Oriental Bittersweet (EwA Guide to Common Invasive Species in Middlesex County (MA, US) )

Oriental Bittersweet

Celastrus orbiculatus

Summary ⁷

Celastrus orbiculatus is a woody vine of the Celastraceae family. It is commonly called Oriental bittersweet. Other common names include Chinese bittersweet, Asian bittersweet, Round-leaved bittersweet, and Asiatic bittersweet. Celastrus orbiculatus was introduced into North America in 1879, and is considered to be an invasive species in eastern North America. It closely resembles the native North American species, Celastrus scandens,

Short Description ⁸

Deciduous, woody, twining vine. It may reach 30 m (98.5 ft) in length. Leaves are alternate 5-12.7 cm long (2-5 in),
with pointed tips, a smooth, bright surface, and fine margin teeth. They turn yellow in the fall. Flowers are small, have five greenish-yellow petals, and are clustered in the axils of the leaves. Fruits are composed of a pulpy red aril covered by an orange-yellow outer skin; they are showy and shiny.

Source: EwA Invasive Pocket Fieldguide | © Earthwise Aware

Description ⁹

Deciduous twining shrubs; branchlets glabrous, gray- brown or brown, with sparse and inconspicuous lenticels; axillary buds small, ovate to elliptic, 1-3 mm. Petiole slender, 1-2 cm; leaf blade generally broadly ovate, suborbicular, or rectangular-elliptic, 5-13 × 3-9 cm, glabrous or abaxially sparsely pubescent on veins, base broadly cuneate to obtuse-orbicular, margin serrate, apex broadly rounded, muriculate, or shortly acuminate; secondary veins 3-5 pairs. Cymes axillary, sometimes terminal, 1-3 cm, 1-7-flowered; pedicels jointed below middle or nearly to base. Male flowers: sepals obtuse-triangular; petals obovate-elliptic to rectangular, 3-4 × 2-2.5 mm; disk shallowly cupuliform, lobe shallow, apex rounded-obtuse; stamens 2-3 mm. Female flowers: corolla relatively shorter than that of male flower; disk slightly thick, carnose; staminodes very short; ovary approximately globose; styles ca. 1.5 mm; stigma deeply 3-lobed, lobe apex shallowly 2-lobed. Capsule approximately globose, 8-13 mm wide, yellow, 3-valved. Seeds elliptic, slightly flat, 4-5 × 2.5-3 mm, reddish brown; aril orange-red. Fl. May-Jun, fr. Jul-Oct.

Competitive interactions ¹⁰

One of Oriental bittersweet's invasive characteristics is its effective utilization of energy to increase plant height, thus giving it a competitive advantage over similar plants. A study conducted in 2006 showed that, in comparison to its congener American bittersweet, Oriental bittersweet had increased height, increased aboveground biomass, and increased total leaf mass. This is not to say that Oriental bittersweet outperformed American bittersweet in all criteria: in comparison to Oriental bittersweet, "American bittersweet had increased stem diameter, single leaf area, and leaf mass to stem mass ratio", suggestive that American bittersweet focused growth on ulterior portions of the plant rather than plant characteristics emphasized by Oriental bittersweet such as stem length. This is significant as height plays a major role in allowing Oriental bittersweet to outcompete surrounding vegetation. Focusing growth on stem length allows it to be in a strong position to absorb light, while also negatively impacting surrounding plant life by creating shade-like conditions.

The species' vine-like morphology has also been shown to have negative effects on surrounding plant life. For example, evidence suggests that this morphological characteristic facilitates its ability to girdle nearby trees, creating an overall negative effect on the trees such as making them more susceptible to ice damage or damaging branches due to the weight of the plant. Additionally, studies have suggested that Oriental bittersweet is capable of siphoning away nutrients from surrounding plants. The study found this to occur in a variety of environments, suggestive of both the plant's increased relative plasticity as well as increased nutrient uptake.

One study observed that the presence of Oriental bittersweet increases the alkalinity of the surrounding soil, a characteristic of many successful invasive plant species. This alters the availability of essential nutrients and hinders the nutrient uptake ability of native plants. Though the relationship between Oriental bittersweet and the alkalinity of the soil is consistent, there are a number of proposed mechanisms for this observation. The plant's significant above-ground biomass demands the preferential uptake of nitrate over ammonia, leading to soil nitrification. It also has a high cation-exchange capacity, which also supports the larger biomass. Either of these functions could explain the increased alkalinity, but further experimentation is needed to pinpoint the exact mechanism.

⭕ Control Methods (EwA Content) ¹¹

Mechanical and chemical methods are strong allies to control and eliminate the spread of Oriental bittersweet. For effective control, two main actions are necessary: reduce the impact that Oriental bittersweet has on shrubs and trees used as support and prevent seed production and dispersal (a).

Cutting and Mowing

Hand-pulling can be helpful when the soil is moist and the population is low. With small infestations, larger plants can also be removed by digging, but it is important to be diligent and remove all the roots (a). The mitigator needs to be aware of whether the new seedlings are young individuals or clones produced by the root system of a larger individual (a).

Cutting and mowing a few times during the season are only effective if paired with chemical control to prevent regrowth. In cases where cutting and moving is the sole action to remediate the area, the plant usually regrows more vigorously, worsening the situation. For a positive impact, it is necessary to carry out annual pruning for several weeks during several growing seasons until the plant energy reserves are exhausted. (a, b).

Chemical Treatment^⚠

It is recommended to use chemical control to eradicate large plants with extensive roots that can't be fully dug out (a). When selecting a suitable herbicide for Oriental bittersweet management in a specific area, factors like herbicide effectiveness, proximity to water bodies and wetlands, presence of native species, and soil erosion risk must be weighed (a).

