Introduction

Kudzu is the collective term for several Pueraria species, members of the Fabaceae family. There are multiple species and varieties that can be difficult to distinguish and there is some debate as to whether we even should, or just lump them into one or two more variable species. Regardless of the species debate Pueraria species are highly aggressive and invasive weeds in most places where they are introduced. I have only seen them a few times myself when I was in the eastern USA but there they grow over top of everything, including the other aggressive native and non-native vines found there. Kudzu was encouraged to be planted by the US government in the 1940s for erosion control. Now millions of dollars are spent annually trying to control or remove Kudzu. It is often referred to as “the vine that ate the south”.

Description of Pueraria montana

Leaves & Stems

Kudzu vines are part of the Pueraria genus in the Fabaceae (legume) family of the Fabales order of dicot flowering plants. The most common species in North America is Pueraria montana var lobata, but many people still refer to it as Pueraria montana. The distinctions are subtle, and the vines in North America of all Pueraria species are able to hybridize and distinctions between them become hazy. Once identified to the species level, for the sake of treating it as a noxious weed at least, further classification is rarely necessary and may be left to a professional. The characteristics described here define Pueraria montana in all its variants and subspecies forms.

Pueraria montana is a herbaceous perennial vine that will climb over anything when it is able or sprawl across the ground where there is nothing to climb. It has strong stems that are 0.6 – 2.5 cm in diameter and can be up to 30 m in length. They are incredibly fast-growing, up to 25 cm per day or 18 m in the growing season where the conditions are right.

Kudzu grows from enormous tubers that are up to 2 m long and 18 – 45 cm wide that can weigh up to 180 kg on mature individuals. Like many Fabaceae, it is capable of nitrogen fixation through its root nodules allowing it to grow in poor soil conditions.

Kudzu has pinnately arranged trifoliate leaves 8 – 20 cm long and 5 – 19 cm wide. Its leaflets are ovate to orbicular and are either entire or lobed. Leaflets are pale green above and paler to grayish-green below. They are usually hairy on the abaxial (under) side.

Flowers & Fruits

The fragrant pea-like flowers are reddish, purplish or bluish in color and frequently have yellow patches. Flowers grow from the leaf axils in elongated mostly unbranched inflorescences 10 – 25 cm long. Each flower is 2 – 2.5 cm wide.

The fruits are flattened oblong pods that are 4 – 13 cm long and 0.6 – 1.3 cm wide. They are green when young but turn brown with golden hairs when they mature. The flattened ovoid seeds are visible through the pods and are 4 – 5 mm long by 4 mm wide. They are reddish-brown when mature. While Kudzu is fully capable of pollinator-assisted sexual reproduction it relies mostly on vegetative reproduction to spread.

Similar Species Frequently Confused With

It is difficult to confuse Kudzu with other genera due to the large ovate trifoliate leaves. Sometimes people mistake English Ivy Hedera helix or Poison Ivy Toxicodendron radicans because they have a similar range. However, neither of these are from the Pea family and will have very different flowers. Also, their leaflets in general are much smaller and seldom to never ovate in shape. The only other vine of the pea family that it could be mistaken with is Amphicarpaea bracteata described below.

There are 2 Kudzu species in the Americas, and one of the species has a variant that is similar enough to simply be a variant and in most cases identification down to the variant level is unnecessary. Some people believe Pueraria montana var lobata is the one whose leaflets are lobed, but Pueraria montana itself may also have lobed leaves. Differences are subtle, and many hybridize, so we will leave Pueraria montana identification to the species level only here. The other species is often referred to as Tropical Kudzu and it has a much more limited distribution. It can be differentiated as follows:

• Tropical Kudzu Pueraria phaseoloides – is only found in a handful of locations in the eastern USA and in Veracruz, Mexico. Its flowers are white and purple instead of red, blue or purple with yellow. Its leaflets tend to be much smaller, but can sometimes grow as large, and they tend to be triangular but occasionally may be ovate. And they can also hybridize with the other Pueraria species, further blurring the lines of identification.
• American Hog-Peanut Amphicarpaea bracteata – native to the eastern USA and grows in similar habitats as Kudzu and has trifoliate leaves that look similar, but are usually much smaller. Its flowers are smaller and fewer and are usually white or light pink, never red, blue or purple. Its fruit is usually much smaller and is never golden-hairy.

Native Distribution of Pueraria montana

Pueraria montana is native to East Asia, southeast Asia and some Pacific Islands. It is common in China and Japan.

Habitat Types Where Kudzu is Found

Kudzu can grow in most habitats including forests, riparian areas, roads, fields, along fence rows, and any abandoned lots, buildings, waste areas etc. It is often seen hanging off of trees it has killed, telephone poles, abandoned buildings, vehicles, etc. In China it is often seen on road embankments and in mountains where the land cannot be cultivated.

