Growing Green: Arrest the Pest: Oriental Bittersweet
This fall I had the opportunity to visit many floral shops throughout the Metro area and outstate Minnesota, and fell in love with Bittersweet, a very popular ornamental used in fall arrangements. The good news: there is a beautiful native variety that is hardy (zone 3) in Minnesota, American Bittersweet (Celastrus scandens). The bad news: a very popular, very prolific invasive variety is also found in Minnesota, Oriental Bittersweet (Celastrus orbiculatus). Oriental bittersweet vines grow up to 66’ long and have large root systems that send up new shoots. These vines twine around trees; reducing the amount of light available for tree growth. The weight of these vines can break trees in heavy snow and strong winds, and the tough main stems will slowly strangle a tree if left to mature.
Oriental bittersweet was introduced to North America in the mid-1860s as an ornamental. It has since escaped cultivation and is severely damaging urban and natural forests and grasslands. Wildlife, especially birds, consume the fruit and move seeds to new locations. People collect the fruiting branches to make seasonal decorations resulting in additional seed dispersal.
The Minnesota Department of Agriculture has classified Oriental Bittersweet as a prohibited noxious weed on the eradicate list. This means that all of the above and below ground parts of the plant must be destroyed. Additionally, no transportation, propagation, or sale of these plants is allowed. What is an invasive species? The definition has two parts. First, they are organisms not originally from Minnesota. Second, they can harm the economy, environment, or humans.
So, how do you identify Oriental Bittersweet? Take a look at the fruit. Fruits are round and change color from green to bright red with a yellow capsule (fruit cover that splits open when mature) in the fall. Flowers and fruit are arranged in clusters along the main stem where the leaves attach to the vines. American bittersweet vines are similar, but are distinguished by their fruit and flower placement. Flowering and fruiting occur at the terminal ends of American bittersweet vines. The fruit capsule color is also noticeably different. Oriental bittersweet has yellow fruit capsules and American has bright orange capsules.
Avoid spreading Oriental bittersweet by learning to recognize it and not planting it. Do not collect and use the fruiting stems for ornamental purposes. Remove all infestations from your property. Bag or burn all fruit for disposal. Control options include manually pulling the plants prior to fruiting, or foliar herbicide application (2,4-D plus triclopyr, or triclopyr alone) in early spring or fall. Regular, weekly mowing will also control Oriental bittersweet, but less frequent mowing may result in suckering from the roots. For all management options, infested sites will need to be monitored and treated repeatedly until the seed banks are depleted.
For more information visit: www.mda.state.mn.us/plants/badplants/orientalbittersweet.aspx
To track state infestations of invasive species, visit: http://gis.mda.state.mn.us/earlydetection/?9
Robin Trott is a Horticulture Educator with University of Minnesota Extension.