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 Oriental Bittersweet 

Oriental bittersweet (scientific name Celastrus orbiculatus) is a deciduous woody vine that is native to eastern Asia. It was brought to the United States in the late 1800s for use as decorative ornamentals, and its bright yellow and red-orange fruits give it a unique look that continues its popularity as an ornamental plant to be cultivated. Oriental bittersweet is a perennial, woody vine that can grow up to 60 feet in height as well as growing in low-to-the-ground, dense patches. It grows well in both full sun and partial shade, and

can establish itself in a wide variety of soil types and textures, including clay, sandy, loamy, and rocky soils, as well as in high soils that are high in organic matter. It prefers moist soils, and can live in acidic, neutral, and alkaline ranges of soil pH. This ability to thrive in this varying range of environments makes the spread of oriental bittersweet prolific. 

The leaves of oriental bittersweet are about 3 to 6 inches long and about 1 to 3 inches wide, and appear glossy and broad with rounded tips with an alternate growth pattern on the vines. The leaves will appear as an olive green color in the spring and summer, while they turn yellow in the fall. Oriental bittersweet consists of separate flowering (female) and non-fruiting (male) plants. Flowers appear during the late spring and early summer, between May and June, and they appear in clusters of small (less than 1 inch), white-green star shaped flowers sprouting from the leaf axils. The bark of oriental bittersweet appears in either a red/burgundy, or dark brown color,  and is dotted with whitish, corky spots called lenticels, which are raised pores that facilitate gas exchange in woody plants. Stems on the woody vine also contain these lenticels, and as the plant matures, the bark grows rougher in appearance and texture. Fruits that appear on the female plants begin to ripen on the vine throughout August and September, turning from green to yellow before the fruit splits in the winter, revealing red-orange interiors that look very similar to berries. 

Oftentimes, oriental bittersweet is confused with our native bittersweet called climbing bittersweet or American bittersweet (c. scandens). You can tell these two species apart by looking closely at the leaves. Oriental bittersweet’s leaf tips will be rounded, where the native American bittersweet’s leaves will taper to a point at the tip. Another difference that can be used to determine whether you are seeing the American or Oriental bittersweet vine is by looking at the fruit if you have a fruiting plant on your property. The invasive (oriental bittersweet) variety usually produces fruit of a brighter red color, and forms in clusters of 3 to 7 fruits all along the length of the stems. The native (American bittersweet) variety produces much larger clusters of fruit, and the fruits will only appear at the tips of the stems. Unfortunately, there is a chance of crossbreeding between the invasive and native species, which endangers the native species by removing its genetic identity, and making them even more difficult to distinguish from one another.

How it Spreads

Oriental bittersweet has many properties that make it a prolific spreader throughout a variety of ecosystems. As mentioned before, it can thrive in many different soil types and textures, and is tolerant of both full sun and partial shade. It produces seeds in large numbers, which are eaten by a variety of wildlife, mainly large numbers of birds. Because of their inclusion in the diets of these creatures, this invasive plant has the potential for a very wide dispersal range. The seeds of oriental bittersweet also have up to a 95% success rate of seed germination, with the highest rates of germination in areas of lower light intensities, such as under thick forest canopies. This invasive plant species has developed a strategy of remaining dormant until the soil around it is disturbed, which creates conditions for the oriental bittersweet to take root and grow rapidly. Similarly to many other non-native invasive plant species, oriental bittersweet’s roots are rhizomal, meaning they contain underground stems that allow for the spread of dense patches of the plant. As mentioned before, this invasive species can also hybridize with native American bittersweet species, destroying the native population as well as helping the spread of the invasive oriental bittersweet. 

Oriental bittersweet is often spotted around old homesites throughout North Carolina, where it has escaped into forested areas around those sites. It is also seen in fields, hedgerows, forest edges, roadsides, and disturbed woodlands, and has begun to spread from the mountainous region of NC and into the piedmont. It is an aggressive vine in its method of spreading, climbing up trees and strangling them through girdling, preventing photosynthesis, and even making trees more likely to uproot from the excess weight that the oriental bittersweet adds. 

Controlling Oriental Bittersweet

The first step to controlling oriental bittersweet is identifying it in undisturbed areas before the soil is disturbed and the invasive vine begins to grow rapidly. If you can identify these areas before they explode into infestations, then it is possible to dig and hand-pull these small initial populations. If you are attempting to hand-pull oriental bittersweet, you must ensure that you remove the entire root system, or the plant will resprout. Once you have pulled oriental bittersweet, bag all plant material from the removed invasive, and dispose of it in the trash in the bag. 

For low, dense patches of oriental bittersweet, a successful method of control is to cut the vegetation down early in the growing season (usually in April), and then allow it to grow back for about one month. After that month period of time, spray a 2% application of triclopyr to the foliage. In instances where the vines have grown up into the tree canopy, cut the stem of the vine 2 inches above the ground, and then immediately spray a 50% triclopyr solution onto the cut stem. 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. This cut-stump method, as it is known, is effective as long as the ground is not frozen, so it may be best to avoid using this method of control during the winter months. 

No matter which method of control you choose to combat oriental bittersweet, 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 oriental bittersweet, please contact the Madison County Cooperative Extension Center at peyton_duckett@ncsu.edu, or (828) 649-2411. 

Citations

Fryer, Janet L. (2011). Celastrus Orbiculatus. Fire Effects Information Systems (FEIS). USDA, & US Forest Service. https://www.fs.usda.gov/database/feis/plants/vine/celorb/all.html. 

NCDOT, & NC Forest Service. (2010, March). Celastrus Orbiculatus (Oriental Bittersweet). Invasive Species Leaflet. https://www.ncagr.gov/divisions/nc-forest-service/is07/download?attachment.

NC State Extension. (n.d.). Celastrus Orbiculatos. North Carolina Extension Gardener Plant Toolbox. https://plants.ces.ncsu.edu/plants/celastrus-orbiculatus/.