There are over 100 species of buckthorn (Rhamnus) worldwide, most of which are native in northern temperate regions. We are primarily interested in two species which have been identified as problematic invasive species.
- Glossy Buckthorn, R. frangula, is from Europe. It grows to about 20 feet, has alternate buds, red fruit that turns dark at maturity and is irregular in shape. It aggressively invades wetlands and moist woodlands. Columnar forms in the nursery trade are narrow and upright, growing to 12 feet high.
- Common or European buckthorn, R. cathartica, is extremely aggressive on lowland and upland sites. It grows to 20 feet with a spreading irregular crown. The bark is rough gray/brown. The fruit is glossy black and the leaves are finely toothed, pointed and a glossy, dark green. Diagnostic characteristics include prolific berry clusters and leaves that stay dark green well into winter. Common buckthorn is widely distributed in Minnesota and is very common in the understory of urban and rural woodlots.
Buckthorn control is labor intensive. Strategies include one or more of the following:
- Physical removal where plants are sparse is the most expedient and environmentally friendly method. Dig, pull or chop the plants out of the ground. Buckthorn pulls out most easily up to 3/8 inch caliper or diameter. Larger buckthorn can be removed with the aid of mechanical equipment like the Root Talon® or Weed Wrench®. Buckthorn doesn't re-sprout from underground roots.
- Crown removal without chemical treatment eliminates fruit, however, stumps re-sprout. Re-sprouting stumps can be treated with contact herbicides or with fire for several growing seasons.
- Fire is most effective against seedlings and small saplings. Be aware of local and state fire codes and local permits and ordinances.
- Cut stumps can be chemically treated. Cut the buckthorn trunk as low to the ground as possible before treating. Products containing glyphosate (Round-Up) or triclopyr (Garlon) offer good control and can be purchased without a special license. Garlon is preferred over Tordon because of reduced potential nontarget effects (herbicide damage) to other dicots (broadleaf trees, shrubs and forbs). Both are effective on buckthorn. Both are relatively nontoxic to humans." ALWAYS READ LABELS AND FOLLOW DIRECTIONS when using chemicals.
- Basal bark treatment allows application of chemical to the lower bark of the tree without having to cut the top. Garlon 4 mixed with crop oil or diesel fuel is the preferred herbicide for basal bark treatment.
Sources: MN Dept. of Ag. Bulletin Buckthorn and Its Control; Hennepin Parks, U of MN Dept. of Forest Resources; Buckhorn Links