Pueraria montana var. lobata
(kudzu)

P. montana, formerly known as P. lobata, is widely known in the USA as ‘kudzu’ is native to East Asia. However, it does not appear to be a significant problem anywhere except in south-eastern USA where it was extensively planted in the 1930s and 1940s for erosion control. Seed dispersal appears to be minor but vegetative growth in subtropical areas can be substantial, up to 18 m per growing season. It is a climbing vine and kills vegetation by completely smothering it, and it will also entirely cover telegraph poles and buildings if left to itself. Once introduced it is difficult to control, especially in forest and marginal habitats. There are three varieties, although only var. lobata is so far known to be invasive, in the USA.

There appears to be some confusing surround the exact limits of the native range. The three varieties of Puerariamontana have overlapping but not identical distributions. Var. lobata is the most widespread, presumed to be native to China, Japan and other parts of South-East Asia, it has spread or been introduced to many tropical regions including Oceania, Central Europe, Central and South America and the continental USA where it is an aggressive and noxious weed. Var. montana and var. thomsonii have more limited ranges in China, Myanmar, Laos, Philippines, Taiwan, Thailand and Vietnam; with var. montana also in Japan (the Ryukyu Archipelago) and var. thomsonii in India, Bhutan and Hawaii (introduced). Kudzu is probably much more widespread in South and Central America but, as it is not considered a pest there, records are not widely reported. The distribution list refers to records of all the varieties and accepts a wider native range than noted by any single source, for example, accepting ILDIS (2007) noting a native range as far south as Queensland, Australia and as far west as Tonga and the Solomon Islands, apparently based on van der Maesen (1985).

Kudzu is an opportunistic climbing vine that grows in numerous habitats including woods, plantation forests, along rivers and roads, on the borders of fields, in abandoned fields, on embankments and along fencerows. It is often seen draped over trees that it has killed, on telephone poles and wires, and on abandoned vehicles and buildings (USDA, 1976). Although kudzu grows well on many soil types including nutrient-poor, sandy and high clay soils, it is most suited to well-drained loamy soils. It does not favour very wet soils, perhaps explaining its absence from the Mississippi Delta, USA, nor soils with high pH (Mitich, 2000). In the USA, kudzu has a wide geographic and climatic range but grows best in areas with at least 1000 mm annual rainfall, mild winters (5-15°C) and hot summers (above 25°C). In China, kudzu is found on road embankments and in mountainous regions where cultivation of crops was not possible.

Kudzu kills plants by smothering, growing over them and blocking out all available light thus preventing photosynthesis. Kudzu kills all plants that it overgrows and is a significant pest in southern USA pine plantations.

Genetics

Heider et al. (2007) found a high level of genetic variation between provenances of P. montana var. lobata in molecular RAPDs studies. An alloenzyme-based population genetics study of US populations showed unexpectedly high heterozygosity. This suggests that populations are the result of multiple introductions and that sexual reproduction probably occurs within populations (Pappert et al., 2000). Some populations with relatively few genotypes displayed an excess of heterozygotes suggesting selection for heterozygosity. A subsequent study showed that highly heterozygous individuals accumulated more biomass and leaf area than less heterozygous individuals (Pappert, 1998).

Physiology and Phenology

The dominant feature of kudzu is its ability to climb over other vegetation including trees. This allows it to maximize light capture for itself while shading its competitors. Kudzu's phenomenal growth is achieved by allocating more biomass to photosynthetic rather than structural tissues (Wechsler, 1974), and using diurnal leaf movements to modulate leaf temperatures, optimizing photosynthesis and reducing water loss (Forseth and Teramura, 1986; 1987). Although kudzu can be found underneath the canopy, it prefers open areas or edges where its photosynthetic rate is highest. Kudzu's climbing mechanism, twining, is adaptive for high light saturation conditions (Carter and Teramura, 1988a,b). When grown under increasing levels of carbon dioxide, kudzu produces more leaf biomass, has longer stems, more branches and the leaves expand sooner, suggesting that it will become even more dominant with increased atmospheric carbon dioxide (Sasek and Strain, 1988,1989).