Kudzu is an opportunistic vine that grows in almost any soil type excluding very wet soils or those with high pH. It can easily grow in nutrient-poor sandy or clayey soils though it prefers well-drained loam.

Human Uses of Kudzu

Kudzu as Food

The large tubers of Kudzu are frequently eaten as a starchy root vegetable. Kudzu leaves, shoots and flowers are often steamed or pickled and eaten as a vegetable.

Kudzu vines are often used as a nutritious forage for livestock.

Kudzu as Medicine

Kudzu root, flower, and leaf have all been used to make medicines, especially in China since at least 200 BC. It is used to treat a variety of ailments including heart and circulatory problems, high blood pressure, chest pain, sinus infections, colds, hay fever, flu and skin problems including allergies, itchiness and psoriasis. It is also sometimes used to treat menopause, muscle pains, measles, dysentery, gastritis, fever, diarrhea, stiff neck, polio, encephalitis, migraine, diabetes and traumatic injury.

Kudzu is a common treatment for hangovers from too much alcohol and has been used in China and Japan for this since 600 AD. It is still widely used today to reduce the symptoms of hangovers including headaches, upset stomach, vomiting, and dizziness.

Kudzu as Ornamental

Kudzu is often used as a garden ornamental. It is sometimes also used to stabilize slopes. Due to its noxious nature, this is done less often now, but still occasionally happens.

Distribution of Pueraria spp in North America

Kudzu was first brought to the USA from Japan at the Japanese pavilion in the 1876 Centennial Exposition in Philadelphia. It was extensively planted in the US in the 1930s and 1940s to control erosion. While multiple species have been introduced and have spread the most abundant species in North America is Pueraria montana var lobata.

In Canada, Pueraria montana has so far only been recorded in Ontario and was only discovered in 2009. Given that it is in Washington state just south of the British Columbia, Canada border it is likely only a matter of time before it appears in British Columbia.

In the USA, Kudzu is found in Washington, Oregon, Nebraska, Kansas, Oklahoma, Texas, Missouri, Arkansas, Louisiana, Illinois, Indiana, Ohio, Kentucky, Tennessee, Mississippi, Alabama, Georgia, Florida, South Carolina, North Carolina, Virginia, Washington DC, West Virginia, Maryland, Delaware, Pennsylvania, New York, New Jersey, Connecticut, Massachusetts, and Maine. It is also found in Hawaii, the Virgin Islands, and Puerto Rico.

In Mexico Pueraria spp so far has been reported in Pueblo, and possibly in Oaxaca, Guerrero, Nayarit, Jalisco and Veracruz but the identifications could not be confirmed without flowers.

Kudzu has now been introduced on every continent except Antarctica.

How Kudzu Spreads

It is primarily spread through long distance by deliberate human introductions as a garden ornamental or landscape plant. It can be ordered online or purchased in local garden nurseries in some states. It is regulated as a pest in Canada and more difficult to purchase, though online sales are seldom regulated.

Seed dispersal is responsible for a small fraction of its spread. Seeds transported in soil will result in some short distance dispersal. However, short distance dispersal occurs mostly through vegetative reproduction as it is capable of rooting from its stem anywhere it touches soil of any quality. It can grow substantially in subtropical areas, up to 18 m in a single growing season. Yard debris piles where careless discarding of vines removed from yards is a significant source of introduction into the wild as is escaping from the yard itself to adjacent land.

Habitats at Risk of Invasion in North America

Any open forest, forest edge, field, abandoned lot, riparian area, etc is at risk of invasion by Kudzu, particularly if they are located next to a source of Kudzu. Because Kudzu primarily reproduces by vegetative spread this slows the rate of invasion quite significantly in terms of distance. In local areas, however, it can rapidly overtake everything.

Kudzu so far has spread widely throughout eastern USA but it will likely spread more north into southern Canada, though so far its range is limited to southern Ontario. Southern Quebec and the Atlantic Provinces are also at risk. It will not invade wetlands or deserts as it cannot tolerate permanently wet soils or extended periods of drought. It can handle drought, however, as long as they are not too severe. It may not invade much of the central North America due to harsher winters. However, with climate change that is unpredictable.

There is still a lot of habitat suitable for it particularly on the west coast of North America including all of the western USA as well as British Columbia, Canada, and parts of Mexico. So far early detection has controlled its spread in these regions.