Foliar treatment → Well-developed Oriental bittersweet vines often wrap the branches and trunk of their host entirely, reaching the upper canopy of the host tree and preventing the use of foliar herbicides (a, b). In this case, one can free the native vegetation by cutting the invasive vine at ground level, forcing the roots and stumps to produce new shoots, and then treating the new growth by applying herbicides to the leaves.Cutting can occur any time of the year, but the herbicide should be applied after eight weeks of regrowth. If the leaves are too small when treated, the herbicide will not reach the roots (b). The dead vines will dry out and decompose over time, so pulling the vine from the trees is unnecessary, preventing further damage to the host plants (b).

Glyphosate herbicide is effective for foliar and cut-stump treatments, with peak efficacy on cut surfaces during full-leaf and active growth stages (a). It is best applied from July onward since plants are in full-leaf and growing actively. Spring treatments are ineffective due to emerging leaves and upward sap flow (b). Treating in the fall is advantageous, as Oriental bittersweet leaves persist longer than native species, reducing its impact on native species (a). Triclopyr is an alternative for Oriental Bittersweet control, applied foliarly when fully leafed in spring until the leaves start changing color in fall (a).

It is recommended to monitor an area of at least 1 km (0.67 miles) around the management area due to the dispersal of the species occurring over long distances (a).

Other chemical treatments → Stem treatment is inadvisable as it may affect desirable species, especially in a well-developed infestation. But in specific cases, its use can be considered (b). For stems over 2.5 cm (1 in) in diameter that are not closely coiled around desirable native plants, the hack-and-squirt method can be employed by making downward-angled cuts spaced no more than 2.5 cm (1 in) apart at a suitable height using a hatchet (do not girdle the stem). Apply a water-based herbicide solution using a handheld sprayer to saturate the cuts, avoiding runoff. This precise approach minimizes herbicide use (b).

The basal bark treatment is most effective on young stems with thin bark, and can be applied to stems under 2.5 cm (1 in) in diameter (a). The product used in this treatment is an oil-soluble triclopyr ester (a, b). Concentrated herbicide must be applied to a bark band around stems extending 46 cm (18 in) from the ground (a). Avoid spraying the solution on the bark of desirable trees and shrubs. Applying large amounts of concentrated triclopyr ester to vines near the base of desirable trees is extremely risky and must be avoided (b). This treatment is ineffective during heavy sap flow in spring and should not be used when snow or water prevents herbicide from being applied at the ground level or when stems are saturated (a).

Disposal

If there are no fruits, you can leave the cut vines in place to naturally decay. The removed stems and roots can also stay put, provided the roots are positioned to dry out without the risk of re-rooting, such as draping them over a branch. It's best to burn or dispose of the fruits in a landfill after bagging (c).

⚠ Disclaimers

Disclaimer #1: Harmless chemicals do not exist. Any chemical use is likely to harm non-target species and affect the soil. However, in some circumstances, chemicals might be the only way to succeed in removing an invasive species permanently. In all cases, researching and understanding the latest scientific literature before using a specific chemical or a mix of several is critical to reducing negative impact.

Disclaimer #2: Independently, several European countries recently announced future bans or massive restrictions on the use of glyphosate (e.g., Austria, Germany, France). The EU, at large, is expected to decide on the renewal of the approval of glyphosate Ultimo 2023 (More here).

Sources

[a] Oriental bittersweet, Michigan Department of Natural Resources Michigan Natural Features Inventory 2/2012. Available in: https://mnfi.anr.msu.edu/invasive-species/OrientalBittersweetBCP.pdf
[b] Oriental Bittersweet. 2020; Available in: https://extension.psu.edu/oriental-bittersweet
[c] Oriental bittersweet, Michigan Department of Natural Resources Michigan Natural Features Inventory 2/2012. Available in: https://mnfi.anr.msu.edu/invasive-species/OrientalBittersweetBCP.pdf

Sources and Credits

(c) Christine Tuccelli, some rights reserved (CC BY-NC), uploaded by Christine Tuccelli, https://www.inaturalist.org/observations/123538665
(c) Bill MacIndewar, some rights reserved (CC BY-NC), uploaded by Bill MacIndewar, https://www.inaturalist.org/observations/143895266
(c) Claire O'Neill, some rights reserved (CC BY-NC-ND), uploaded by Claire O'Neill, https://www.inaturalist.org/observations/162727247
(c) Claire O'Neill, some rights reserved (CC BY-NC), uploaded by Claire O'Neill, https://www.inaturalist.org/observations/148995025
(c) Claire O'Neill, some rights reserved (CC BY-NC), uploaded by Claire O'Neill, https://www.inaturalist.org/observations/121437124
(c) Claire O'Neill, some rights reserved (CC BY-NC), uploaded by Claire O'Neill, https://www.inaturalist.org/observations/114435987
Adapted by Esther Meirelles from a work by (c) Wikipedia, some rights reserved (CC BY-SA), http://en.wikipedia.org/wiki/Celastrus_orbiculatus
(c) Claire O'Neill, some rights reserved (CC BY-SA)
Adapted by Claire O'Neill from a work by (c) Missouri Botanical Garden, 4344 Shaw Boulevard, St. Louis, MO, 63110 USA, some rights reserved (CC BY-NC-SA), http://eol.org/data_objects/4971205
(c) Wikipedia, some rights reserved (CC BY-SA), https://en.wikipedia.org/wiki/Celastrus_orbiculatus
Adapted by Esther Meirelles from a work by (c) Claire O'Neill, some rights reserved (CC BY-SA)

More Info

iNat Map

‹ › ×