Reproductive Biology

Most of the spread of kudzu in the USA is due to vegetative growth because seed production is poor. In fact, when kudzu was being planted for erosion control in 1935 it was necessary to import seed (160 kg) from Japan to satisfy the demand for seedlings (Tabor and Susott, 1941). Seed production is poor because flowers are limited to the vertically growing kudzu stems. When pods are formed, the seeds are often killed by native Hemiptera and, less commonly, by a naturalized Asian bruchid seed weevil, Borowiecius ademptus (Thornton, 2001).

In the USA, pollination appears to be adequate by native and naturalized Hymenoptera (Thornton, 2001). In Japan and China, a megachilid bee (Megachile sculpturalis) has been observed pollinating kudzu (Batra, 1998), which is now naturalized in the USA (Mangum and Brooks, 1997). In the 1930s, when seedlings were unavailable, farmers sold seed crowns, that formed wherever kudzu stem nodes contacted the soil, for US $5-7 per thousand (approximately $220 per hectare) (Tabor and Susott, 1941). Takahashi and Kikuchi (1986) noticed that kudzu was one of several species that repopulated Nanakita Hill (Honshu, Japan) after a forest fire. They showed that kudzu seeds germinated at a significantly higher rate than controls if they were soaked in hot water (90°C or 70°C) for 30 seconds.

Associations

Like many legumes, kudzu has a symbiotic relationship with nitrogen fixing bacteria. Erdman (1967) estimated that kudzu fixed 88 kg of nitrogen per hectare, a little less than half that fixed by lucerne (186 kg) and about twice the amount fixed by soyabeans (51 kg), groundnuts (42 kg) or Phaseolus vulgaris beans (40 kg). Nitrogen-fixing bacteria are functionally divided into seven groups. Kudzu is in the cowpea group with groundnuts, velvetbeans (Mucuna pruriens), lima beans (Phaseolus lunatus) and others (Erdman, 1967). Isolates from kudzu root nodules grown on YMA (Yeast Mannitol Agar), do not absorb Congo red and are Gram negative, all attributes consistent with Rhizobium spp. (AD Searle, Wake Forest University, North Carolina, USA, personal communication, 2002).

 

Approximately 25 species of insect have been observed feeding on kudzu (Pemberton, 1988; Britton et al., 2002; and unpublished data from J DeLoach, ARS Grassland, Soil and Water Laboratory, Temple, Texas, USA; G Markin, USDA Forest Service, Bozeman Forestry Sciences, Montana, USA; NM Schiff, USDA Forest Service, Center for Bottomland Hardwoods Research, Stoneville, Mississippi, USA). Of these, seven species are not specific to kudzu (Deporaus sp., Alcidodes trifidus, Sagra femorata, Aristobia hispida, Paraleprodera diopthalma, Anomala corpulenta andEpicauta chinensis); the others are still under investigation and include sawflies, leaf beetles, weevils, longhorned beetles (Cerambycidae), scarab beetles (Scarabeidae) and flat headed borers (Buprestidae) (Britton et al., 2002). There are several reports of arthropods that can live on kudzu but are not considered potential control agents, including the soyabean looper Pseudoplusia includens [Chrysodeixis includens] (Kidd and Orr, 2001), the silver-spotted skipper Epargyreus clarus in the USA (Lind et al., 2001) and the velvetbean caterpillar Anticarsia gemmatalis (Fescemyer and Erlandson, 2003). In Japan, at least three Hemiptera, a parasitoid wasp and two mites develop on or are associated with kudzu (Takasu and Hirose, 1986;Tayutivutikul and Yano, 1989,1990; Shimoda et al., 1997).

In the USA, seeds are eaten by native Hemiptera and a naturalized Asian bruchid seed weevil, Borowiecius ademptus (Thornton, 2001).

Six fungal pathogens have been isolated from kudzu in Anhui Province, China, and may have potential for use as biological control agents for kudzu in the USA (Jiang et al., 2000). A common disease called 'imitation rust' is caused by the fungus Synchytrium puerariae. This pathogen can infect all plant tissues including leaves, stems, flowers and seedpods. Other pathogens included Pseudocercospora puerariicola, the cause of angular leafspot, Cercospora puerario-thomsona, the cause of brown spot, and Phomopsis sp., Colletotrichum lindemuthianum and Colletotrichum sp., causal agents of anthracnose. Virus disease such as leaf mottling and mosaic disease were also found in some parts of China (Jiang et al., 2000).

