Kudzu Defoliation

Although there is no controversy regarding the invasiveness of kudzu, recognition of the forage value of this species is still important. With the increasing cost of available approaches of kudzu control and the tremendous resilience of established populations, generating some returns from grazing at appropriate seasons and extents to deplete root reserves may allow greater progress in control of a continuing invasion. Currently available approaches to control, and eventually eradicate, this pest are largely based on the expensive repeated application of herbicides, cultivation, mechanical defoliation, grazing, or some combination of these treatments and possibly with facilitation of burning [Miller, 1996; Moorhead and Johnson, 1998; Everest et al., 1999]. Other than the more recent introduction of herbicides, these are the methods which were successfully used to keep kudzu under control on small farms across the southeastern states during the period of initial use of this plant as a shade, erosion control, and forage plant. Small diversified farms included interspersed cultivated fields and grazed pastures which held kudzu in check. As noted by Forseth and Innis [2004] the extensive planting of kudzu followed by widespread consolidation of farmlands and the associated concentration of the southern population in urban areas left countless small, widely distributed kudzu plantings essentially without limitations. Areas not subjected to cultivation or grazing, such as the extensive land areas allowed to develop as secondary forest, were not only readily accessible to any adjacent kudzu plants, but the spreading populations were not monitored and were essentially unnoticed in many instances. As a result, kudzu is now recognized as "perhaps the worst weed problem" in southeastern forests [Demers and Long, 2002]. Although urban and roadside populations were certainly noticed, their control was often neglected.

The need for caution with kudzu plantings was well understood early in the last century as illustrated by the advice of Duggar in 1925 that the plant should not be grown in gardens, along fence rows, on even "near" rich bottomland. The rapid growth and invasiveness of this plant have more recently been widely recognized [Hipps, 1994; Everest et al., 1999; Matlack, 2002]. Potential to drastically alter community structure and displace native vegetation are concerns for natural areas [Smith et al., 2001]. Physiological and ecological aspects of kudzu growth and development supporting this tremendous potential to spread across the landscape have recently been reviewed by Forseth and Innis [2004]. The particular combination of high allocation of photosynthate to extension growth, extensive rooting of vines at nodes, high leaf area indices with efficient light distribution to leaves within the canopy by paraheliotropic leaf movement, ability to fix atmospheric nitrogen, ability to overtop the tallest forest competitors using the structure of trees to reach full sunlight, and ability to exclude most competing plants from a site are some key characteristics contributing to vegetative expansion and dominance by existing populations [Forseth and Innis, 2004]. Tremendous root storage development over a period of years provides resilience under defoliation and, to some extent, resistance to herbicide treatment. Although natural spread by seed is likely very limited [Webster et al., 2006], hardseededness provides opportunity for soil seedbanks to contribute to re-establishment of stands as does root-crown dormancy induced by some effective herbicide treatments [Miller, 1996]. Thus repeated treatment, whether from herbicide, defoliation, or cultivation, and continued monitoring are required for elimination or even simply limitation of existing kudzu populations [Miller, 1996; Moorhead and Johnson, 1998; Everest et al., 1999]. On small scales, application of herbicide directly to remnants of individual plants as spot spray or even direct injection into individual root crowns following an initial defoliation has been recommended [Smith et al., 2001].

Efforts to eradicate kudzu have widely failed primarily due to either lack of appreciation of the continuing effort required and/or failure to recognize the re-colonization potential from population remnants beyond the boundary of the targeted area. The traditional control methods with greater temporal and spatial limitations than the target to be controlled continue to provide disappointing results. An evaluation of an integrated approach in forest establishment indicated that sustained kudzu control from a persistent herbicide could provide sufficient time for a dominant, smothering canopy of loblolly pine at high population density to develop and suppress the herbicide-weakened kudzu population [Harrington et al., 2003]. An appropriate, persistent herbicide with such a selective activity, however, is not available. As is suggested to contribute to natural limitation of this and other invasive plants in their native environments, biological control methods appear to hold promise [Britton et al., 2002]. Considerable progress has been made with evaluation of the fungus Myrothecuim verrucaria [Boyette et al., 2002], including development of a patented control process [Boyette et al., 2001]. Two insect species from China have also recently demonstrated potential [Frye et al., 2007]. These novel biological control approaches require considerable additional evaluation and verification of lack of non-target biological effects, particularly to the related and economically important soybean crop. Current populations in the southeastern U.S. are not without pests. Several insects and bacterial pathogens attack the foliage and seed of kudzu, but infestations do not occur at sufficient levels for control of the plant [Webster et al., 2006].

Grazing by domestic livestock represents an additional biological control approach which has proven potential as noted by recommendations for grazing management of kudzu pastures. As stated by Ball et al. [2002], "Continuous close grazing will weaken plants, reduce productivity, and eventually eliminate stands." Miller [1996] noted that "Close grazing for 3 to 4 years can eliminate kudzu when 80 percent or more of the vegetative growth is continuously consumed." Heavy grazing pressure in August and September each year were recognized as particularly effective for control by grazing defoliation [Miller, 1996]. Additional treatments such as dormant-season burning or mechanical methods may be required to remove vines from trees and other structures beyond reach of grazing livestock. Increased demand for goat meat in the region has contributed to interest in using goats for control of kudzu [Bonsi et al., 1992; Luginbuhl et al., 1996] with interest even in urban situations [Jonsson, 2003]. Miller [1996] noted, however, that grazing by cattle had demonstrated the most success at eradication of this plant. Requirements of grazing animals and their control, especially water and fencing, have been substantial limitations to use of this approach. Portable electric fence materials and relatively low-cost water transport equipment contribute to feasibility of this control approach in many situations. Even tethering and hand watering of individual animals may be useful approaches for small plant populations in some urban areas. Recognition of forage value of the plant in addition to grazing as an economical control method could contribute to development of viable grazing services for use and eventual elimination of existing populations in both extensive and localized urban situations.

Additional developments in rather wide ranging fields also have potential to contribute to the control of kudzu. Genetic variation and heterozygosity within populations have been reported at levels to indicate substantial sexual reproduction and selection for heterozygous individuals [Pappert et al., 2000]. Recent assessments of genetic diversity within southeastern U.S. populations indicate multiple introductions and subsequent gene exchange and recombination [Sun et al., 2005]. This information may be particularly useful in understanding responses to control efforts if variable responses among populations are encountered. Monitoring of responses to control efforts is particularly critical to treatment success. Remote sensing technology has shown promise as a useful means of monitoring populations of kudzu [Li et al., 2001].

In addition to developments with potential to aid in control and possibly eventual elimination of kudzu, additional changes now occurring contribute to an increased immediacy, if not actual urgency, for this control. The pathogen causing potentially devastating soybean rust has recently arrived in the region. The ability of this pathogen to over-winter on kudzu creates a substantial and immediate cause for concern [Frye et al., 2007]. In addition, evidence indicates that global warming and increased carbon dioxide concentrations will likely increase competitive ability of kudzu and extend its range to the north in the U.S. [Sasek and Strain, 1988, 1989, 1990; Forseth and Innis, 2004]. These increasing risks from the continuously expanding populations of kudzu are in addition to the already substantial economic losses particularly to forest enterprises, environmental degradation of natural areas, and safety concerns due to obstruction of visibility of traffic and other hazards.

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  • robyn
    Are there any local efforts for monoriting the population of kudzu?
    9 years ago

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