. The quality of the leaves decreases asvine content increases relative to theleaf content. Kudzu also has low forage yields despite its rate ofgrowth, 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. Fresh kudzu is readily consumed by all types of grazing animals, but frequent grazing over three to four years can ruin even established stands. Thus, kudzu only serves well as a grazing crop on a temporary basis.[3]
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.[48]
Kudzu containsisoflavones, includingpuerarin (about 60% of the total isoflavones),daidzein,daidzin (structurally related togenistein),mirificin, andsalvianolic acid, among numerous others identified.[49] Intraditional Chinese medicine, where it is known asgé gēn (gegen), kudzu is considered one of the50 fundamental herbs thought to have therapeutic effects, although there is no high-qualityclinical research to indicate it has any activity or therapeutic use in humans.[50][51][note 2] Compounds oficariin, astragalus, andpuerarin mitigates iron overload in the cerebral cortex of mice with Alzheimer's disease.[52]Adverse effects may occur if kudzu is taken by people with hormone-sensitive cancer or those takingtamoxifen, antidiabetic medications, ormethotrexate.[51]
The roots containstarch, which has traditionally been used as a food ingredient in East and Southeast Asia. InVietnam, the starch, calledbột sắn dây, is flavoured withpomelo oil and then used as a drink in the summer. InKorea, the plant root is made intochikcha (칡차; "arrowroot tea"), used in traditional medicine, and processed starch used for culinary purposes such as primary ingredient fornaengmyeon (칡냉면). InJapan, the plant is known askuzu and the starch namedkuzuko.Kuzuko is used in dishes includingkuzumochi, mizumanjū, andkuzuyu. It also serves as a thickener for sauces, and can be a substitute for cornstarch.[53]
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The flowers are used to make ajelly that tastes similar to grape jelly.[54][55] Roots, flowers, and leaves of kudzu show antioxidant activity that suggests food uses.[54] Nearby bee colonies may forage on kudzu nectar during droughts as a last resort, producing a low-viscosity red or purplehoney that tastes of grape jelly orbubblegum.[55]
Kudzu has also been used for centuries in East Asia infolk medicine usingherbal teas andtinctures.[26] Kudzu powder is used in Japan to make an herbal tea calledkuzuyu. Kakkonto (Chinese andJapanese: 葛根湯; pinyin:gégēntāng; rōmaji:kakkontō; lit. 'Kudzu Root Soup') is a herbal drink with its origin intraditional Chinese medicine, intended for people with various mild illnesses such asheadache.[26]
Kudzu fiber, known as ko-hemp,[56] is traditionally used to make clothing and paper,[57] and has also been investigated for industrial-scale use.[58][59] Kudzu fiber is abast fiber similar to hemp and linen and has been used for clothing in China for at least 6,000 years and in Japan for at least 1,500 years. In ancient China, kudzu was one of three main clothing and textile materials, with silk and ramie being the other two.[12] Kudzu is still currently used in Japan, primarily to weaveobi worn in the summer.[60]
It may become a valuable asset for the production ofcellulosic ethanol.[61] In theSouthern United States, kudzu is used to makesoaps,lotions, andcompost.[62]