Soyabean rust (Phakopsora pachyrhizi) is common on kudzu in areas close to soyabean fields in Brazil and Paraguay (Poolpol and Pupipat, 1985; Morel, 2003). A Phytophthora species was isolated from infected root and foliar parts of kudzu in the Korea Republic (YW Lee, Department of Agricultural Biology and Research Center for New Biomaterials in Agriculture, College of Agriculture and Life Sciences, Seoul National University, Suwon, Korea Republic, personal communication, 2003).

 

Animal feed, fodder, forage

• Fodder/animal feed
• Forage

Environmental

• Amenity
• Erosion control or dune stabilization
• Revegetation
• Soil conservation
• Soil improvement

Fuels

• Fuelwood

Human food and beverage

• Flour/starch
• Vegetable

Materials

• Green manure
• Wood/timber

Medicinal, pharmaceutical

• Source of medicine/pharmaceutical
• Traditional/folklore

Kudzu is widely established in eastern USA. It can be dispersed as seeds in soil or as an ornamental plant through mail order. A few small infestations have been eradicated in Oregon (Colquhoun, 2000) and kudzu is a quarantine-restricted plant for that state (USDA-NRCS, 2007). It has recently been recommended for phytosanitary measures in Europe as an A2 pest (EPPO, 2007), as small infestations have been noted from garden escapes in Switzerland. Also, there are concerns about potential future invasion in countries where it has been introduced but has not yet naturalised.

Kudzu is quite distinctive in the field in the USA. To separate kudzu from other species of Pueraria see van der Maesen (1985).

Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.

Control

The combination of extremely fast growth, ability to grow over other plants, root formation where nodes contact the ground, large storage tubers and few natural enemies in the USA makes kudzu a challenge to control. Treatment coverage is probably the most difficult problem. Due to the extreme growth rate, every root crown in the area must be killed or repopulation will occur (Miller and Edwards, 1983). Various cultural and chemical control methods have been attempted and, with intensive effort, it is possible to protect a limited area, however, the vast reservoir of kudzu on the edges of forests and marginal lands, where access is limited, makes it unlikely that kudzu will be permanently controlled by any means other than classical biological control.

Cultural control

Persistent application of cultural methods can be effective in certain situations. Monthly close mowing for two growing seasons effectively starving the roots, can be successful in flat open areas (Ball et al., 1979). Equally, heavy grazing by cows, pigs, horses or goats (Rhoden et al., 1991) can remove kudzu but there are associated problems: animals cannot eat vines growing over trees or in steep areas; they must be penned on the kudzu; watering holes must be provided; and there must be enough livestock to ensure 80% of the kudzu is continuously consumed (Ball et al., 1979; Miller and Edwards, 1983). Although kudzu is nutritious for livestock (Sturkie and Grimes, 1939; Dalal and Patnaik 1963; Corley et al., 1997), cattle do not favour it when it is trampled and horses need to become adapted to it (Hintz, 1993).

Combinations of cultural methods can be effective. The St Regis Paper Co. converted land in Stewart County, Georgia, USA which was partially overrun with kudzu, to a pine plantation in 1967 by burning the kudzu after it was killed by autumn frost, removing merchantable timber and knocking down unmarketable trees so kudzu couldn't grow over them, and then running cattle for 2 years until no kudzu remained on the flat areas. The kudzu that was growing in gullies where the cows could not reach it was chemically treated and loblolly pine (Pinus taeda) seedlings were planted in pasture areas. Yield from areas formerly covered by kudzu exceeded yield from adjacent areas that had no kudzu and soil samples from both areas showed that the kudzu soil was richer in organic matter and had higher levels of all elements tested except phosphorus (Robertson, 1997).
 

Mechanical control

Frequent close cutting will eventually exhaust the plants stored reserves leading to plant death (PIER, 2007).

Chemical control

Effective chemical control of kudzu is possible but it may require repeated application of herbicides over a period of 4-10 years (Nelson, 1997). Many herbicides have been tested against kudzu (Davis and Funderburk, 1964; Martin and Miller, 1981; Michael, 1982;Miller, 1982,1985,1986,1988; Miller and Edwards, 1983; Miller and True, 1986;Smith, 1988,1990; Kay and Hoyle, 1997). Selection of an appropriate treatment depends on several factors including age and vigour of the kudzu, roughness of the terrain, proximity to streams or ponds and the value of other crops or trees present on the site. As with cultural control, kudzu will return if even a single root crown is left untreated, though several procedures can improve the effectiveness of herbicide treatment. Prescribed burning early in the spring will kill small kudzu plants and sever stems draped over trees. It will also reveal application hazards, which can then be marked, and expose root crowns. The size of root crowns indicates the age of the kudzu patch. Typically, patches more than 10 years old require twice as much herbicide as younger patches (Miller, 1991). If possible, trees should be logged prior to treatment and draping stems should be severed. The recommended application technique includes outlining the area to be treated followed by back and forth overlapping swaths and then cross-wise spray swaths perpendicular to the initial swaths, and near streams, application should follow the stream shape using double overlapping swaths (Miller, 1991).

