More info for the terms: competition, cover, fire management, natural, root crown, tree, vines
Impacts: Kudzu invasion can have severe negative impacts on native plant communities. Because of its rapid growth rate and habit of growing over objects in its path, kudzu can outcompete native plants and quickly dominate habitats where it becomes established [61]. Kudzu infestations are typified by a continuous blanket of monospecific foliage resulting in large-scale alteration of biotic communities [51]. Patches larger than 100 acres (40 ha) now exist in some areas of the South [36]. Plant densities in mature stands may be 1-2 plants per square foot or tens of thousands of plants per acre [11].
Spreading kudzu infestations can eliminate forest cover by enveloping trees along margins of wooded areas. Trees of any size may succumb to competition from arboreal kudzu vines, whose prodigious foliage reduces light availability within the canopy. Infested trees, especially shade-intolerant species such as native pines, are weakened from reduced carbon fixation. Additionally, the accumulation of several years' worth of vines draped within tree crowns provides enough downward tension that even large trees can be pulled to the ground. Once kudzu has gained access to the forest canopy, it is capable of spreading more quickly and aggressively throughout a contiguously forested area during subsequent growing seasons [33]. Presence of Japanese honeysuckle and other arboreal vines can exacerbate kudzu invasiveness. Because kudzu climbs by twining, it can ascend and spread into a forest canopy faster and more extensively by utilizing smaller-diameter vines rather than having to twine around larger-diameter tree boles [33,35].
Kudzu has been characterized as "perhaps the largest nonwoody weed problem in forest management in the South" [36]. Kudzu infestation can be costly to commercial timber producers by severely impacting productivity. While eradication treatments can be expensive, allowing kudzu to continue spreading only increases the acreage impacted and increases the difficulty (and expense) of eradicating older, denser, more intractable infestations [35].
Control: Because kudzu is so invasive, control is best equated with kudzu eradication [32,34]. To ensure complete eradication from a site and prevent reinvasion, every root crown must be killed [34]. Well-established stands may require as long as ten years to eradicate [61].
Kudzu eradication becomes increasingly difficult with increasing age of infestation [32,33,35]. Because kudzu develops large roots that store accumulated starch, older plants may be more resistant to control efforts and require more persistent or intensive management [33]. Vines that have spread vertically into tree canopies are thought to be more vigorous and to sequester starch reserves more rapidly and in greater quantity than prostrate-growing vines [11,33].
Weakening and eventual eradication of kudzu usually requires frequent defoliation by a single or several methods [11]. If managers are limited to a single defoliation treatment per year, it should be conducted in early fall (September in most areas). Kudzu allocates nearly all its resources to stem and foliar growth during the growing season, allocating few resources to root storage until near the end of the growing season. Kudzu recovers from defoliation by allocating root-stored resources to rapidly resume vigorous foliage growth. Defoliation activities conducted during the growing season can help deplete root energy stores and decrease plant vigor. However, fall defoliation is important to reduce resource allocation to roots, and hopefully gain substantial momentum toward eventual eradication [64].
For more information on kudzu control methods, see Mississippi State University Extension Service, Bugwood's Controlling Kudzu in CRP Stands, Controlling Kudzu in Western North Carolina, Southeast Exotic Pest Plant Council, Kudzu in Alabama, and the Virginia Natural Heritage Program websites.
Prevention: No information
Integrated management: No information
Physical/mechanical: Physical or mechanical methods that destroy kudzu foliage can weaken the plant by simultaneously limiting photosynthesis and depleting root-stored energy reserves. For these methods to be effective, especially when used alone, managers should be prepared to apply them persistently and frequently, often for several years. For old, well-established stands, these methods are likely to be ineffective or require many years of intensive application. They are more likely to be effective when used in combination with herbicides.
The time required for eradication is a function of how long it takes to deplete root energy stores. Small, recently established patches (< 10 years old) can be eliminated by persistent weeding or mowing over a period of several (3-4) years [61]. Frequent mowing or cutting, ideally at 2-week intervals, weakens root crowns and inhibits photosynthesis [51]. Frequent mowing can be efficient and effective as long as all root crowns are in areas that are accessible [44].
Disking or cultivating infestations before and after chemical control efforts weakens plants and enhances herbicide effectiveness [33]. Cultivation may be inappropriate in natural areas or on steep or rocky terrain.
