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Master Gardeners of Goodhue County

Master Gardeners of Goodhue County

Battling Buckthorn on Your Property

David Velasquez, Goodhue County Master Gardener Intern

Buckthorn is designated as a restricted, noxious weed in Minnesota. So why is it so pervasive on my property and the property of so many landowners? Originally buckthorn was imported as an ornamental. Most Minnesota nurseries have voluntarily stopped selling this tree because of its ability to escape cultivation, which is the issue. When uncontrolled, buckthorn can form dense thickets in forests, yards, parks, and roadsides. It will crowd out native plants and displace the native shrubs and small trees in the mid-layer of the forest where many species of birds normally nest. It is important for property owners to recognize and remove buckthorn in order to protect their local environment.

Description

How do you recognize buckthorn? There are two varieties - common or European and glossy or alder buckthorn. I have a lot of common buckthorn on my property and its characteristics are: shrub habit, with several stems possibly originating from one spot, but it can reach 20-25 feet in height. If not controlled it can form dense thickets, which is why it was popular as a hedge plant when first introduced. The leaves are dark green, dull to glossy, and oval-shaped with finely toothed edges and 3-5 pair curved leaf veins. Leaves stay dark green and on the tree late into autumn. Buds are opposite and there is a sharp thorn at tip of the twig, hence the name. The round, berry-like fruit is one-quarter inch in diameter, arranged in large clusters and is green/black in color.
Each fruit has 3-4 seeds and the berries are persistent. I initially attack the female trees with berries to reduce the opportunity for spreading as efficiently as possible. Birds do not seem to be particularly fond of the fruits, but will eat the berries in late fall and winter when food sources are scarce. The fruit contains a laxative so the seeds pass through quickly and therefore not only have little nutritive value, but also are efficiently dispersed. Buckthorn seeds can remain viable for up to 5 years.

Removal

Once you have identified buckthorn, there are several ways to remove it. Burning is one method, but not usually practical. For seedlings less than about three feet tall, hand pulling is an option, if tedious. A mattock might be a good tool to consider. For larger trees, up to about two inches in diameter, a Weed Wrench works well. I have a medium sized one. It works like a lever - the trunk can be gripped between two jaws and pulling on a long lever of the tool tightens the grip and provides a mechanical advantage to pull the tree out by the roots (see References to borrow one). For mature trees, cutting is the best approach, but the stump must be treated with an herbicide or it will resprout vigorously. Stumps should be treated immediately after cutting (within 2 hours) with an herbicide containing Triclopyr (such as Ortho Brush-B-Gon or Garlon 3A or 4) or Glyphosate (Roundup) to prevent re-sprouting. Any herbicide application must be performed in strict compliance with the manufacturer's directions on the label. The best time to cut and chemically treat the stumps is in late summer and throughout the fall, when the sap is not actively flowing, but treatment can be done any time of the year.

Basal bark treatment is a method that applies chemical on the bark of a standing tree/shrub. The chemical and its binding agent are absorbed through the bark into the plant, where it kills the living cambium. For stems less than 5 cm diameter, chemical is applied to one side; for larger stems, the chemical is applied all the way around in a 30 cm (1 ft) high strip. Basal bark application can be carried out in all seasons. A paint brush or ultra-low volume sprayer can be used to apply the chemical to the bark.
Buckthorn treated in this fashion can be left standing or cut at a later date. Higher concentrations of chemical may be needed for large (tree sized) buckthorns.

Frilling involves killing a standing tree by applying herbicide to a gash cut in the bark. The tree is gashed with an axe or chain saw and the herbicide is applied directly in the gash, killing the tree immediately. While this method requires a little more time than basal bark treatment, it is generally more effective as the chemical is applied directly to the growing parts of the standing trunk. This technique may be the most effective method to kill large buckthorn trees.

Ongoing Treatment
Once begun, control methods may be needed for many years. Buckthorn seeds in the soil can remain viable for three to five years. It is important to control seedlings that emerge after initial control efforts. With no follow up control, buckthorn will come back.

Replacement

Replanting of desirable tree, shrub and herbaceous species after buckthorns have been removed would be a good idea. The goals of plantings may include privacy, protection, landscape accents or borders. Some suggested plantings would include lilac bushes, highbush cranberry, nannyberry, American hazelnut, juneberry or pagoda dogwood for privacy, barberry, shrub roses, juniper, or arborvitae for hedging or protection, butterfly bushes, trumpet vines and honeysuckle to attract hummingbirds and butterflies during the spring and summer months. Winterberries develop bright red fruits in late fall that are eaten by a variety of birds throughout the winter (MNLA 1998). Pin and chokecherries are good native substitutes whose fruits can also be eaten by humans. A reputable landscape or garden center can also provide specific recommendations.

References
http://www.extension.umn.edu/gardeninfo/weedid/woody/commonbuckthorn.html
http://www.dnr.state.mn.us/invasives/terrestrialplants/woody/buckthorn/control.html
http://www.thamesriver.on.ca/Invasive_species/Images/Buckthorn_factsheet_lowres.pdf
http://www1.extension.umn.edu/gardeninfo/components/info_landscaping.html
http://blog.lib.umn.edu/mgweb/goodhue/popular_topics/be_a_buckthorn_buster_video.html#more

The Goodhue County Master Gardeners have purchased a Weed Wrench that you can borrow free with a minimal security deposit that will be refunded when the Weed Wrench is returned. You can sign up to borrow the Weed Wrench or get a free fact sheet on buckthorn at the U of MN Extension office located at the Government Center, Room 201, 509 West 5th St, Red Wing, MN. Please call Robin at 651-385-3100 for more information on availability.