Lonicera japonica Thunb.

Origin and Introduction:

Lonicera tatarica is native to Central Asia and Southern Russia and is believed to have been introduced into North America for ornamental purposes as early as the 1750s.  Lonicera japonica, – a native of China, Japan and Korea – was introduced for horticultural purposes in 1806 on Long Island; it was widely distributed as a garden plant through the early-1900s when it was finally recognized as a weed.  Lonicera maackii, also native to China, Japan and Korea, was introduced as seeds to arboreta throughout the U.S. in the late-1800s to determine whether the plant would grow in North America. This species of honeysuckle was utilized as a soil stabilization and wildlife planning until the mid-1980s and is still available for sale on-line.  Lonicera morrowii, a native of Japan, was imported to Massachusetts in the 1860s and was later released as an ornamental. All four species have escaped cultivation and are easily spread by birds.

Identification:

Lonicera morrowii,  Lonicera tatarica, and  Lonicera maackii, are perennial shrubs;  Lonicera japonica is a perennial woody vine (although its leaves can remain green throughout mild winters). The shrub forms range from 6 to 15 feet in height, while vines can reach 30 feet in length. The egg-shaped leaves range from 1 to 3 inches in length and are arranged oppositely along stems. Invasive honeysuckles begin flowering from May to June and bear small (less than 1 inch long), very fragrant tubular flowers ranging from creamy white through various shades of pink to crimson. Lonicera morrowii and Lonicera tatarica produce ¼ inch red berries from mid-summer through early-fall; Lonicera maackii’s dark-red berries don’t ripen until late-fall; Lonicera japonica produces dark-purple or black berries in the fall. Stems of all four are hollow.

Impacts:  

All three species can form very dense populations that can outcompete and suppress the growth of native plant species. These dense stands suppress the growth of other native species. Lonicera maackii leafs out very early in spring, giving it a competitive advantage over native plants. Lonicera japonica leaves are semi-evergreen allowing the plant to grow longer into the winter and giving it a competitive advantage over native vegetation. It shades out understory growth preventing the success of native understory plants and tree seedlings. Its vigorous vine growth covers native trees; the weight of the vine growth can bring down weak trees. By decreasing light availability to the understory, these invasive honeysuckles can alter habitats by depleting soil moisture and nutrients. The invasive honeysuckle berries do not contain the amount of fat and nutrients present in native honeysuckle berries; eating large amounts of the less nutritious invasive berries rather than native berries can have negative impacts on migrating.

Prevention and Control:

Because these plants spread rapidly via birds eating seeds, control should be started in late-summer or early-fall before seeds are ready to be dispersed. In early stages of invasion, or in cases where populations are at low levels, hand removal of honeysuckle seedlings or young plants is a viable option when repeated annually. Systemic herbicides can be utilized in cases of heavy infestation. Specific state rules should be followed and the appropriate (low environment impact, legally labeled for control of these plants) herbicides should be used. For invasive honeysuckles growing in open habitats, prescribed burning may be an effective control alternative.

Habit: Climber

More info for the terms: competition, fire management, forbs, hardwood, invasive species, natural, presence, root crown, shrubs, vine, vines

Impacts: Japanese honeysuckle directly impacts native plants through competition for light [47,134] and soil resources [27,145]. Twining vines grow up and past small-diameter trees and shrubs, blocking sunlight with their dense canopy and eventually pulling down their dead hosts with the weight of the vine [47,56,74]. Twining Japanese honeysuckle vines may increase stem:leaf ratios of host plants, presumably because the extra weight exerted on the host plant requires greater stem support than would otherwise be required [35].

