Kudzu (; also called Japanese arrowroot or Chinese arrowroot) is a group of climbing, coiling, and trailing perennial vines native to much of East Asia, Southeast Asia, and some Pacific islands, but invasive in many parts of the world, primarily North 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. The plants are in the genus Pueraria, in the pea family Fabaceae, subfamily Faboideae. The name is derived from the Japanese name for the plant East Asian arrowroot (Pueraria montana var. lobata), or ? ('kuzu').[note 1] Where these plants are naturalized, they can be invasive and are considered noxious weeds. The plant is edible, but often sprayed with herbicides.
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:
Kudzu spreads by vegetative reproduction via stolons (runners) that root at the nodes to form new plants and by rhizomes. Kudzu also spreads 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 can successfully germinate only when soil is persistently soggy for 5-7 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, kudzu must 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.
Kudzu has been used as a form of erosion control and 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 22-23% crude protein content and over 60% total digestible nutrient value. The quality of the leaves decreases 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. 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.
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 isoflavones, including puerarin (about 60% of the total isoflavones), daidzein, daidzin (structurally related to genistein), mirificin, and salvianolic acid, among numerous others identified. In traditional Chinese medicine, where it is known as gé g?n (gegen), kudzu is considered one of the 50 fundamental herbs thought to have therapeutic effects, although there is no high-quality clinical research to indicate it has any activity or therapeutic use in humans. Adverse effects may occur if kudzu is taken by people with hormone-sensitive cancer or those taking tamoxifen, antidiabetic medications, or methotrexate.
The roots contain starch, which has traditionally been used as a food ingredient in East and Southeast Asia. In Vietnam, the starch called b?t s?n 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 manj?, 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 as folk medicine using herbal teas and tinctures. Kudzu powder is used in Japan to make an herbal tea called kuzuyu. Kakkonto (Chinese and Japanese: ; pinyin: gég?nt?ng; r?maji: kakkont?; "Kudzu Root Soup") is a herbal drink with its origin in traditional Chinese medicine, intended for people having various mild illnesses, such as headache.
Kudzu's environmental and ecological 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.
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. In the 1930s and 1940s, the vine was rebranded as a way for farmers to stop soil erosion. Workers were paid $8 per acre to sow topsoil with the invasive vine. The cultivation covered over one million acres (4,000 km2) of kudzu.
It is now common along roadsides and other disturbed areas throughout most of the southeastern United States, as far north as rural areas of Pulaski County, Illinois. 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 (10 km2) per year.
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 kudzu root crown 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. 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.
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.
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. Harvested kudzu can be fed to livestock, burned, or composted.
In the United States, the city of Chattanooga, Tennessee undertook a trial program in 2010 using goats and llamas to graze on the plant. 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 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 kill kudzu with minimal disturbance or erosion of soil.
A systemic herbicide, for example, glyphosate, triclopyr, or picloram, 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 an area. Up to 10 years of supervision may be needed 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 that growing M. verrucaria in a fermenter on a liquid diet (instead of a solid) limited or eliminated the problem.