European Buckthorn is My Favorite Plant. Not!
(this article was published in Sagatagan Seasons 6: 3 (Nov 2003)
My students often joke that I describe every plant we study as my �favorite� plant. Though I am admittedly guilty of loving lots of different plants, I have never had many kind words for European buckthorn (Rhamnus carthartica). This European shrub was naively introduced to Minnesota as a hedge plant and it served this purpose well. In fact, it was too successful. Since its introduction in the mid-1800�s, European buckthorn has escaped cultivation and has spread extensively into the understory of so many woodlands that they are now officially considered �Restricted Noxious Weeds� and it is prohibited to import, sell, transport, or propagate them in the state.
Once European buckthorn becomes established it forms dense thorny thickets that shade out native plants and reduce species diversity. Bird populations also decline because native foods are reduced and the plants don�t provide suitable nesting sites. European buckthorn is able to out-compete our native vegetation because it leafs out early in the spring and stays green later in the autumn than our native species. Buckthorn also releases chemicals that inhibit the growth of neighboring plants (a phenomenon called allelopathy). To make matters worse, the berries and bark are toxic. They contain chemicals that cause diarrhea and vomiting if ingested. Not too long ago I heard a story about a family who had a rather nasty experience after eating some jelly made from the berries. Birds avoid eating buckthorn berries if other foods are available because they, like us, suffer ill effects (i.e., diarrhea). However, when they do eat the berries the undigested pigments in their droppings leave a messy stain on our homes and sidewalks.
Fortunately, European buckthorn is not currently a problem in the St. John�s Arboretum. The few plants that have initiated an assault on our woodlands have been exterminated by the watchful arboretum staff. St. Benedict�s is not quite so lucky. The campus woods are infested with European buckthorn. We plan to have a buckthorn slaughter day at St. Ben�s later this year. If you�d like to join us call me (363 � 2782) for more details.
Fall, especially late September and early October, is the best time of the year to control European buckthorn because it is easily identified � buckthorn is the only shrub in the woods at this time that will still have green leaves. Small plants can be pulled out of the ground by hand or a root puller. Larger plants should be cut and the stump painted with a potent herbicide like TordonTm or RoundUpTm. This procedure is most effective in the fall when the plant is moving nutrients from the stems into the roots. If you have minimal time, focus on removing the female plant that produce berries � at least you will limit the potential spread of the plant.
If you want to learn more about buckthorn and its management, consider attending the Woodland Owner�s and Uses Conference that will be sponsored by the St. John�s Arboretum on Saturday October 11, 2003 (for more information see the information elsewhere in this issue). Janet Larson, a buckthorn expert will present a session on invasive plants. In addition, check out the excellent article �Why should we battle buckthorn� by Dianne Plunkett Latham in the Summer 2003 issue of the Minnesota Native Plant Society newsletter, The Plant Press.