Oriental bittersweet (Celastrus orbiculatus) is a woody vine that belongs to the Celastraceae family. It is also known as Chinese bittersweet, Asiatic bittersweet, Asian bittersweet or Chinese bittersweet. Native to China, Japan, and Korea, it was introduced into the U.S. soils around 1879. It closely resembles the American bittersweet which is a native plant species. This plant is considered an invasive weed in the U.S. and in this article we will talk about how to control oriental bittersweet in your yard.
How to identify Oriental bittersweet
Oriental bittersweet is a woody twining vine that grows up to a height of 100 ft (30 meters) if left undisturbed. Mostly they are thin and usually silver to reddish-brown. The vine can grow up to the age of 20 years. The weed chokes the host plant to death.
Oriental bittersweet can also break the branches of the host tree because of its weight. It is also deciduous and has a deep and well-formed root system. Oriental bittersweet climbs by coiling around trees, shrubs and any available support.
This weed has alternating leaves that are fine-toothed and glossy. They are usually round but sometimes the shapes of the leaves may vary. The leaves usually turn yellow in fall and retain their green color late in the season. Its stems are usually light brown with white pith. The stems also have conspicuous horizontal marks. Oriental bittersweet has orange roots.
Oriental bittersweet leaves and flowers
The weed produces small five-petal flowers that are greenish to yellow. They usually bloom around May and June. The plant produces seeds that are brightly colored. They are usually yellowish-orange and disperse in autumn. All parts of the oriental bittersweet are poisonous.
The plant has a male and female plant growing separately. These plants then produce male and female flowers respectively at the age of two years. This does not rule out the possibility of having both a male and a female flower.
Once the flower matures, it produces seeds which are usually dispersed by birds and small mammals. The seeds are nutritious to birds, this makes long-distance dispersion easy. The seeds can also be dispersed by humans. This is done when it is planted as an ornamental plant and starts producing seeds.
Natural habitat of Oriental bittersweet
Oriental bittersweet usually thrives around grasslands, woodlands, roadsides, closed-canopy forests and fence rows. It is also becoming a problem in some beaches and dunes across the U.S. The weed grows faster in full sunlight. However, the seeds can still germinate in low light.
Reports of oriental bittersweet in the US
Why is Oriental bittersweet invasive?
Oriental bittersweet grows rapidly posing a threat to native plant species. It girdles the native plants and embeds itself onto the plants. The weed then siphons water and nutrients from the host plant.
The weed is an aggressive plant which poses danger to the native plant community. Its brightly colored fruits and seeds usually attract insects and small mammals. They eat the seeds and then excrete it elsewhere which made the plant spread faster. The weed also grows where there is dense vegetation which means it chooses areas with the most nutrients to exploit.
Oriental bittersweet uses multiple invasion and dispersal techniques which allow it to out-compete other plants. It is also a difficult weed to control. Its spread has led to imbalance in the ecology as well as in the agricultural land. These have made it a focus of environmental conservation efforts.
Factors that make the weed an aggressive competitor:
Response to abiotic factors
Oriental bittersweet likes places that are high and steep. Sunlight, nitrogen and optimum temperature are the main ingredients for the growth of the plant. Studies have been conducted on the resilience of the plant under unfavorable conditions. The plant showed resilience in all the unfavorable conditions that it was exposed to.
Sunlight is a key resource for the growth of this plant. This is clearly shown by the controlled experiments done using this plant. The plant showed tremendous growth when exposed to enough sunshine. It also showed resilience when exposed to reduced sunlight with a very low mortality rate.
This is not the case with its compatriot, the American bittersweet. The American bittersweet exhibited a high mortality rate when exposed to reduced sunlight. The Oriental bittersweet also had superior height and was also superior in attaining light.
High temperatures have been found to inhibit the growth of other invasive plants. This is not the case with the Oriental bittersweet. Studies have shown that the plant also thrives in areas with high summer temperatures.
Biotic interactions
Studies have shown that the plant forms a mutualistic relationship with arbuscular mycorrhizal fungi. The fungus helps it in the absorption of phosphorus and other crucial nutrients from the soil. This makes the plant to effectively invade an ecosystem in an area without necessary developing its root system.
This makes the plant to focus its energy on the upper biomass and make it bigger, and more aggressive than its competitors. The plant also disrupts the ecological balance in the area, it does this by altering the symbiotic relationships existing in the soil.
Hybridization
Hybridization usually happens between the female American bittersweet and the male Oriental bittersweet. This leads to a new plant that inherits the invasive properties of the plant. Since the Oriental bittersweet spreads aggressively, it has the potential to render the American bittersweet extinct.
How to control Oriental bittersweet
This invasive plant needs elaborate control plans, the plant’s growth and dispersal must be closely monitored. Early detection of oriental bittersweet can also go a long way to ensure the successful elimination of the plant. Stopping its destruction of the trees and shrubs is also paramount.
