Invasive Buckthorn


Common buckthorn (European buckthorn),Rhamnus cathartica,and Glossy buckthorn,Frangula alnus(previously namedRhamnus frangula), arelarge shrubs or small trees (10-25’ in height) that are non-native invasive species. Both can form dense thickets displacing native tree and shrub species. Common buckthorn prefers drier sites while glossy buckthorn favors wetter habits including river and stream banks and pond edges. Plants of both species can establish themselves in fence rows, open fields, roadsides, open woods, and woodland edges. Common buckthorn is the alternate host forcrown rust of oats(Puccinia coronataf. sp.avenae) that affects both yield and grain quality and is an overwintering host for soybean aphids.

Identification

The leaf arrangement for common buckthorn can be opposite or subopposite, meaning its leaves are slightly offset from opposite but also not far enough apart to be considered alternate.

While both species have leaves of similar size, 1-3” in length and ¾-1 ½” in width, they differ in several critical ways. Common buckthorn leaves have a very distinctive venation pattern with 3 to 5 pairs of veins that run roughly parallel and curve as they approach the leaftip. Theleaf margin hasfine,roundedteeth,andthe petiole is ¼-1” in length.

Glossy buckthorn leaves have 8-9 pairs of veins with a smooth or entire leaf margin. Theleaves are glossy darkgreen,and thepetiole is ¼-½” in length.

Common buckthorn is dioecious with male and female flowers on separate plants. Female plants are more numerous and can begin to produce flowers and fruit as early as four years of age. The flowers have four, greenish-yellow petals and are produced in clusters of 2-6. The resulting fruits are fleshy, ¼” in diameter, and are black when ripe. 

Glossy buckthorn has complete flowers with both male and female reproductive structures present within theflower. The flowers have five, greenish-white petals and can appear singly or in cluster. The fruits are ¼” in diameter and change from red to black as they ripen.

In winter, common buckthorn can be identified by its ¼” elongated, dark brown buds.The terminal bud is typically absent having been replaced by a modified spine ¼” to 7/8” in length.

 The sapwood is yellow, and the heartwood is pink to orange. 

Glossy buckthorn has a prominent brown terminal bud that is covered with hairs, and which is much larger than the lateral buds. The stems are marked with lenticels. Glossy buckthorn does not have a spine. 

Look-a-likes

Several native buckthorns and other woody shrubs can be confused with these invasive species. When in doubt, samples can be submitted to the C. Wayne Ellett Plant Pest Diagnostic Clinic for identification.

Carolina buckthorn,Frangula caroliniana, has an alternate leaf arrangement. The leaves are 2-5” in length. Theflowers are yellow-green, and the stalks arepubescent.The fruits are round, 1/3” in diameter and change from a bright red in summer to black when ripe. Its buds are very small and fuzzy. Broken branches produceastrong almond scent. This species is more commonly found in the southern U.S.

Alder-leaved buckthorn,Rhamnus alnifolia, is a small plant reaching less than 3’ at maturity. This species has an alternate leaf arrangement. Leaves have 5-9 pairs of veins and leaf margin has tiny, serrated teeth and a pair of stipules are present at the base of the petiole. The flowers do not have petals but have 5 sepals giving the flowers a star-like appearance. This plant does not have thorns.

Shrub dogwoods,Cornus spp., have opposite leaves with smooth margins. The flowers and fruit are in flat cymes rather than in the axils of the leaves. The fruits are white or blue rather than black when ripe.

Deciduous holly,Ilex spp., have alternate, elliptic to oval leaves, and the fruits are orange or red when ripe.

Chokeberry(Prunus virginiana),has alternate leaves with a finely serrated leaf margin and an acuminate leaf tip. The white flowers are produced in 3-6” racemes and the edible fruit are purple black when ripe.

Management

Management practices are the same for both invasive species. When the seedlings are young less than ½” in diameter, they can be easily removed by hand pulling because of theirfibrous,shallowroot systems. When plants are 1 ½” in diameter or less, they can be controlled by cutting or mowing, but resprouting may occur, so continued maintenance is required. Chemical control is more effective for plants with a stem diameter greater than 1 ½”. Herbicides containing the active ingredients triclopyr, and/orglyphosate can be applied to cut stumps or directly to the foliage during the growing season. The most effective time to control buckthorn is August to November. Before applying any herbicide be sure to read the entire label and follow all the instructions and restrictions. Care should be exercised to prevent the herbicide from coming into contact with desirable plants.  Since buckthorn seed can remain viable for five years, continued monitoring and control will be needed to prevent regrowth. For additional information on herbicide control measures can be found athttps://extension.psu.edu/buckthorn.

References and additional information

Minnesota Department of Natural Resources. n.d. Buckthorn What you should know. What you can do (EWR_395_17) [Fact sheet].https://files.dnr.state.mn.us/natural_resources/invasives/terrestrialplants/woodyplants/buckthorn_what_you_should_know.pdf

Minnesota Wildflowers. n.d. Rhamnus alnifolia( Alder-leaved Buckthorn).https://www.minnesotawildflowers.info/shrub/alder-leaved-buckthorn

Natural Resources Conservation Services. n.d. Pest Management Invasive Plant Control Buckthorns - Rhamnus cathartica&Frangula alnusNH-595 [Factsheet].https://www.nrcs.usda.gov/Internet/FSE_DOCUMENTS/stelprdb1081644.pdf

Renz, Mark, Brendon Panke, and Ryan deRegnier. 2012. Management of Invasive Plants in Wisconsin: Common buckthorn and glossy buckthorn (A3924-02) [Fact Sheet]. https://polk.extension.wisc.edu/files/2011/01/A3924-02-Buckthorn-control-and-ID.pdf

Seiler, John, Edward Jensen, Alex Niemiera and John Peterson. 2019. Virginia Tech Dendrology Carolina buckthorn [Fact Sheet]. https://dendro.cnre.vt.edu/dendrology/syllabus/factsheet.cfm?ID=558

Smallidge, Peter. 2018. Buckthorn – Control of an invasive shrub [Fact Sheet]. https://cpb-us-e1.wpmucdn.com/blogs.cornell.edu/dist/b/5769/files/2015/12/Buckthorn-1s2q4e9.pdf

Templeton, Skylure, Art Gover, Dave Jackson, and Sarah Wurzbacher. 2020. Invasive Plant Fact Sheet Buckthorn Common (Rhamnus cathartica) and Glossy Buckthorn (Frangula alnus[syn.Rhamnus frangula]) [Factsheet].https://extension.psu.edu/buckthorn

Wieseler, Susan. 2005. PCA Fact Sheet: Common Buckthorn [Fact Sheet]. https://www.invasive.org/alien/fact/pdf/rhca1.pdf