Impacts of Invasion

Kudzu is a large and aggressive vine that grows over all other vegetation it encounters smothering it and killing it creating monocultures. Even trees are eventually smothered and suffer from loss of photosynthetic capacity until eventually they die. Kudzu, therefore, results in dramatic losses of biodiversity in the area of infestation, negatively affecting native vegetation as well as wildlife that would otherwise feed, nest, or grow on the native plant species it displaces. Once introduced it is notoriously difficult to control.

Potential Benefits of Invasion

Kudzu has often been used to stabilize slopes and does a good job of it. Also, it fixes almost all of its nitrogen and because of the die-back of its leaves it contributes a lot of nitrogen to the soil. After Kudzu is removed, providing you are successful in removing it, the soil is often richer as a result. However, the fact that it smothers and kills all other plant life growing in its vicinity outweighs its benefit as a soil stabilizer and enricher.

Methods to Remove Kudzu

As always prevention is the preferred method of control. It, like most invasive species, is still widely sold online and in some local garden stores. Do not buy or transport any Kudzu plants or roots and never plant them in your yard. It is illegal to purchase in many states and provinces. However, online sales are rarely properly regulated.

If you see them being sold online or in your local garden stores please inform them of their invasive status and ask them to do their part and cease selling them. Ask them to instead sell more native species as ecologically friendly garden alternatives to invasive species.

Once established in an area Kudzu is notoriously difficult to eradicate. Its extremely fast growth and its ability to smother everything in its path combined with its rapid ability to produce roots at any node which touches the soil all makes it difficult to control. Intensive ongoing effort and an integrated management approach are required in order to control or remove Kudzu infestations.

Physical Control of Kudzu

Once already established physical control is very challenging. Physical control of Kudzu is labor-intensive and time-consuming but will cause far less environmental damage than chemical control.

Since Kudzu spreads mostly vegetatively it can be removed in spring, summer, or fall without having to worry much about the seeds. If there are mature seeds on the plants clip them off into a paper bag to keep them contained in case they are fertile and can produce new plants.

The vines should be cut with hand cutters or loppers and pulled down from trees and structures they are climbing on. Then the tubers and all new roots will need to be carefully removed. Since it grows so quickly the biggest challenge in Kudzu removal is that every root crown must be destroyed or the population will recover. Physical removal must be part of an integrated management approach with continuous ongoing monitoring in order to be successful. The area will need to be revisited multiple times the first year to out compete its rapid growth and re-vegetation rate. Then the site will need to be revisited for 4 – 10 years afterward to ensure that every vine that tries to re-establish is destroyed. Even if a single root crown survives and is left to grow within just a few years it could take over the entire area once again.

Mechanical mowing of ground cover patches in flat open areas is a somewhat less labor-intensive approach that can be successful. Mowing repeatedly throughout the growing season for 3 – 5 years in a row will starve out the roots. Eventually, the plants will die without having above-ground material to photosynthesize in order to keep the roots alive.

Prescribed burning can be used in early spring before fire season if your area allows it. This will kill small kudzu plants and sever the climbing stems that are in the trees, poles, etc. Burning may not be effective for larger plants with intensive root systems as the fire may not ever get hot enough. Also, fire alone will not work. It will need to be followed up with physical removal and of course ongoing monitoring.

Disposal of the Shrubs Once Removed

Plants including roots, stems and seeds all must be either burned or solarized before disposal to prevent new populations from beginning at the disposal site. Burning is an effective method to destroy the plant matter, but it is not allowed in some areas or in certain seasons. In this case, solarize them instead. To solarize put the vines into thick black garbage bags and leave them in the full sun for a good 6 – 8 weeks at least to be sure that none of the roots, stems or seeds are no longer viable. Do not try to solarize them on the ground under a tarp. Due to its extremely fast growth rate and rapid rooting at nodes the vines may be able to grow out from under the tarp and start new plants before the ones under the tarp are properly destroyed.

Once solarized the vines can be disposed of at your local garbage dump. Be sure to still inform them that they are an invasive species so that they can be disposed of accordingly, just in case there are still viable stems.

Chemical Control of Kudzu

Chemical applications are almost never an ideal method of control for any invasive species. That is because chemical alteration of the environment often makes the environment more suitable for invasive species than native species. Furthermore, it is often difficult to keep the chemical control method contained so that it does not directly affect any native species that are there during the application process itself. As a result plots where chemical control is used usually show a decrease in species richness. On the other hand, in plots where only physical control is used species riches significantly increases.

Furthermore, there are no chemical control methods that effectively target only Kudzu. And due to the highly aggressive nature, large tuberous roots, and extremely fast growth rate of Kudzu multiple applications are always needed in a single growing season. If even a single root crown survives the treatment and goes undetected within a few years the Kudzu will again take over the area. Therefore applications must continue for 4 – 10 years after the initial treatment. If chemical control alone is used there will be an enormous amount of toxic chemicals being dumped into the environment, making it less suitable for native species.

