Kudzu (Pueraria montana) is a climbing, semi-woody, perennial vine of the legume family. It was imported to the United States from Japan and China in the early 1900s. During the Great Depression, kudzu was heavily promoted for erosion control. In Missouri, kudzu was planted along highways to control erosion and as forage prior to 1970. Today it can be found within select counties, mostly along highways.
Kudzu grows well under a wide range of conditions and in most soil types, except for saturated soils. Preferred habitats are forest edges, abandoned fields, roadsides, and disturbed areas, where sunlight is abundant.
Effects on Natural Communities
Once established, kudzu plants grow prolifically, with a single root crown containing up to 30 vines. Kudzu forms dense mats over the ground, shrubs, mature trees, and buildings, reaching more than 60 feet high. These mats are so dense that very little light gets through, and so kudzu effectively smothers and kills other plants by blocking sunlight. Kudzu can break branches and uproot entire trees under its weight.
It cannot be over emphasized that total eradication of kudzu is necessary to prevent regrowth. As with most aggressive exotic species, eradication requires persistence in monitoring and thoroughness in treating patches during a multi-year program. Revegetation of sites following treatment is an important last step to ensure that any residual kudzu does not reestablish. All landowners in an infestation area must cooperate in a unified program.
Treatment in Areas of Light Infestation
Treatments timed to the plant's life cycle seem to be an important factor in control or eradication strategy. Efforts to control kudzu infestations have included the following methods: cutting, grazing, digging, disking, prescribed burning and application of herbicides.
Roots of mature plants grow too deeply to be affected by freezing. Burning will kill only the very young plants. Young colonies can be eradicated in three to four years if roots are dug, or if plants are overgrazed or persistently and repeatedly cut back during the hottest temperatures of summer. Plants that persist after four years of overgrazing and disking can be spot treated with a recommended herbicide.
Grazing can be an economical alternative to mechanical or chemical treatments in some control situations. It can be effective in combating younger infestations if used persistently during the growing season. Kudzu is readily eaten by most livestock, but cattle grazing has shown the most success in eradication.
Close grazing for three to four years can totally eliminate kudzu when at least 80 percent of the vegetative growth is continuously removed by livestock. It is especially effective if heavy grazing occurs late in the growing season (July–September) when the kudzu is actively sending nutrients to the roots for winter.
For maximum effect, it may be necessary to fence livestock within the area being treated and to provide water and supplemental feed as needed for animal nutrition. Additionally, kudzu vines which are out of reach should be cut and fed to livestock. Any plants that remain after four years of grazing can be spot treated with a recommended herbicide (Miller, 1996).
If the only feasible treatment is herbicides, then systemic chemicals provide the best success. (See the Chemical Control section for details of herbicide treatments.)
After kudzu has wilted from herbicide treatment, a controlled burn can stimulate alternative vegetation to grow. Grasses can be planted in the fall after the first treatment and after every successive treatment to control erosion and to discourage weeds. Healthy stands of grasses will discourage the reestablishment of seedlings and re-sprouting. Pines, hardwoods, and forbs can be planted following eradication of kudzu, allowing an appropriate interval for any residual effects of herbicides to subside.
Treatment of Infestations More Than 10 Years Old
Old kudzu infestations may cover an acre or more with older roots that are too deep for manual removal. Patches more than 10 years old will typically have root crowns (woody knots at the soil surface where stems originate) over 5 cm (2.0 in) in diameter.
In these situations, surface disturbances such as mowing, disking, grazing or burning are unlikely to have much effect. Therefore, few options remain except the application of herbicides.
A prescribed burn in March before herbicide treatment will kill the smallest plants and sever draping vines, leaving roots and new growth a better chance for exposure to chemicals. This is an opportune time to mark the largest roots as well as any hazards in the area slated for treatment. Old roots need heavier herbicide application than young ones.
Best results from chemical treatment occurs if application is done in late summer when flowers appear and nutrients are being actively transported to roots.
Recommended Control in Natural and High Quality Areas
If preservation of a natural area or community limits the use of grazing or large-scale herbicide application, a combination of trimming, disking, and digging as outlined above will set the plants back and perhaps eradicate a new infestation in three to four years.
Foliar application of herbicide using a backpack sprayer will provide more rapid eradication. The expense of restoration of a small area following herbicide use compared to the effects of kudzu spreading over additional acres may weigh in favor of a concentrated herbicide treatment prior to spread. Plant native grasses in the fall after treatment to control erosion and spread of kudzu and invasion of other weedy plants which may colonize the site after kudzu dies.
Many herbicides will kill back the stems and leaves of kudzu; however, most will not provide eradication by killing of the root systems. Testing of 25 herbicides over an eight-year period by Miller (1996) led to the following recommendations:
Open Patches on Level Ground
Tordon 101 Mixture (2,4-D + picloram) and Tordon K (picloram liquid) proved to be the most cost-effective herbicides over the testing period. Both products are applied as foliar sprays which then should be washed from the leaves to the ground by rainfall or spray irrigation of less than one inch within two to five days after application. This allows additional uptake by root systems. Treatment should be done no earlier than late June or July to assure that all stems are actively growing. Tordon 101 Mixture is recommended at a rate of one gallon per acre for younger kudzu infestations and two gallons per acre for patches older than ten years. Tordon K is recommended at a rate of 1/2 gallon per acre in younger patches and 1 gallon per acre in old infestations. A mixture of Tordon 101 Mixture at 1/2 gallon per acre plus Tordon K at 1 quart per acre is also effective on young patches. The rates are again doubled for this mixture on older infestations. Successful eradication has been achieved by applying the Tordon sprays at a volume of 40 to 80 gallons of spray mixture per acre.
