Note: The author has spent 20 years bashing buckthorn at his recreational property, Oak Hills Farm, which includes about five acres of buckthorn. Over the last two years, he has volunteered with Toronto Nature Stewards, tackling buckthorn at Roxborough and Leaside Parks, and for Don’t Mess with the Don, at their Sun Valley and Sunnybrook Park projects.

This article is intended for both a general audience and for Toronto Nature Stewards (TNS). Volunteers working for TNS must abide by regulations established by the City of Toronto.  This prevents them from using the most effective methods for managing large buckthorn infestations.

Why does buckthorn need bashing?

European buckthorn is an invasive species in Ontario. This means that it was introduced from elsewhere by humans, that has few pests or predators in its new location, that it can grow and spread aggressively, and that it is capable of displacing native Ontario plants. In this case, it was brought over from Europe as a shrub or tree that could create rapidly-growing dense thorny hedges. It grows quickly, in part because it stays green and growing long after native trees and shrubs have changed colour or lost their leaves. Buckthorn produces thousands of berries that are eaten by birds. The berries have little nutritional value and cause diarrhea in the birds. This encourages them to spread the seeds widely. A single large “mother tree” can produce thousands of seedlings spread over a fairly wide area. If left “unbashed,” buckthorn will quickly form dense monocultural growths, shading out all other species. Buckthorn is a threat to woodlands in large areas of central and eastern Canada and the north-eastern USA.

Buckthorns can be removed at any time of the year except in the depths of winter when they are hard to identify, and the ground may be frozen solid. Late fall (October and November) is often a convenient time as there are few other stewardship tasks that late in the year, and buckthorns can be highly visible as green plants amongst the fall colours.

Identifying buckthorn

The dark green, rather thick and glossy leaves are often easy to pick out, especially in late fall when other trees have fall colours or are already bare. The multiple glossy black or deep purple berries on female trees in the fall are very obvious. The leaves are arranged in an unusual “sub-pposite” arrangement. They neither alternate nor are they exactly opposite each other, but somewhere in between. There may be short thorns, especially where the branches divide. The veins on the leaves do not all radiate outwards from the main stem but rather curve back towards the central line as the leaf narrows. Some dogwoods have a similar pattern, so it is important to use other clues to be sure of the species before removing it. Buckthorn bark is pale, glossy, grey and becomes very shaggy and wrinkled in older trees. Scraping away the bark uncovers a very orange cambium layer.

How to bash buckthorn

Removing whole buckthorns

When possible, the best way to deal with buckthorn is to remove the whole shrub or tree. Very small ones (under two feet in height) can sometimes be pulled out by hand, especially if the soil is loose or wet. However, even small specimens may have strong root systems. It is often better not to strain your back, but to use a “weed wrench” such as the “Extractigator” instead. This device consists of a clamp that closes around the trunk of the buckthorn and a large handle that acts as a lever. Pushing down on the handle pulls out the buckthorn roots, completely pulling the plant from the soil. This is very satisfying and something volunteers enjoy doing.  If the roots are left exposed to the air for a few days, they will dry out and die, and that the plant cannot regrow. If there are no berries on the plant, it can safely be left on site in a bush pile or allowed to decompose on the forest floor.

Tips:

1) When removing a large buckthorn, it may be necessary to use the Extractigator to pull the plant in different directions to loosen the roots on all sides.

2) Cutting the trunk four or five feet off the ground can make pulling easier, but be mindful of any falling branches.

3) Another useful technique is to try to identify the main roots by close observation and digging with a trowel. The roots can then be cut with a lopper or a knife.

Buying weed wrenches such as the Extractigator and Pullerbear:

The “Extractigator” comes in a variety of sizes and can be ordered online from https://extractigator.com/. The standard or “Classic” has a handle that is 4 feet long, weighs 12.5 lbs, has a 2” wide jaw and sells for $169.99 Canadian (plus shipping). There is an even larger version that I have never seen used. There are two smaller versions. The “Junior” is only 3 ft long, weighs under 10 lbs, and is good for stems up to 1.5”. This is quite adequate for smaller buckthorn bushes, and the smaller size makes it more portable. The “Baby” has a 2 ft handle and weighs 7.6 lbs. The clamping mechanism is very similar to the other versions, but only takes 1 in wide stems. It works well for very small specimens, but the clamp mechanism is unduly large, making the “Baby” a bit heavier than would be ideal.

