Written by: Brandon Holden, Alison Kilpatrick, Jonathan Sukhra, Lily Vuong
The history of Kudzu, Pueraria montana var. lobata, started off in eastern Asia in primarily subtropical and temperate regions. The kudzu plant was introduced to the United States from Japan in 1876 at the Centennial Exposition in Philadelphia. The vine was widely marketed in the Southeast as an ornamental plant to be used to shade porches and later promoted as a forage crop (McGroarty, 2010). Concerns revolving around soil erosion through the 1930s and 1940s led the United States Department of Agriculture (USDA) to recommend the planting of Kudzu as a preventative measure along steep slopes throughout the south (Forseth & Innis, 2004). The Soil Erosion Service, a subsection of the USDA went on to provide approximately 85 million Kudzu seedlings to southern farmers, and paid them to plant the seedlings as a means to further prevent soil erosion throughout the Southern United States (Forseth & Innis, 2004; Grebner, Ezell, Prevost, & Gaddis, 2011). These activities were supplemented through a civilian corps movement that encouraged the planting of the vine in public lands and parks (Forseth & Innis, 2004). Due to governmental promotion, Kudzu had a solid hold throughout the Southeastern United States by the early 1950’s (Grebner et al., 2011). Even though Kudzu was removed from the list of permissible cover plants by 1953 (Grebner et al., 2011), declared a weed by 1970 (Hinman, 2011) and finally added to the noxious weeds list by 1997 (Grebner et al., 2011), the plant was able to spread throughout America and has made its way across the border into Canada. Kudzu is currently found on every continent with the exception of Antarctica (Gigon, Pron, & Buholzer, 2014 ).
In Canada, kudzu was discovered near Leamington, Ontario in 2009 and the population was estimated to be at least 8 years old at the time (Lindgren et al., 2013). It is not currently regulated as a pest under any legislation in Canada (Lindgren et al., 2013), nor does it have an official status as a noxious weed under the Weed Control Act (Waldron, 2012).
In the United States, kudzu has been able to quickly grow over and shade other vegetation, causing damage to crops, orchards, and forest plantations. The greatest monetary impact of kudzu growth has been felt by the forestry industry where the productivity losses of entire young forest plantations have been estimated between $100 million and $500 million per year (Lindgren et al., 2013). There is also concern that kudzu can host soybean rust (Phakopsora pachyrhizi), and crop damage and yield losses have been a problem for farmers (Lindgren et al., 2013). In the United States, kudzu has damaged power lines which costs power companies an estimated $1.5 million per year (Lindgren et al., 2013). Kudzu has also reportedly grown over rail lines and caused derailments, costing railroad companies a significant amount in control costs (Lindgren et al., 2013). Costs of control in national and state parks are also reported to be considerable (Lindgren et al., 2013).
Using climate suitability models of current and future climate conditions, it has been predicted that changes in the global climate will allow for kudzu to spread northward (Lindgren et al., 2013). Waldron (2012) believes that it is likely that the kudzu population near Leamington, Ontario will spread further into southern Ontario unless measures are taken to control it.
Kudzu is a specialized plant that will grow in certain conditions, thriving to unmanageable states if presented ideal conditions, and if found in locations where survivorship is low, could take years for seeds to germinate (Lindgren, C. J. et al). Kudzu’s ability to rapidly grow and take over a deciduous forest canopy stand can surpass any healthy forest ecosystem’s tree growth. It is possible for the vine to have multiple canopy layers that can total the entire biomass of a deciduous forest canopy (Forseth & Innis, 2004). Kudzu’s resilience to methods of eradication is strongly based on its large roots which store large amounts of starch, nitrogen, and water. The roots proficiency to grow into the substrate at 0.03 metres in depth a day, weighing over 180 kg and extending as deep as 3 metres is only one of many factors associated with the persistence of this plant (Forseth & Innis, 2004). This vine also has the ability to maneuver and redirect its leaf angles in relation to the direction of the sun; this is called paraheliotropism (Forseth & Innis, 2004). The leaves can be in positions to receive full sun, parallel to the sunrays to lower temperatures, and steep angles to prevent wilting (Lindgren et al., 2013). Kudzu’s adaptive qualities threaten local biodiversity through high competition for expanding room and below ground for roots. Studies have suggested that some of the common methods for controlling invasive vines, such as mowing, may be inadvertently causing the plants to grow back even more aggressively, which is something to consider when exploring management options (Kartzinel, Hamrick, Wang, Bowsher, Quigley, 2015). Kudzu is also a ‘structural parasite,’ meaning that, rather than supporting itself, it grows on top of other plants and buildings to reach light. Its ability to reproduce and spread quickly allows it to quickly cover shrubs, trees, and forests, where it blocks the sun’s rays from the plants below it, decreasing or eliminating their photosynthetic productivity (Miller & True, 1986).