Japanese honeysuckle may also impact native communities by altering forest structure and species composition. Invasion of Japanese honeysuckle in eastern forests can lead to suppressed reproduction of  herbs and woody plants. Although the ground layer is most suppressed, plants of nearly all forest strata begin growth at the ground layer and are hence subject to suppression. Presence of Japanese honeysuckle and its effects upon understory regeneration could promote dramatic changes in forest structure. American elm (Ulmus americana), black cherry, and yellow-poplar on a Potomac River island in Washington D.C were particularly susceptible to suppressed regeneration due to shading from Japanese honeysuckle [134]. Japanese honeysuckle constrains oak regeneration in southeastern hardwood bottoms, especially following overstory thinning or removal [36,150,151]. It can also substantially inhibit pine regeneration in harvested stands when it is present prior to harvest. Presence of Japanese honeysuckle vines in harvestable stands may require substantial expense and effort to ensure pine regeneration [21,47,75].

Japanese honeysuckle retains photosynthetically active foliage during winter throughout much of its range. This trait, combined with ability to produce new leaves in early spring, enhances its competitive ability, and hence, its invasiveness. In many areas, Japanese honeysuckle can produce as much as 2 months of growth before most deciduous associates begin to grow. For example, in Maryland Japanese honeysuckle usually leafs out by mid-March, while the native oak forests are generally leafless until May [47,112]. However, Japanese honeysuckle becomes less invasive in northern portions of its eastern North American range due to a shorter growing season and frequent winter kill of accumulated stem growth [40,57,70]. In the arid western United States, Japanese honeysuckle is not likely to become widely invasive due to drought intolerance, especially of seedlings. However, it may persist in irrigated or riparian areas, becoming a localized pest [70].

Competitive ability and invasiveness of Japanese honeysuckle may be aided by its exceptional morphological plasticity. Japanese honeysuckle was compared with the native trumpet honeysuckle (Lonicera sempervirens), a sympatric, twining honeysuckle also found in the southeastern United States. Shoot growth of both species was examined with and without climbing supports. Japanese honeysuckle responded to the presence of climbing supports with a 15.3% decrease in internode length, a doubling of internode number, and a 43% increase in shoot biomass. In contrast, trumpet honeysuckle showed no influence of climbing supports on internode length or shoot biomass, and only a 25% increase in internode number [115].

Another trait that may enable Japanese honeysuckle's invasiveness is its ability to spread rapidly by both vegetative and sexual means. It readily sprouts from the root crown, especially in response to stem damage. Additionally, new individuals are established when plants put down roots at nodes along stems, forming new root crowns and spawning new plants. Heavy fruit-bearing colonies can rapidly disperse seed throughout a wide area by attracting frugivorous birds [47].

While Japanese honeysuckle was promoted and planted as a beneficial wildlife species in the eastern United States during the mid 1900s, emphasis has now changed toward controlling its spread [57]. Japanese honeysuckle does provide food for wildlife, but it also suppresses many native plants that may be of greater economic or ecological value [47].

Japanese honeysuckle is one of several invasive exotic plant species considered a "significant management concern" in Shenandoah National Park, Virginia, and is a "widely reported problem species" in federal wilderness areas in Alabama, Arkansas, and Kentucky [72]. Japanese honeysuckle may threaten the rare Trillium pusillum in southern Tennessee, a state endangered plant. Japanese honeysuckle impacts native forest forbs by outcompeting them for light following release due to opening of canopy gaps [30].

Japanese honeysuckle is an important early and late-season host for the important agricultural pests tobacco budworm and corn earworm in southern Georgia and northern Florida [91].

Control: Controlling Japanese honeysuckle may require determined, protracted effort. Because it readily sprouts in response to cambium damage, single treatments are unlikely to eradicate established plants. Persistence of invasive Japanese honeysuckle will vary with site, duration of establishment, and control methods employed, and may be difficult to predict.

In areas where invasive Japanese honeysuckle suppresses populations of rare native plant species, control efforts may require careful consideration. While control efforts may be motivated by conservation objectives, treatments such as herbicide application or prescribed burning could have adverse effects on threatened or endangered species [30].

