By Dan Marzu
UW-Extension Agriculture Educator Lincoln & Langlade Counties
Every year I receive a couple questions regarding controlling buckthorn. There are two types that are in Wisconsin, common and glossy buckthorn. During the 1800s, it was introduced to North America from Europe or northwestern Asia to be used as a hedgerow or a shelter-belt around fields. It spreads through seed primarily form birds eating the fruit during winter months. The fruit causes a laxative effect, causing the animals to effectively spread the seeds in their feces. Due to this ability for buckthorn to spread easily, the Wisconsin DNR has classified both common and glossy buckthorn as restricted, meaning that they are already established and are causing or have the potential to cause environmental or economic harm or harm to human health. The exception to this classification are the ‘Asplenifolia’ and ‘Fineline’ (Ron Williams) cultivars.
Both common and glossy buckthorn can grow to around 10 to 25 feet tall and creates a dense canopy that outcompetes other forest plants for sunlight. The leaves are elliptical in shape and stay green late into the fall.
Common buckthorn is found on well-drained soils located in riparian woods, old fields, and roadsides. It is also allelopathic, producing a chemical compounds that prevent other plants from growing. The leaves of common buckthorn are one to two and half inches long with tiny teeth. The twigs of common buckthorn end in thorns. This plant produces male and female plants. The female plants will have a greenish yellow, four petaled flower that produces a black fruit.
Glossy buckthorn establishes in bogs, marshes, river banks, wetlands, and pond margins. The leaves are two to three inches long, with a glossy upper surface. The underside of the leaf is dull and can have hairs. This type of buckthorn does not have any thorns. All of these plants produce a pale yellow five petaled flower that produces a red fruit that turns black when ripe.
There are methods to control buckthorn through non-herbicide methods and the use of herbicides. One of the best methods of control is to dig up or pull the plants when the plant stem is less a one and half inches in diameter. The smaller the diameter, the easier the plant can be pull. Make sure you remove the root crown when using this method to prevent the plant from resprouting. Another method, though not as effective in killing the plant, is mowing. Mowing once in summer before the seed is produced and again in fall after the plants have resprouted will begin to decrease the vigor of the plants. It will take several years of mowing to kill the plant. If seeds are present be sure to clean the mower before moving it off the property to ensure seeds don’t get spread accidentally. Mowing is best used when using another control method such as chemical. You can also try to establish shade tolerant woody species such as sugar maple to out compete the buckthorn plants. These plants if established will decrease the light level and reduce the productivity of the buckthorn and possibility prevent seeds from germinating. Again this will take several years as the trees grow to outcompete the buckthorn.
There are a variety of methods to control buckthorn with herbicides. The first method is to spray a herbicide pre-emergence. This means to apply a herbicide before the buckthorn germinates. These type of herbicides will not damage established plants, but will prevent seeds from germinating. This method may also prevent desirable plants from germinating. The second application method is called foliar. For this type of method you apply the herbicide directly to the plants. If the herbicide is applied to desirable plants, it may cause damage to those plants. Another method, called cut stump, is applying the herbicide directly to the surface of the stump. You will need to apply the herbicide no longer than one hour after cutting to ensure the herbicide is absorbed into the stump. Another method that involves cutting the trunk of the plant is called hack-and-squirt. This method, cut the trunk every three to four inches six to eighteen inches above the ground. Once the trunk is cut apply the herbicide directly into the cut surface. Do not use this method if there is heavy sap flow as the herbicide will not be absorbed into the plant. The final method using herbicides is called basal bark. With this method a herbicide is applied in a ring six to eighteen inches wide at the base of the plant. This is best if the plants have a diameter of less than six inches in diameter. If you are using herbicides always read and follow labeled directions.