Controlling Buckthorn on Your Property

In many Ontario locations, buckthorn seems to have reached a type of threshold, with the population now increasing at an exponential rate. This highly invasive shrub is noted for prolific seed production, high rate of germination and rapid growth.  Seedlings establish best in high light but also germinate and grow well in shade, with an ability to thrive on a variety of sites. 

Taken together, these facts make this a particularly devastating shrub as it establishes within open areas, hardwood woodlands, softwood plantations and even wetlands.  Control becomes especially difficult in wooded areas. Native woodland plants such as trilliums are threatened, with natural regeneration of preferred tree and shrub species tending to be dominated by buckthorn.  Although some landowners value buckthorn species as wildlife shrubs, this is a mistake.  Buckthorn species are ultimately destructive to the natural biodiversity required to sustain our native ecosystems, including wildlife.

Description

Common buckthorn (Rhamnus cathartica) and glossy buckthorn (Rhamnus frangula) are native to Europe.  Buckthorn was imported to North America in the late 1700s, cultivated for hedges and wildlife habitat purposes. It is now naturalized from Nova Scotia to Saskatchewan and into the northern U.S. states.  As buckthorn is the alternate host of oat rust, it was classified as a noxious weed and controlled through eradication efforts, extensive livestock grazing and intensive agricultural practices.  As oat varieties with rust resistance were developed and land of lesser productivity abandoned for agricultural uses, buckthorn has flourished.




The tip of the twig on
common buckthorn is
often thorn-like and very
sharp on dead twigs. 1
Buckthorn can grow 20 feet in height, with wide-spreading crowns, often with more than one stem.  The young, brown-gray bark is smooth and shiny, with prominent small white dots (lenticels or pores), and can be confused with other species, e.g., cherries.  Mature bark becomes scaly with horizontal lenticels.

Buckthorn leafs out early and retains leaves late in the growing season; the green leaves make it very recognizable in late October and early November. The clusters of plump black fruit (>1 cm in diameter) persist on the tree until late winter. Birds consume the fruit, usually when other food becomes scarce, with the seeds passing through their digestive system and then defecated.





Buckthorn fruit clusters
(glossy buckthorn above)
will persist on the tree until
late winter. 2

The common buckthorn leaf is oppositely arranged on the twig, dark shiny green in colour, egg-shaped with small rounded teeth on the leaf’s margin.  The tips of the twigs are often thornlike and are very sharp on dead twigs. The leaves also have a distinctive vein that curves towards the tip of the leaf.

The glossy buckthorn leaf is alternately arranged on the twig, oval in shape, and the margin of the leaf is smooth. There are no thorns on the tip of the twig and the buds lack bud scales.

Habitat

Common buckthorn is both drought and shade resistant and grows on well-drained sands, clays and poorly drained soils.  It will be found growing on a wide array of sites, ranging from fencerows, rocky sites, open forested areas, abandoned fields and roadside ditches.  Glossy buckthorn is less shade tolerant and grows well on wetter sites.

Ecological Impact

Buckthorn can spread very quickly and form dense thickets, reducing the growth and survival of native species. For example, common buckthorn can form a near monoculture in the understory of the forest, completely suppressing the regeneration of seedlings, spring ephemerals and other ground flora. 

An interesting buckthorn fact has to do with its alleliotrophic characteristics (i.e., other plants are repelled from growing nearby).

Control Options

There are several mechanical and chemical control measures.  Learn to identify the plant and remove isolated plants before they produce seed. Eradicate the most prolific seed producers (e.g., along fencelines) first; a follow-up treatment is usually required for the abundant seedlings appearing in the next three years.  Then concentrate on high-priority areas such as the most productive area of your woodlot or your favourite natural area. Pull smaller plants as you take regular walks through your property or take a small hand spray bottle of herbicide for precise chemical application to individual plants. 

Mechanical control – options for buckthorn include cutting, pulling, girdling, grazing, mowing, burning and flooding. Be prepared for sucker growth and germinating seedlings after removing mature buckthorn.

  • Cutting – cutting or girdling stems is effective only if followed by an immediate application of herbicide (see below) to fresh stumps or girdled bands to prevent sprouting.

  • Pulling – small plants up to 1 cm in diameter or 1 metre in height can usually be pulled when the soil is moist. Larger plants can be dug or pulled using a weed wrench or tractor.

  • Grazing – livestock usually find buckthorn seedlings succulent and can control new regeneration (i.e., sprouting after removal of older and larger stems) along fencelines and in older fields.

  • Mowing – mowing can be effective, but is required for two to three consecutive years, reducing vigour, and leading to eventual mortality.

  • Flooding – in wetlands where the water table has been artificially lowered, glossy buckthorn may be controlled by restoring the water to its natural level.

Herbicide options – the use of herbicide is the most effective option for control.  Herbicides with the active ingredient triclopyr or glyphosate are effective against buckthorn.

  • Foliar application – herbicide applied using a backpack sprayer done from early spring to mid-summer (during the peak growing season) has proven to be effective.  If there is a concern about damaging adjacent growth, the plant’s green leaves can be recognized in the fall at a time when it is still actively growing; most other plants have shed their leaves and are dormant.

  • Basal bark treatment – applying herbicide to the base of the tree should work at any time of the year. However, for optimum results it is preferable to apply it during the active growing season. 

  • Stump treatment – cutting the stems off near ground level and immediately treating the stumps with herbicide is effective and curbs sprouting.  If applied during the growing season, a small hand pump bottle allows precise stump or foliar application and minimizes contact with other vegetation.

  • Girdling or frilling – for larger stems, cutting a groove through the cambium and phloem layers of the bark to interrupt the flow of sap between the roots and the crown of the tree, combined with an immediate application herbicide, will provide good control.  Note: the cut must completely surround the bole of the stem to be effective.           

Note – all herbicide applications should be applied in accordance with the manufacturer’s label and by a knowledgeable applicator that is licensed.

Acknowledgement

This article was prepared by the Victoria Land and Water Stewardship Council in 2005 and was recently revised and updated by the OWA for this edition of the S&W Report, with information from The Landowner’s Guide to Controlling Invasive Woodland Plants.  An electronic copy of the guide is available on the OWA website at <http://www.ont-woodlot-assoc.org/sw_controlling_invasive_woodland_plants.html>.

Photo Credits

1 Chris Evans, River to River CWMA, Bugwood.org
2 Gil Wojciech, Polish Forest Research Institute, Bugwood.org

This article appeared in a past edition of the S&W Report the newsletter of the Ontario Woodlot Association.

© 2012 Ontario Woodlot Association

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