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November 4, 2024

November Weed of the Month: Round Leaf Bittersweet Noxious Weed Status Change

In 2023, round leaf bittersweet regulation changed to Prohibited Control

Monika Chandler, Minnesota Department of Agriculture

Round leaf bittersweet (Celastrus orbiculatus) is a deciduous woody vine native to eastern Asia. It’s a standout beauty in the fall and winter with bright, red fruit surrounded by yellow capsules. It was introduced as a landscape plant in New York in 1886. The trouble began when it escaped cultivation. Birds and other wildlife eat the fruit containing seed and move the seed to new locations.

Round leaf bittersweet infestations were not documented in Minnesota prior to 2010. It was considered a USDA Plant Hardiness Zone 5 species, and none of Minnesota was Zone 5 until 2012. We thought our winter cold would kill round leaf bittersweet and spare our forests from this destructive vine. Unfortunately, that was not the case.

Without the insects and diseases that keep this vine in check in its native range, the vines have a competitive edge over Minnesota native vegetation. Round leaf bittersweet vines are very cold hardy and grow vigorously here. The vines wrap around tree trunks and overtake the canopy, depriving trees of sunlight. The weight of the vines, especially when covered with snow or ice, eventually bring down the trees. In the end, only round leaf bittersweet vines grow over a fallen forest. This happened in areas of Winona and Red Wing. These communities, often in partnership with the state, have done successful control work.

Round leaf bittersweet infestation in Winona, MN

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Fortunately, round leaf bittersweet was not widely sold and planted in Minnesota because it was considered a Zone 5 species. When we began learning about infestations in 2010, the Minnesota Department of Agriculture (MDA) acted quickly to regulate round leaf bittersweet as a Prohibited Eradicate Noxious Weed in 2011. This meant that it could no longer be sold and planted and that existing vines should be eliminated.

The nursery industry was very helpful and quickly pulled stock from sale. University of Minnesota Extension- with assistance from many state, county, and municipal partners- led outreach and trained thousands of people to identify, report, and control the vines. The Environment and Natural Resource Trust Fund supported the trainings and initial control work. Infestation reports streamed in from many areas of central and southeastern Minnesota.

Given that there are currently 1,938 infestations documented in Minnesota, eradication is no longer considered feasible. In 2023 round leaf bittersweet regulation changed to Prohibited Control, meaning that it can’t be sold or planted, and landowners should control the spread of this vine. Realistically, most landowners are not equipped with the forestry mowers and chain saws needed to control this vine. To mitigate the spread of round leaf bittersweet, more funding is needed for the equipment and people necessary to manage this vine.

MEDIA: For more information on Weed of the Month, contact Brittany Raveill, MDA Communications, at [email protected] or 651-201-6131