There are a wide variety of non-native invasive plant species that have taken hold in Madison County. These plants cause harm to the environment, as well as potential harm to human, animal, and plant health in the preexisting environment. Some of these damages can be caused by overtaking beneficial native plants in the ecosystem, act as vectors for diseases and other invasive species, such as invasive insects, and are unhealthy or potentially toxic to native animals. In this series, we will discuss identification and control of these prevalent invasive plants.
Identifying Japanese Honeysuckle
Japanese honeysuckle (scientific name Lonicera japonica) is a perennial vine that is native to many parts of East Asia. It is fast growing, and throughout North Carolina is considered an evergreen or semi-evergreen plant with two different potential growth patterns. This vine can grow in a pattern of climbing or twisting up shrubs and trees into the canopy of the natural areas it has infiltrated, or it can crawl along the forest floor, creating a thick groundcover. This invasive plant is also known for growing very quickly, and can reach sizes of 16 to 29 feet high and 3 to 6 feet wide. When the plant is young, the stems are slender, but as the plant matures these stems become hollow and can be up to 2 inches in diameter with brownish bark that can be easily peeled in long strips. The leaves are oblong or oval shaped and about 1 to 2 ½ inches long, but can vary in detailed shapes depending on if the plant is young or matured. Oftentimes, the leaves on young Japanese honeysuckle are lobed, meaning they will have distinct areas poking off the central shape, while the leaves of mature Japanese honeysuckle are smooth.
The flowers are the most distinguishing feature of this invasive plant. The flowers of Japanese honeysuckle usually range from about 1 inch in size, and can be white or pale yellow in color. They are irregularly trumpet-shaped with 4 to 5 petals, and are extremely fragrant. These flowers begin to bloom in late April, and continue to bloom through August, about the time that the plant begins to produce fruits. The fruits of this invasive plant appear in the late summer and through the fall, and are black, small, and spherical berries less than an inch in size. These small black fruits are toxic if ingested in large quantities, which can cause symptoms such as vomiting, diarrhea, rapid heartbeat, convulsions, and respiratory failure among others. This invasive plant can thrive in both full sun and partial shade, as well as a variety of soil types and conditions, such as sandy, silty, or clay soils, and acidic, basic, or neutral soils. You can view photos of Japanese honeysuckle through the NC Extension Gardener Plant Toolbox here.
There are some traits that can be used to distinguish this invasive honeysuckle from the three native honeysuckle species we have here in North Carolina. Firstly, and the most obvious trait to differentiate the native species from the invasive honeysuckle is the color of the fruits. The native species will have fruits of red or orange colors rather than the black fruits visible on Japanese honeysuckle. Another trait that can help determine the difference between the native and invasive honeysuckles are in the shapes of their leaves. The leaves of native honeysuckle are an oval shape, but rather than growing off of the stems, these leaves actually form around the stems. Lastly, some of these native honeysuckle species actually produce golden orange, or red, trumpet shaped flowers rather than white or light yellow like Japanese honeysuckle. Images of these differences can be found using the link here, showing native honeysuckle plants.
How it Spreads
Japanese honeysuckle spreads quickly throughout the environment using a few different methods. Like many other invasive plant species, invasive honeysuckle spreads through rhizomes within its root system. These rhizomes are underground stems connected to the root systems, which can allow the plant to form dense thickets that choke out other, native and more ecologically beneficial ground cover. Also contributing to its rapid growth and ability to take over, it creates runners along the stems and leaf junction areas of the vines, known as nodes, that allow the plants to form new roots in the ground and continue to crawl and spread. These runners also contribute to the formation of thickets throughout the forests and fields and other invaded areas. Birds and other wildlife eating the small fruits produced by this invasive plant also contribute to a wider range of spread into previously uninfested areas, but these fruits are only produced on flowering plants in higher light condition areas. Most often, these dense infestations of Japanese honeysuckle appear in disturbed areas, like right-of-ways, the edges of forests, and fields. When growing as vines, this invasive plant can grow both vertically and horizontally, climbing up small trees and shrubs as well as along the forest floor. When these vines climb over these small trees, they can damage native or more beneficial plants by girdling them as they continue to grow, or by blocking out the sunlight from the other plants that they have overgrown, essentially starving them by preventing photosynthesis.
Controlling Japanese Honeysuckle
There are a few possible methods of controlling Japanese honeysuckle, including both mechanical and chemical controls. Mechanical methods include manual removal of plant material, such as mowing, weed-eating, or pulling. Small infestations of this invasive plant can be removed by hand-pulling, but care must be taken to remove any plants from the area once they are pulled, including any mature fruits, to help prevent resprouting. After the initial removal of the honeysuckle from the area, the invaded space will need to be continuously monitored to remove any potential resprouts as they come back up.
Chemical controls, usually involving the use of herbicides, is often necessary to the control of larger infestations of Japanese honeysuckle, and will often require the use of different application methods to be most successful. These two different application methods are known as a foliar application, and a cut-stump application. The cut-stump application is a more targeted method used to remove vining honeysuckle plants, and is executed by cutting the vine of the honeysuckle plant within two inches of the ground, and then immediately spraying that newly formed stump with a 25% solution of triclopyr. You must apply the pesticide as quickly as possible to the stem to allow for the turgor pressure of the plant’s vascular system to absorb it into the root system. Turgor pressure is caused by the pressure of water within the plant cells that allows the plant to keep its upright and rigid structure, as well as aiding in the flow of nutrients across the expanse of the plant, from the tips of the leaves to the ends of the roots underground. The cut-stump method can be used any time of year for effective use, as long as the ground is not frozen. Once the stump has been sprayed, remove the upper parts of the vine from the trees to prevent girdling.
A foliar application to control Japanese honeysuckle works most effectively on the thickets or groundcover areas that have been infested. This application can be done with a solution of about 2 percent triclopyr plus 0.5 percent of a non-ionic surfactant to help aid the herbicide in being most effective. Thoroughly wet all leaves with the herbicide solution to ensure that the invasive plant will be exposed to enough of the herbicide for it to be effective. This application method can also be effective any time of year, as long as there is healthy green foliage on the plant, and the temperature is above 55 to 60 degrees Fahrenheit for several days.
No matter which method of control you choose to combat Japanese honeysuckle, be sure to follow up the next year to monitor and control any new sprouts and seedlings that have begun to make themselves known. If you choose to use pesticides, please be sure to use them according to the label. The label is the law!
If you have any other questions about identifying or controlling Japanese honeysuckle, please contact the Madison County Cooperative Extension Center at peyton_duckett@ncsu.edu, or (828) 649-2411.
Citations
NC State Extension. (n.d.). Lonicera japonica. North Carolina Extension Gardener
Plant Toolbox. https://plants.ces.ncsu.edu/plants/lonicera-japonica/.
NCDOT, & NC Forest Service. (2010, March). Lonicera japonica (Japanese
Honeysuckle). Invasive Species Leaflet.
https://www.ncagr.gov/divisions/nc-forest-service/is09/download?attachment.
