October 25, 2007 at 8:35 a.m.
Buckthorn and its control
Buckthorn and its control
In 1999, the MN Department of Agriculture declared European or common buckthorn a restricted noxious weed. This means that sale, transportation, or movement of this plant is prohibited statewide by the Department of Agriculture. By 2001, glossy buckthorn was added to the list. Both species are considered invasive and spread rapidly and replacing native species through out the state.
Common or European buckthorn is native to Europe and was brought to Minnesota in the mid 1800's as a hedge material. Nurseries stopped selling in the 1930's but many hedges can still be found in yards across Minnesota.
Glossy buckthorn, also from Europe has been sold as nursery stock for many years.
European buckthorn is the most problematic of the buckthorn species because it is both drought and shade tolerant. This enables it to become invasive in woodland under-stories or at the edges of prairies or fields. In recent years, glossy buckthorn has also become invasive mainly in wetlands and moist woodlands.
Both types of buckthorn have berry clusters that attract birds and mice. The berries have a severe laxative effect that causes the seed to be spread to many areas.
Common buckthorn can grow to a height of 20 feet while glossy buckthorn rarely gets over 12 feet high. The two strong characteristics of buckthorn are the prolific berry clusters and leaves that stay dark green on the tree well into winter. This is well after natives have turned color and shed their leaves.
There is much confusion with buckthorn and similar species. This is especially true for buckthorn and chokecherries. In fact, both at the Almelund Threshing Show and at plant clinics, gardeners brought in samples and had us identify the difference. The leaves of buckthorn have curved parallel veins, while the leaves of chokecherries have veins that are not parallel. The berries of buckthorn are black with severed seeds, while the berries of chokecherries are red or black with a single hard seed. The juice of buckthorn berries will show a greenish tinge when they are crushed on white paper.
Both mechanical and chemical treatment may be used to remove buckthorn. It does not re-sprout from underground roots, but it can re-sprout from the buds at the base of stems if they are not cut close enough to the ground.
If the buckthorn stand contains individual plants 3/8 inch in diameter or less, hand pulling may be the most effective method of removal. Plants greater than 3/8 inch in diameter may be more difficult to pull out of the ground, so they may need to be dug up.
When controlling large quantities of buckthorn, cutting the stems, then painting or spraying the stumps with the herbicide glyphosate (sold as Roundup) is most effective. Buy the concentrated form containing 25 percent or higher amounts of active glyphosate.
The proper time to cut buckthorn and apply Roundup is when the plant is active or when the leaves are fully expanded and the temperatures are above 32 degrees. This is to ensure the herbicide is taken up by the plant. It must be applied within 24 hours of cutting but for best results apply immediately after cutting. Always read the label and follow directions when applying any chemical.
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VOICE MAIL: You can leave a question for a volunteer Master Gardener at 651-674-4417. Depending on the volume of calls, they try to respond within a couple of days. During office hours ask for the Master Gardener voicemail, after hours, select ext. 18. You can also get your question answered on the web at: www.extension.umn. edu/askmg.
The Chisago County Extension Office will be moving sometime in early December. Stay tuned to this column, or check our website for more information as plans are firmed up.
www.extension.umn.edu/county/chisago/mg/
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