CRITICAL ASSESSMENT OF MANAGEMENT OPTIONS
The invasion of kudzu has proven to be costly to many industries in North America. With Kudzu being relatively new to Canada, and currently limited to a single outbreak, there is still a high probability that an effective management strategy can be implemented to control and eventually eradicate the vine from Canadian Shores. Some of the management options include doing nothing, grazing, chemical control, biological control, prescribed burning, and mechanical removal. These options are considered and assessed based on costs, benefits, and additional factors. Each option is explored in the following paragraphs and compared in Table 1.
There is the option to do nothing, however, seeing as kudzu is predicted to expand its range, this is not recommended. Kudzu will continue to be a burden on many industries if management of the species is not addressed. It may, however, be viable to focus efforts in controlling kudzu by utilizing it rather than removing it. One of these control measures is grazing by livestock. If heavily grazed on for 3-4 growing seasons, the root systems starve and this may effectively eliminate a kudzu population (Starr et al. 1999). However, vines can grow over fences and up trees, rendering them inaccessible to livestock (Lindgren et al., 2013).
A method used to manage kudzu populations is an herbicide called Glyphosate. In Mississippi, Glyphosate was used to tame kudzu and was successful in controlling 60-85% of the vine after 4 years (Lindgren et al., 2013). In some other states, regular use of Glyphosate with a backpack sprayer saw results of 80-100% success in just one season of use. Although herbicides have been effective against kudzu, it requires multiple and frequent applications (Minogue, Enloe, Osiecka, Lauer, 2011). Studies have shown that kudzu that has been controlled with herbicides, and shows no signs of growth, can emerge from its roots after a year, possibly more, of dormancy (Minogue et al., 2011). Some herbicide treatments have left the soil bare, making it difficult to reestablish native species, and does not halt the return of kudzu as it has no problem growing in disturbed areas (Minogue et al., 2011). In some cases, herbaceous species have been able to colonize areas where kudzu has been reduced chemically, however kudzu can return and overtop these species in a single growing season if the area is not closely monitored (Minogue et al., 2011).
Another form of control is prescribed burning. This process kills the foliage of the plant but also requires repeated applications to be effective (Starr, Martz, Loope, 1999).
There are several biological means that are already in place and more that may be implemented to control the growth of kudzu. Bacterial blights, insect herbivory, and insect seed predation occur in high levels in field populations of kudzu. Seed predation is quite prevalent, with up to 81% of seeds incurring damage in populations studied in North Carolina. A study found two weevils that attacked the stems of kudzu and eight beetles that complete larval development in the kudzu roots. When evaluations of potential control agents are made, the range of the control agents must be considered. Efforts were made by the United States Forestry Service to find a biological control agent for kudzu. A “blackleg” fungus, a viral mosaic disease and a rust fungus have all been shown to cause mild injury to kudzu (Starr et al. 1999). Studies in China revealed that most of these biological control agents do not solely target kudzu, which is a risk to native species (Lindgren et al., 2013). More research needs to be done to determine the viability of biological control options.
Successful long term control of kudzu requires that the extensive root system be destroyed (Starr et al. 1999). As such, the mechanical removal of the entire root has proven to be effective in eradicating the species but is labour-intensive and time consuming (Starr et al. 1999). Another physical control method is close mowing but this requires frequent and repeated action (Starr et al. 1999). Close mowing has the same issues that grazing has as a control method because vines can grow up surfaces, which still requires alternative labour-intensive mechanical removal.
Table 1: Comparison of different potential management methods to deal with the invasive vine Kudzu. While time intensive, mechanical removal provides the greatest chance of success while reducing further negative impact on the environment.
Cowbrough, Mike. (2016) Photo: Canadian Kudzu population, Lake Erie.
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