Invasive in the Spotlight: Japanese Honeysuckle
Japanese honeysuckle (Lonicera japonica) is a woody, vining evergreen (or semi-evergreen) plant with attractive, fragrant white flowers that fade to yellow in the spring and produce black berries in the fall. Its leaves are opposite, with visible petioles (leaf stems). Older stems are hollow and can reach up to 120’ in length! Its older bark peels in long strips. It is most commonly found in “edge” habitats but will also colonize gaps in the forest.
It is unclear when Japanese honeysuckle was first introduced as an ornamental plant to North America, but it was well over 100 years ago. Since then, it has escaped cultivation and is now found throughout most of the United States. Not all states recognize the plant as a noxious weed, but New Hampshire treats it as a prohibited invasive species, and as such, it should never be sold, planted, or propagated.
As is the case with most invasive plants, Japanese honeysuckle threatens to out-compete and displace native species. It will readily climb and shade out other plants, as well as sprawl along the ground. It can become so heavy it will topple its host plant. Besides seed dispersal by birds, Japanese honeysuckle can reproduce vegetatively (with both rhizomes and runners). Like many invasive plants, it has few natural enemies or competitors to keep its growth in check.
Although you’re unlikely to find this prohibited plant for sale at a garden center, it is possible that well-meaning but under-informed gardeners will offer it at plant sales or swaps. Do not plant any honeysuckle unless you are sure it is not an invasive variety.
Using an Integrated Pest Management (IPM) approach, use mechanical means first, such as digging out or pulling the vines by their roots. This method works best for small populations.
If mechanical control isn’t possible or practical, such as with large infestations, Japanese honeysuckle can be managed with herbicides such as glyphosate or triclopyr. If applying as a foliar spray, these herbicides are best applied in fall or early spring while native vegetation is still dormant. These herbicides should be applied according to product label instructions.
Ironically, another honeysuckle species is the best alternative to L. japonica: coral or trumpet honeysuckle (L. sempervirens). This plant is every bit as attractive as Japanese Honeysuckle, and several cultivars are available. In its native form, it can be distinguished by its scarlet flowers with yellow interiors, red berries (as opposed to black), and leaves that surround the stems without noticeable petioles. Though the flowers are not fragrant, it is a favorite of hummingbirds.
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