Japanese Honeysuckle Control
Japanese honeysuckle is a semi-evergreen vine in Missouri, often holding its leaves late into winter. Leaves are ovate and 1.5 to 3.2 inches (4 to 8 cm) long. White to yellow tubular flowers form in pairs in the leaf axils from May-June. The 2 to 3 seeded fruits are small (5 to 6 mm long) and black.
Japanese honeysuckle is separated easily from the native honeysuckle vines by its leaves. Leaves near tips of the vines of Japanese honeysuckle are opposite and not united, while leaves of native honeysuckles (three species) are united at the base, forming a single leaf surrounding the stem. Trumpet or coral honeysuckle is another non-native vine that occasionally escapes from cultivation in the Midwest, but it is not an aggressive species. The leaves near the tips of the vine of trumpet honeysuckle are united at the base as in our native species. It may be distinguished from the native vines as well as from Japanese honeysuckle by its red flowers. Japanese honeysuckle should be accurately identified before attempting any control measures. If identification of the species is in doubt, the plant's identity should be confirmed by a knowledgeable individual and/or by consulting appropriate books.
Japanese honeysuckle is native to Japan, introduced to the U.S. in 1806 for horticultural ground-cover purposes. It was slow to escape and did not become widely established over the eastern U.S. until the early 1900s. It presently occurs as far north as Illinois and Michigan, from Texas to Florida, and north to Massachusetts, New York and Ohio. In Missouri, the species is most abundant in the southeastern counties, but it occurs sporadically throughout most of the rest of the state. Bitter winter temperatures appear to limit its establishment.
Japanese honeysuckle readily invades open natural communities, often by seed spread by birds. An aggressive colonizer of successional fields, this vine also will invade mature forest and open woodlands such as post oak flatwoods and pin oak flatwoods. Forests with either natural or unnatural openings are often invaded by Japanese honeysuckle when birds drop seeds into these light gap areas.
Old homesites frequently harbor Japanese honeysuckle and provide a seed source for spread into the surrounding landscape. Deep shading reduces the amount of invasion.
Japanese honeysuckle climbs and drapes over native vegetation, shading it out. It is capable of completely covering herbaceous and understory plants, and climbing trees to the canopy. The semi-evergreen condition of this honeysuckle allows for growth both prior to and after dormancy of other deciduous plants. The prolific growth covers and smothers vegetation present including understory shrubs and trees in forested communities. Although this prolonged growth period is beneficial to the plant, it is also beneficial in controlling the plant. Vegetative runners are most prolific in the open sun and will resprout where touching the soil, forming mats of new plants. This honeysuckle will display little growth under moderate shade. In deep shade, runners develop but often die back. Flowering and seed development are heaviest in open-sun areas. Seedling establishment and growth is slow in the first two years of development of a new honeysuckle colony.
Effect Upon Natural Areas
This aggressive vine seriously alters or destroys the understory and herbaceous layers of the communities it invades, including prairies, barrens, glades, flatwoods, savannas, floodplain and upland forests. It may become established in forested natural areas when openings are created from treefalls or when natural features allow a greater light intensity in the understory. Japanese honeysuckle also may alter understory bird populations in forest communities.
Missouri natural areas in the Crowley's Ridge area have suffered from Japanese honeysuckle invasion. The species is well established at numerous other Missouri sites and will surely be a continuing problem for land managers.
Initial effort in areas of heavy and light infestation
Efforts to control Japanese honeysuckle infestations have included the following methods: mowing, grazing, prescribed burning and herbicides. While grazing and mowing reduce the spread of vegetative stems, prescribed burns or a combination of prescribed burns and herbicide spraying appears to be the best way to eradicate this vine.
In fire-adapted communities, spring prescribed burns greatly reduced Japanese honeysuckle coverage and crown volume. Repeated fires reduced honeysuckle by as much as 50 percent over a single burn. A previously burned population of honeysuckle will recover after several years if fire is excluded during this time. By reducing honeysuckle coverage with fire, refined herbicide treatments may be applied, if considered necessary, using less chemical. Because Japanese honeysuckle is semi-evergreen, it will continue to photosynthesize after surrounding deciduous vegetation is dormant. This condition allows managers to detect the amount of infestation, and allows for treatment of the infestation with herbicides without damage to the dormant vegetation.
Glyphosate herbicide (tradename Roundup) is the recommended treatment for this honeysuckle. A 1.5- to 2-percent solution (2 to 2.6 ounces of Roundup/gallon water) applied as a spray to the foliage will effectively eradicate Japanese honeysuckle. The herbicide should be applied after surrounding vegetation has become dormant in autumn but before a hard freeze (25 degrees F). Roundup should be applied carefully by hand sprayer, and spray coverage should be uniform and complete. Do not spray so heavily that the herbicide drips off the target species. Retreatment may be necessary for plants that are missed because of dense growth. Although glyphosate is effective when used during the growing season, use at this time is not recommended in natural areas because of the potential harm to nontarget plants. Foliar application of herbicides will be less effective prior to early summer (July 4) because early season shoot elongation will limit the transfer of chemical to the root system. Glyphosate is non-selective, so care should be taken to avoid contacting nontarget species. Nontarget plants will be important in recolonizing the site after Japanese honeysuckle is controlled. Crossbow, a formulation of triclopyr and 2,4-D, is also a very effective herbicide that controls Japanese honeysuckle. Crossbow should be mixed according to label instructions for foliar application and applied as a foliar spray. It may be applied at dormant periods, like glyphosate, and precautions given above for glyphosate should be followed when using Crossbow. Either herbicide should be applied while backing away from the treated area to avoid walking through the wet herbicide. Garlon 3A and Garlon 4 (triclopyr) are also effective in foliar applications. By law, herbicides only may be applied according to label instructions and by licensed herbicide applicators or operators when working on public properties.
Mechanical cutting of aerial vines, followed by cut-surface herbicide treatment can be effective and minimizes the risk of spray drift. Undiluted Garlon 4 or a 20-percent solution of Roundup should be applied to cut stems immediately following cutting.
In fire-adapted communities, periodic spring burning should control this species.
Failed or Ineffective Practices
Mowing limits the length of Japanese honeysuckle vines, but will increase the number of stems produced.
Grazing may have the same effects as mowing, but is less predictable due to uneven treatment given by browsing animals.
Herbicides that have given poor control results or that are more persistent in the environment than other types are picloram, annitrole, aminotriazole, atrazine, dicamba, dicamba 2,4-D, 2,4-D, DPX 5648, fenac, fenuron, simazine triclopyr.