Prevention: Because Japanese honeysuckle seed may be widely dispersed by birds and other animals, periodic monitoring of susceptible habitats, and subsequent removal of detected invaders, can prevent establishment of dense, intractable colonies. The semi-evergreen nature of Japanese honeysuckle may present a competitive advantage over native deciduous plants, but it does allow easier detection of invasive populations during winter [90].

Integrated management: Integrated management represents a systems approach to control of invasive species. It typically involves a variety of control methods, often used in combination, with the choice, sequence, and timing of treatments chosen to minimize the target's weaknesses while maximizing control effectiveness. Integrated management calls for detailed understanding of the ecology and life history of the target species, as well as the desired native community, and relies on planning, monitoring and data-gathering [31]. The control methods outlined in this section provide information relevant to developing integrated management strategies for controlling Japanese honeysuckle in North America. Evans and Heitlinger [31] provide a detailed review of integrated management in natural areas.

Physical/mechanical:  Mechanical treatments can suppress invasive Japanese honeysuckle, but plants will sprout in response to cambium damage. Mechanical control is likely to be effective only if it is perpetuated for a relatively long time, or if temporary suppression is the goal. In open areas, Japanese honeysuckle may be controlled by repeated mowing [30]. Mowing reduces the spread of vegetative stems but may not completely eradicate entire populations. Mowing reduces average stem length, but increases numbers of genets [90]. At an Arkansas timber harvest site where invasive vines were present prior to harvest, disking provided suppression of Japanese honeysuckle sufficient to ensure natural regeneration of loblolly pine seedlings. "Bushhogging" was not an effective site preparation for natural pine regeneration, but planted seedlings were able to establish and compete after 2 years [75]. Combining mechanical treatments with 1 or more additional methods such as prescribed burning or herbicides may enhance effectiveness, but there are no published accounts of such efforts.

Hand-pulling mature plants is difficult due to extensive root systems, but seedlings (< 2 years old) can be eradicated in this manner [30]. Hand-pulling at an old field site in southwestern Indiana resulted in good control of Japanese honeysuckle and release of many native forbs and grasses, but was very labor-intensive [93].

Fire: See Fire Management Considerations.

Biological: No information

Grazing/Browsing: Browsing livestock can reduce Japanese honeysuckle vegetative growth, especially over multiple seasons. Browsing is unlikely to provide complete eradication [17,90].

Chemical: Herbicides may control Japanese honeysuckle, especially when used in combination with other methods. It is unlikely that Japanese honeysuckle can be eliminated with a single herbicide treatment [22,99,100]. Spot application of herbicides may be effective as a follow-up to prescribed burning, which can substantially reduce aboveground biomass (see Fire Management Considerations) [90].

Some research indicates that herbicide application prior to the first hard freeze (25 degrees Fahrenheit (-3.9 ºC)) is most effective [90], while other studies indicate delaying treatment until early winter may still be effective with some chemicals [104]. Because Japanese honeysuckle retains its leaves during the dormant season of most native deciduous plants, spraying foliar-absorbed herbicides during this period reduces off-target effects [90]. Care should be taken when using chemicals that may harm nontarget plants, since these plants will be important in recolonizing the site after Japanese honeysuckle is controlled [90,93].

Below is a list of herbicides that have been tested and judged effective for controlling Japanese honeysuckle in North America. 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 Japanese honeysuckle, see Illinois Nature Preserves' Vegetation Management Guideline and The Nature Conservancy's Element Stewardship Abstract web pages.

Picloram [99]
Hexazinone [77]
Glyphosate [74,90,104,113]
Amitrole [74,152]
Metsulfuron [36,150]
Triclopyr + 2,4-D [90]

Cultural: No information

Japanese honeysuckle occurs across the southern U.S. from California to New England and the Great Lakes region. Escaped populations also occur in Hawaii. Severe winter temperatures and low precipitation may limit its distribution in northern latitudes and in the West, respectively.