Because oriental bittersweet is capable of being dispersed over a long distance by birds, it is important to monitor the adjacent lands for parent plants. The landowners are usually advised to inspect land up to a mile/kilometer away from the management site.
Different methods can be used to control oriental bittersweet. The use of chemicals and mechanical methods are most effective in controlling oriental bittersweet.
Mechanical control
These are the physical methods used to eradicate oriental bittersweet. They are usually aimed at injuring, killing or inhibiting the growth of the weed. These methods are labor-intensive and only effective where there is a small infestation by the weed. They work better when supplemented by other methods such as the use of chemicals.
Hand-pulling/Digging
This method is usually not effective for established Oriental bittersweet plants. The roots move horizontally on the ground and cover long distances. This may cause difficulty in pulling the roots from the soil. It may be difficult to uproot the plant from some soils. The method requires repeated hand pulling to achieve a meaningful result. This requires commitment and frequent follow up to successfully control oriental bittersweet.
The best time to remove the oriental bittersweet from the soil is when the soil is moist.
Where the infestation is small but the plants are big, digging is required. Oriental bittersweet also grows shoots from the already established root system. Afterward, during routine monitoring, the seedlings can be hand-pulled from the ground.
Cutting/ mowing
Cutting the plant is not an effective method. This is because the oriental bittersweet always sprouts after the cutting. However, this method is used to minimize the destructive effects the weed has on other plants. This is usually a short term control method because soon after, the plant grows again. Cutting the stems leaves the vines in the canopy without nutrients. This causes the vines to dry off and die in two or three years.
Mowing also causes the plant to sprout. However, if it is repeated weekly it can be an effective control method. Mowing repeatedly depletes the plant’s energy reserves. This reduces its infestation in an area. Mowing sparingly throughout the season usually accelerates the infestation process. This is because it encourages the roots to sprout back and also aids in the dispersion of the seeds.
Prescribed burning
This method can be used in areas where the native plants have fire resilience. It helps in controlling large vines and reduces seed production of the plant in the canopy. It is, however, effective if it is accompanied by the use of herbicides.
Burning can lead to increased growth of the invasive plant if not used effectively. This is because it encourages the root sprouting of the plant. The vines can also cause forest fires, as they can act as ladders to the forest canopies.
Chemical control
This is the most effective control method for established oriental bittersweet infestations. Caution should be taken so that the desired plants are not destroyed. The application should also be done by a professional or someone who is competent enough. Additives such as dyes, penetrating oils, surfactants, and agents are used. Dyes are usually used to mark the plants already sprayed.
Herbicides containing glyphosate and triclopyr are used to control oriental bittersweet. Glyphosate can be used as a foliar spray or for cut surface treatment. It is effective when the leaves are fully formed and are growing actively.
It should not be used in the spring when the leaves of the plants are beginning to form. Glyphosate is a non-discriminate herbicide that kills any plant that it comes into contact with. It requires expertise in spraying so that damage is not done to the non-target native plants.
Herbicides containing triclopyr are recommended because they do not kill nontarget plants. Some experts argue that it is more effective in killing the roots than glyphosate. The herbicide is effective in controlling the weed because it persists until the plant dies. It can be used as a foliar spray as well as in conjunction with the cut surfaces.
For effective foliar spraying, the herbicides should be mixed with some additives. These include multi-purpose adjuvants and approved surfactants. The herbicide works well when sprayed in late spring when the plant develops leaves. This continues until almost fall. This spray can be used throughout the year. However, spraying during hot summers and early spring is usually discouraged.
Biological control
Unfortunately there is no biological control method developed to manage oriental bittersweet.
Conclusion
Oriental bittersweet is an invasive weed that causes more harm than good. The plant can single-handedly destroy and kill mature trees if left on its own. Its aggressive nature makes it hard to control. Our environmental conservation efforts should focus on eliminating such plants from the ecosystem.
Its ability to alter the soil content makes the soil inhabitable for other plants. This, therefore, means that reduced plant cover will cause soil erosion among other damages to the environment.
References
- Michigan University MSU Extension: Oriental bittersweet: An aggressive, invasive plant: https://www.canr.msu.edu/news/oriental_bittersweet_an_aggressive_invasive_plant
- Invasive plants atlas of the United States: oriental bittersweet https://www.invasiveplantatlas.org/subject.html?sub=3012
- Extension: Invasive in the Spotlight: Oriental Bittersweet https://extension.unh.edu/blog/invasive-spotlight-oriental-bittersweet
- State of Minnesota Department of Agriculture: Oriental Bittersweet https://www.mda.state.mn.us/plants/pestmanagement/weedcontrol/noxiouslist/orientalbittersweet
