Winter is practically here, and most plants have lost their leaves, woody invasive species, such as Japanese barberry (Berberis thunbergii), common buckthorn (Rhamnus cathartica), and glossy buckthorn (Frangula alnus), can still be managed during the winter months. They may be easier to manage this time of the year, because neighboring plants are not in the way, allowing for easier access to the target species. Identification of these species is possible in the winter but can be tricky, so KISMA suggests focusing management efforts on previously known patches of these woody invasives.

Japanese barberry is a small understory shrub with red, egg-shaped berries that can persist into winter. Because other native plants also have small red berries, it is important to look for other characteristics as well; looking at the stem and roots can be especially helpful with identification. Japanese barberry stems will have spines along the length of the stems, though the stems can be difficult to see once the plant has dropped its leaves.

Wear sturdy gloves when pulling or digging up this species to prevent injuries from the spines! To manage Japanese barberry, hand-pull any small plants and use a shovel to dig out any root masses. Removing as much of the root as possible is important since this can be a stubborn species and will resprout if given the chance. The stem and roots are bright yellow on the inside, which also makes them distinguishable from most other plants.

Common and glossy buckthorn are two more woody invasive species that can be managed in the winter. Occasionally these species have small, round, dark purple berries that persist into the fall and winter months, especially for common buckthorn.

Common and glossy buckthorn are known to keep their leaves much longer than many native species, but they will likely have lost their leaves by early winter-see resources below for summer identification tips. In the winter months, common buckthorn can be identified by truncated thorns at the tips of many branches and along mature branches and stems, whereas glossy buckthorn will never develop thorns. Glossy buckthorn has prominent lenticels, or white “spots,” along their smoother gray stems and branches no matter their size, whereas common buckthorn stem bark becomes roughened with age and lenticels become less apparent. When the bark of common buckthorn is scraped, it reveals a yellow-orange inner bark.

Like Japanese barberry, buckthorns can be managed in the winter. Hand-pulling small plants and saplings is very effective for these species. Because the stems can snap more easily in the cold weather, loosening the soil first with a shovel before pulling will help. If a plant is too large to pull by hand, you can use a weed wrench to help pull it from the ground. Since buckthorns can grow to be fairly large, you can also cut the stem. If you cut the stem of the buckthorn, it is important to cover the stump with a garbage bag, tarp, or other opaque, dark, sturdy plastic to prevent light from reaching the stump. After you cover the stump, secure the covering to the stump using zip ties or another method, then weigh the covering down with heavy materials such as rocks or logs. Keep the covering in place for 2 growing seasons and make sure to check it for any signs of breach and regrowth throughout the growing months.

Keep an eye out for native lookalikes when managing these species. Beneficial native species such as alder and dogwood have similar characteristics and can be much harder to distinguish in the winter than the summer. For example, alder also have lenticels on the stem, making them look very similar to glossy buckthorn in the winter. In the summer, alder leaves are double serrated, which makes them easy to distinguish from the smooth-margined glossy buckthorn leaves. Dogwood can be distinguished from buckthorn in the summer by slowly pulling apart the leaves and looking for fibrous strands of the veins connecting the pieces. Glossy buckthorn will not have these strands, whereas dogwood will. Identification of these species can be much easier in the summertime, so KISMA recommends landowners identify patches of these species in the summer months and practice management through the winter on known patches so as not to remove any native species.

While winter in the Keweenaw can be harsh, these invasive species are persistent. The key to the management of invasive species is perseverance and consistency. The fall and winter months can be prime time to keep up with the management of some of these species so you can focus your summertime attention on others.

If you think you have found an invasive species and would like more information, you can go to the MISIN website, https://www.misin.msu.edu/, or contact KISMA at kisma.up@gmail.com for help with identification or guidance on management. You can also check out the website for Woody Invasives of the Great Lakes (WiGL) for more information about these woody invasive species and others, https://woodyinvasives.org/. For comparison of the buckthorns and lookalike species check out this website: https://www.1854treatyauthority.org/images/IDComparisonsofInvasiveBuckthorn&HoneysuckletoNativePlantsinNEMN.pdf. For glossy buckthorn-specific information check out this website from the Minnesota Department of Agriculture, https://www.mda.state.mn.us/plants/pestmanagement/weedcontrol/noxiouslist/glossybuckthorn.