Individual plants may be hand pulled, but the entire root crown must be removed to prevent re-establishment [29]. Root systems of small, initial infestations can be excavated with a Pulaski or similar digging tool. All plant material should be removed from the site and destroyed by burning or bagging [51].
Fire: See Fire Management Considerations.
Biological: Intensive grazing can be an effective control measure, where appropriate. Young infestations (< 25 years old) are easier to control with grazing than older stands that have developed very large roots. Steady aboveground herbivory will gradually deplete root energy reserves, inhibit accumulation of new carbon stores by suppressing the amount of photosynthetic tissue, and prevent foliage from spreading into previously uninfested areas. Grazing kudzu infestations for 1 to 2 years prior to herbicide application can help to weaken plants, potentially making chemical control efforts more effective [33,34].
Chemical: Where appropriate, herbicides may be the most effective means of eradicating kudzu, whether used alone or in combination with other methods. Below is a list of herbicides that have been tested and judged effective for controlling kudzu in North America, as well as a brief discussion of important considerations regarding their use. This is not intended as an exhaustive review of chemical control methods. For more information regarding appropriate use of herbicides against invasive plant species in natural areas, see The Nature Conservancy's Weed Control Methods Handbook. For more information specific to herbicide use against kudzu, see Kudzu Eradication and Management, Bugwood's Controlling Kudzu in CRP Stands, Southeast Exotic Pest Plant Council, or the Kudzu in Alabama website.
Chemical Considerations picloram [8,10,32,35] Perhaps the most (overall) effective chemical tested against kudzu [32,35,48]. Specific to broadleaf species; generally does not harm grasses [58]. May be mobile in soil solution and can leach into nearby surface water [31,58]. clopyralid [29,48] More selective than picloram. Has little effect on members of the mustard family (Brassicaceae) and several other groups of broad-leaf plants, as well as grasses and other monocots. Chemically similar to picloram. Has a shorter half-life, but is more water soluble and has lower soil adsorption capacity [58]. fluroxypyr [48] triclopyr [29,35,48] Effective against arboreally established kudzu when applied to vines and foliage around the base of affected trees [35]. metsulfuron hexazinone [29] methyl 2- benzoate [10] tebuthiuron picloram + 2,4-D [32,35] glyphosate [51,61] Nonselective. "Cut-stump" method may be used to reduce mortality of neighboring native plants. For details see Southeast Exotic Pest Plant Council. Low toxicity to animals and relatively immobile in soil. Glyphosate itself may be the least potentially harmful of the above chemicals to the environment, although many surfactants or other adjuvants in some formulations are toxic [58].
Single applications of herbicides can reduce kudzu foliage by up to 2 orders of magnitude. However, continued spot treatment is usually required for several years for complete eradication due to recalcitrant root crowns and substantial root-sequestered carbon reserves that enable kudzu to resprout. Diligent monitoring and follow-up treatments may be required for 10 or more years on some sites [33,42]. Regrowth from surviving root crowns may often be delayed until 2 years after herbicide treatment, with no signs of survival during the 1st growing season. Several years of post-treatment monitoring and retreatment may be needed to ensure 100% mortality [33,48].
In general, herbicides are most effective against kudzu when applied after late May [32], although triclopyr was effective against tree-draped vines when applied in spring prior to the appearance of new growth [35]. Herbicides such as those listed above are likely to be most effective when applied near the end of the growing season when plants are translocating stem and foliar nutrients to root systems for dormant season storage [61]. Dormant-season herbicide application appears to be ineffective in controlling kudzu [48].
Higher herbicide application rates may be required for effective control on clayey or rocky soils or when infestations are older than 10 years [30,33,35]. Kudzu populations growing in a prostrate form, compared with plants growing vertically, are thought to be less vigorous and may be controlled using lower application rates [33,48].
Cultural: Planting grass in the fall following herbicide treatment has been recommended in order to stabilize soil and to provide competition against weakened kudzu plants and other weed species that may be present. Grasses are not injured by some herbicides that can kill kudzu (e.g., picloram or clopyralid) [33].
Planting competing vegetation that provides shade to treated sites, such as dense plantings of pine seedlings, can improve the effectiveness of repeated herbicide treatments [21], potentially reducing treatment duration.