Chemical control is not recommended.

Biological Control of Kudzu

Biological control involves the use of a predator, herbivore, disease, or some other agent to control an invasive species once it is established in the environment. The problem with biological control is that the agent used must be entirely specific to only the target organism before releasing it into the environment. This is often difficult to determine since the agent of control is also not native to the environment and could behave differently when released there. Take the example of the mongoose and the rat. The mongoose was released in Hawaii in the late 1800s to help control the rat. To this day there are still rats in Hawaii but the mongoose has helped to decimate many native bird populations.

Biological control methods are extremely risky and should only be carried out by professionals after years of rigorous study. The use of biological control methods can never be used alone. They must be part of an integrated pest management approach. This is because the control agent would need to effectively destroy 100% of the vines, their stems, their roots, and their seeds in order to remove Kudzu on its own.

However, with Kudzu biological control is possibly going to be the most effective means with the least amount of effort due to its rapid growth rate and difficulty controlling it by other means. Particularly with large infestations or those near a large source of Kudzu, biological control may be the most desirable. It still of course must be done as part of an integrated management approach that uses physical removal of those unaffected by the biological treatment along with essential ongoing monitoring for multiple years.

Following is a list of biological control methods that have been used in North America in an attempt to help reduce the population densities of Pueraria montana and varieties.

Pathogens both native and non-native to North America have been isolated from Kudzu populations.

• Pseudomonas syringae pv. phaseolicola a plant pathogen native to North America that causes halo blight of legume plants was tested to control Kudzu. It caused high mortality on young and old growth. However, it performed much less well under dry conditions in the field.
• Myrothecium verrucaria is another native fungus that showed greater potential success in the field as it did not require such moist conditions. High mortality rates were observed in the field, and they even performed even better in the heat of summer. Since the application requires the use of a surfactant it keeps the risk of the fungus spreading beyond the application area minimal. However, the fungus did show high toxicity to mammals so extreme caution by professionals is required for application in the field.
• Alternaria and Fusarium fungal species are currently being developed in the USA for potential biological control of Kudzu and other weeds.

Heavy grazing by livestock such as by cows, pigs, horses or goats can also be used to remove Kudzu as part of an integrated management approach. This would only work in groundcover patches though as the animals cannot eat the vines in the trees or on buildings. The animals would need to be fenced in the Kudzu patch for long periods of time to be effective at controlling Kudzu on their own.

Integrated Pest Management & Ongoing Monitoring

Integrated management is always the best approach. In its simplest and least impactful form this involves physical removal methods, possibly biological control methods, replanting, and ongoing monitoring.

Replanting With Native Species is Crucial

In all cases of removal, the site should be planted after the Kudzu is removed. This cannot be done immediately upon the first removal, however, due to the extreme growth rate of Kudzu. But replanting should be commenced in years 2 – 4, depending on the patch dynamics. Replanting with aggressive native species will help keep the Kudzu at bay. However, ongoing monitoring to remove any new seedlings or sprouts of Kudzu will still need to be intensely carried out. If a single root crown survives it will still grow over and smother any vegetation that is planted.

Ongoing Monitoring is Essential

In all cases of invasive Kudzu removal, ongoing monitoring is absolutely essential. Monitoring is important for all invasive species removal, but perhaps Kudzu most of all. The extreme growth and survival rate of stems and roots requires extreme diligence in monitoring. Repeated monitoring for the first couple of years should be carried out on a monthly basis during the growing season to remove any new growth. Then yearly monitoring programs should be put in place for a minimum of 4 years after the initial removal. Monthly monitoring can be reduced to every couple of months in years 2 and on, presuming there are few new individuals being found. An aggressive monitoring program is the only thing that will ensure the success of any biological, physical, or chemical removal or control of Kudzu.

References and Resources

CABI on Pueraria montana https://www.cabi.org/isc/datasheet/45903

Canadensys Plant Search https://data.canadensys.net/vascan/search

Dictionary of Botanical Terms – Lyrae’s Nature Blog Dictionary of Botanical Terms

iNaturalist Plant Search https://www.inaturalist.org/home

Kudzu Photo Smothering Trees in Georgia by Scott Ehardt, Public domain, via Wikimedia Commons https://commons.wikimedia.org/wiki/File:Kudzu_on_trees_in_Atlanta,_Georgia.jpg

RxList.com for Medicinal Uses of Kudzu https://www.rxlist.com/kudzu/supplements.htm

USDA Plants Database https://plants.sc.egov.usda.gov/home

Willis, Lyrae (2022).  Plant Families of North America. Not yet published.

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