Biological control

Biological control is an important element of an integrated kudzu management system, and many pathogens have been isolated from kudzu and include microorganisms native and non-native to the USA. Those native to the USA include Pseudomonas syringae pv. phaseolicola [P. savastanoi pv. phaseolicola] which causes halo blight of legume plants such as beans and kudzu. The symptoms are described as small necrotic leaf spots surrounded by bright halos of chlorotic tissue. This pathogen was tested for its potential as a biological control agent of kudzu by Zidak and Backman (1996). They found it was capable of causing mortality on both young and old kudzu seedlings, however, secondary infections under dry conditions in the field were very limited.

Boyette et al. (2001,2002) tested the effectiveness of another US native fungus, Myrothecium verrucaria, as a biological control agent for kudzu. This fungus was isolated in 1997 from infected Senna obtusifolia, and showed dramatic potential for biological control of various weed species when formulated, even in the absence of environmental dew (Walker and Tilley, 1997). The USDA-ARS biological control team showed that M. verrucaria applied at a high spore rate of 2x10⁸ conidia/ml caused greater than 90% mortality of both young and old kudzu seedlings. They also determined that the disease severity increased with an increase in temperature to 30-40°C, suggesting that this mycoherbicide could be very active in the summer in the southern USA. The virulence of M. verrucaria against kudzu was increased in formulation with an organosilicon surfactant to cause 100% mortality of kudzu in the greenhouse and in the field 2 weeks after spraying at a rate of 2x10⁷. As fungal activity requires the surfactant, the risk of the fungus spreading beyond the sprayed field is minimal. Eight to ten toxic macrocyclic trichothecenes (Abbas et al., 2001,2002) were found in extracts of M. verrucaria, the specific number depending on the type of tissue used, growing conditions and type of growth medium (Abbas et al., 2001). In all cases at least two very potent toxins were produced, however, none of the mycotoxins were detected in target plant tissues (kudzu, Senna obtusifolia or soyabean) after spraying with M. verrucaria. The combination of surfactant-limited activity, high efficacy and lack of residual toxins add to the appeal of M. verrucaria as a potential biological central agent for kudzu. However, concerns about the toxicity of the macrocyclic trichothecenes to humans and livestock (Jarvis et al., 1985) and the high mammalian toxicity as noted by Abbas et al. (2002) indicate that extreme care should be exercised when handling mycelium, spores or any other type of formulation for field application. Further investigations may discover other strains and/or techniques for producing fungus inoculum free from potent toxins.

Some isolates of Colletotrichum gloeosporioides [Glomerella cingulata] are well established as biocontrol agents of various weeds including the mycoherbicide 'Collego' (Smith, 1986). A specific isolate of this fungus was obtained from kudzu in Houston County, Georgia, USA, and its virulence was increased by several selections for growth on a Czapek Dox medium amended with kudzu extract. This isolate showed dramatic effects on both leaves and vines and produced conidia in a pycnidium which could be used for secondary infection (Farris and Reilly, 2000). In the USA, several fungi, including Alternaria and Fusarium species, are being developed as potential biocontrol agents against a variety of weeds and have been tested against kudzu. In greenhouse and field experiments, kudzu seedling mortality has been achieved with preparations of A. helianthi, F. solani and F. polyphialidicum (Abbas et al., 1991; Abbas et al., 1995a,b,1996a,b; Abbas and Barrentine, 1995; Abbas and Boyette, 1996). Although an attempt was made to use the soyabean rust pathogen Phakopsora pachyrhizi for biological control of kudzu in the USA, there is a concern that it might affect soyabean crops (G Hartman, National Soybean Research Center, Urbana, Illinois, personal communication, 2003).

28/11/2007 Updated by:

Nick Pasiecznik, Consultant, France