Thorough coverage of herbicide is essential to successful treatment. Open patches should be sprayed in a cross-hatch pattern because of the density of foliage. Half of the total solution should be sprayed in one direction and the other half sprayed perpendicular to the first application. Spot treatment with a backpack sprayer can be used on small patches or as a second treatment. The best solutions for spot spraying are either 1 pint Tordon 101 in 4 to 5 gallons of water, or 1/2 pint Tordon K in 4 to 5 gallons of water, or 1 pint Veteran 720 in 4 to 5 gallons of water. These mixtures will be 99-percent effective when vines immediately around root crowns are sprayed to medium wetness.
Re-treatment with the Tordon products is recommended following a successful initial treatment. Many large kudzu roots will not sprout for two years following the first treatment, so re-treatment should occur starting in the third year following the initial treatment. Thus, one year is skipped between the initial treatment and the first re-treatment. Re-treatment application rates are half those of the initial treatment.
Both Tordon products are restricted use herbicides and management agencies may only apply by certified applicators or persons under their direct supervision. Private landowners may purchase and apply for agricultural purposes after training from University Extension Service personnel. Picloram will harm non-target organisms, including crops and other non-target plants. It is very water soluble and may move into groundwater or waterways; therefore, it should not be used near streams, ponds or other sensitive areas. Picloram is particularly damaging to legumes and is relatively persistent in the environment. It can kill new plants introduced into the treated area too soon after application, although many grasses are not affected.
Near Streams, Ponds, Wetlands, or Ditches
Veteran 720 (dicamba) (formerly Banvel 720), a product of Riverdale Chemical Company, is recommended for sites near water, although it should not be sprayed directly onto water. Veteran 720 is a dicot-specific herbicide used as a foliar spray. Application rate is two gallons per acre for younger patches and three gallons per acre for infestations over ten years old. August or September are recommended months for application, but moderate rainfall is required for proper soil activation.
Non-Crop Areas Such As Fencerows and Rights-of-Way
Spike 20P (pellets) and Spike 80W (wettable powder), both DowElanco formulations of tebuthiuron, are slow-acting, residual herbicides that cause vegetation to yellow the first year and die the second year. The Spike herbicides can cause residual effects in the soil for three years. Effective application rate for Spike 80W is 6 to 8 pounds per acre and for Spike 20P, twenty to thirty pounds per acre. Early spring application is recommended. Spike herbicides are non-selective and will kill any desirable plants in the treated area as well as the kudzu, so these products should not be used in natural communities.
Residential and Environmentally Sensitive Areas
Roundup and Rodeo, both Monsanto formulations of glyphosate, are still the safest herbicides for use in residential and environmentally sensitive areas. Both are nonselective, foliar-applied herbicides, with Rodeo being licensed for use over water. Accord, also from Monsanto, is the glyphosate formulation that is labeled for forestry applications. Glyphosate is not as effective on kudzu as the herbicides discussed above, and many years of persistent treatment will be necessary to achieve eradication (Miller 1996).
Transline (clopyralid), from DowElanco, is readily absorbed by foliage and roots and is translocated throughout the plant. This herbicide is targeted to three plant families: legumes, smartweeds, and composites. At 21 ounces per acre, Transline has the benefit that it may be used near trees, grasses, and dicots other than the three target families, without damaging them. Transline has not proven effective in eradicating older infestations of kudzu, but may be helpful in treating young patches and in controlling the spread of older plants.
If not handled properly, herbicides can be injurious to non-target plants as well as to humans and other animals. Use all herbicides and pesticides conservatively, selectively and carefully. Research the proper use thoroughly, follow directions carefully and follow recommended practices for disposal of surplus chemicals and their containers. Consult the Herbicide Handbook of the Weed Science Society of America (Humberg et al. 1989) when considering your special situation.
Failed or Ineffective Practices
Pre-burning, cutting, hand digging and disking are only measures to weaken the roots. They are ineffective alone, but helpful when used in conjunction with systemic herbicides.
Although the Virginia Department of Conservation and Recreation recommends the use of biodegradable glyphosate (Roundup and Rodeo), tests show these products provided only 64-percent control after annual treatment for two years (Miller, 1986). Other trade name products which were tested and were found to have less than 95-percent control of kudzu are Amitrol (87 percent), Krenite (71 percent), Garlon 4 (66 percent), Garlon 3A (65 percent), Oust (63 percent), Esteron 245 (51 percent), 2,4-D (36 percent), Super Brush Killer (36 percent), Maintain CF125 (17 percent), Weedone 2, 4-DP (8 percent). All were sprayed at least twice over two years (Miller, 1986).
Although no biological agents are currently available for kudzu control, efforts are underway to organize funding to screen insects that feed on kudzu in China (J. H. Miller, personal communication). The possibility of future releases of biological control agents probably represents the best hope for long-term control of kudzu.