Moose Lake Star Gazette - Serving Carlton and Pine Counties Since 1895

By Kim Metz
Moose Lake Star-Gazette 

Controlling an invasive species: Buckthorn

 

October 3, 2019

Minn. Dept of Ag.

Buckthorn is a non-native, invasive shrub or small tree that is rapidly taking over our natural areas and crowding out native species. There are two kinds in Minnesota: Common Buckthorn (Rhamnus cathartica), which thrives in the woodland understory, and Glossy Buckthorn (Rhamnus frangula), which prefers wetlands.

Buckthorn was introduced into the U.S. from Europe in the mid-1800's. It has spread out of control and threatens the future of forests, wetlands, prairies and other natural habitats.

Buckthorn is very adaptable, tolerating sunny, shady, wet and dry conditions. It out-competes native plants for nutrients, light, and moisture. It degrades wildlife habitat by forming an impenetrable thicket of vegetation. The female plants produce thousands of blue berries. They have multiple seeds and have a laxative effect on birds which contributes to its spread.

Both types of buckthorn are now classified as Restricted Noxious Weeds in Minnesota. This means that importation, sale, or transportation is prohibited statewide by the Department of Agriculture.

Autumn is a great time of year to identify and eliminate buckthorn, as it holds its leaves longer than most other trees and shrubs. If you see a small tree/shrub/ understory layer that is mostly green in late October into early November, it is most likely buckthorn. The leaves of Common Buckthorn are oval, dark green, dull to glossy with finely toothed edges and 3-5 pairs of curved leaf veins, and an alternating leaf stem with a thorn on the tip of the branch. Trees are 10 – 25' tall, frequently multi-stemmed. Glossy Buckthorn is less common; the leaves are oval, smooth, dark green, glossy, with toothless edges and 8-9 pairs of leaf veins. Trees are 10 -18' tall, upright and oval form.

A heavily infested area can seem hopeless, so it's best to assess your site, make a plan and prioritize your efforts. Eliminating female trees covered with berries will stop the reproduction cycle. If you have areas with relatively few buckthorn trees, start your management there and keep those areas nice. Then work towards the areas that are more heavily infested. Continue to follow-up in the areas where you have previously removed buckthorn.

Remove small buckthorn plants by pulling or digging them. They do not have strong roots and autumn rains often soften the ground and make this task easier. For larger buckthorn, use a pruning saw to cut trunks off at the base. Roots will not re-sprout, but a stump will re-sprout vigorously. To prevent re-sprouting, apply a concentrated herbicide such as 25% glyphosate (sold as Round-up – check that it's 25%) or triclopyr (Brush-B-Gon) to the cut surface of the stump within 2 hours of cutting. Be sure to follow all label directions when applying herbicides. If you don't want to use herbicides, you can dig the stump out or cover it with a tin can or black plastic, and leave it in place 1-2 years.

Education is key to controlling and eliminating buckthorn. Many people are not aware that buckthorn is a problem, so tell your friends and neighbors.

The DNR has put together a very informative brochure on Buckthorn. The Extension office in the Pine County Courthouse has some brochures available; stop by to pick one up.

 

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