Winter can be a good time to scout for buckthorn and remove it before spring. Common buckthorn and glossy buckthorn are both easy to spot in early winter because they tend to retain their green leaves much longer than other deciduous shrubs.

The buckthorn plant is an example of a good idea gone badly. Both species were brought from Europe for use as hedge and privacy plantings. Unfortunately, they have become very serious invasive plants known for dense thickets in woodlands, yards, parks and roadsides. If you have ever attempted to walk through a buckthorn thicket, you know what I mean.

As with most exotic invasive plants, buckthorn can spread quickly, crowding out native plants, shrubs and small trees. Their dense canopies also impact oak regeneration in native forests by shading and outcompeting young oak seedlings.

Common buckthorn is a rather small tree that can reach a height of 20 feet with a spreading crown. The bark is brown with silver cork projections. Be sure not to confuse buckthorn with cherry or plum, as they also have reddish to black bark with light-colored lenticels.

If you cut a buckthorn branch, the sapwood will be yellow and the heartwood orange. The twigs usually contain sharp, stout thorns that can be quite painful if encountered. If leaves are present, they are broad and elliptical with a pointed tip; they are dark green in summer (lighter green or a bit yellow in fall-winter), with small “teeth” on the leaf margins. The fleshy, black fruit is preferred by birds, which help spread buckthorn. The seeds can remain viable for two to three years.

Glossy buckthorn is very similar in appearance to common buckthorn, but usually lacks the thorns on the branch tips. The leaves are similar but lack the “teeth-like” margins. The fruit is red to dark purple with a similar number of seeds.

Outcompeting

So, why is buckthorn such a serious exotic invasive plant? As mentioned earlier, buckthorn outcompetes native plants for nutrients, light and moisture, and directly competes with oak seedling regeneration. Remember, young oak seedlings need full sunlight to grow and thrive. Aggressive, shade-tolerant woody plant species will restrict or even prevent the growth of young oak trees.

Further, buckthorn degrades wildlife habitat, contributes to erosion, and can serve as a host for insect pests such as the soybean aphid, and as an alternate host for crown rust diseases. Dense thickets restrict recreational use, making it very hard to walk through wooded areas. Finally, because buckthorn is an exotic plant, it lacks any “natural controls” to help restrict its growth and spread.

Management of buckthorn can be quite challenging. Prevention and early detection are key. Because the seeds are spread by birds, things can get out of hand very quickly. Control of buckthorn involves a combination of mechanical, cultural and chemical measures.

Mechanical control involves pulling young seedlings and saplings, and grubbing out larger plants. You must remove the root crown to prevent resprouting. Prescribed fire is a common culture measure that may kill seedlings and top-kill larger plants, but it must be combined with mechanical and chemical tactics. Chemical treatments involve the use of herbicides applied to the foliage, bark or cut stumps. When using any pesticide, be sure to read and follow the label for before, during and after use.

For more information on buckthorn, talk to your local forester or Extension office.

Miller is a horticulture professor at Joliet Junior College in Joliet, Ill., and a senior research scientist in entomology at The Morton Arboretum in Lisle, Ill. Email your tree questions to him at [email protected]. The opinions of this writer are not necessarily those of Farm Progress/Informa.