There is a “Bigfoot” attachment that bolts onto the base of the “Extractigator” and supports the fulcrum of the lever, especially in moist or uneven soil. I strongly recommend this for the Classic and Junior versions, but it would be “overkill” for the Baby version.

There is another make of weed wrenches, the Pullerbear. This is available from “Pullerbear Tree and Invasive Weed Pullers” at https://pullerbear.com/purchase.html). However, many people consider that they are not as well designed or built as the “Extractigator”, which they prefer.

Pruning buckthorn and “Critical Period Cutting.”

If trees are too large to be removed completely, then branches can be removed. This reduces the amount of water and nutrients that the tree will use, potentially slowing its growth, and lets more sunlight get through to the plants below. Removing and disposing of the berries prevents them from creating more seedlings.

Pruning may be preferable when removing the tree with all its roots would cause soil erosion. There are male and female plants, so the priority should be to remove berry-bearing female plants, preferably before the berries are ripe enough to grow if they fall off the branch. Berries should be removed and discarded of in landfill to prevent them ever growing. They cannot be treated as garden waste and composted, as this does not guarantee destroying the seeds. Sometimes buckthorns can grow 20 – 30 feet high, and the only practical way to remove berry-bearing branches is to cut down a large branch or trunk. This should be done very carefully to ensure that large branches do not fall on anyone. In some cases, a rope is useful. It can be tied around the branch above the proposed cut and used to ensure the branch falls in a safe and desirable direction.

One way of dealing with larger buckthorns is called “Critical Period Cutting.” The tree is tuned down to a 4 or 5-foot stump, and any new branches that are formed are removed several times per year, especially in spring and fall. This deprives the tree of energy of photosynthesis and uses up its energy reserves, eventually killing it after a few years, according to a group of Mississippi River Gorge Stewards.

Managing the cut branches or pulled trees

While small buckthorns without berries can just be left in place to rot, larger trees or branches need to be processed. This usually involves collecting them at a central location, preferably a paved parking lot or an area of mowed grass, where any discarded berries will not be able to grow. At this location, roots can be cut off and put aside for compost (as the City does not want to get soil in its wood chippers, and they do not burn well). Branches that have berries on them should ideally have the berries removed and only the actual berries put in the garbage for landfill, but in practice, to save time, they are usually cut into foot long lengths and bagged for landfill. The only alternative is to burn them (which is not within the TNS scope of practice). The branches without berries can be cut into about six-foot lengths and left on site as a bush pile (which provides shelter and habitat for some small animals), processed with a wood chipper, or burnt.

Pruned trees may grow back vigorously, so they will need continued monitoring and repeated pruning. A battery-powered hedge trimmer can be useful for this, but TNS volunteers are not permitted to use power tools.  There is a possibility that repeatedly removing all the branches from buckthorn may deny it energy from photosynthesis and eventually kill the tree.

Girdling (This is not within the TNS scope of practice)

Trees survive because water can flow up from the roots to the leaves in the xylem, and sugars can pass down to the roots for storage. These two structures form the cambium layer, which lies just below the bark. Cutting a circular groove about ½ inch (1 cm) deep all around the circumference of the buckthorn kills off the tree above the groove. This process is called girdling. It can be done with a hand saw, but a chain saw is better as it gouges a wider cut in the bark. There are four concerns about this approach. Firstly, many buckthorns have multiple stems, making girdling difficult. Secondly, the dead standing tree may be potentially dangerous. Thirdly, if the girdling cut is narrow the buckthorn may be able to repair it and survive. Finally, the buckthorn may regrow from below the girdling. Ideally, the buckthorn should be sprayed with herbicide at the level of the girdling to prevent regrowth, but TNS stewards are not allowed to use chemicals.

Cutting down buckthorn trees (This is not within the TNS scope of practice)

It is quite easy to cut down a mall buckthorn tree using a hand saw. Larger trees are easier to remove a battery-powered chain saw, but TNS volunteers are not allowed to use power tools. Once they have been cut down at soil level, they may then regrow from their roots unless the cut stump is sprayed with an herbicide such as Garlon or Roundup. Vigorous sprouting from an extensive root system can be cut back, but it is difficult to control except by applying herbicide.

An interesting new development is Lalcide Chondro,which is now available in Canada. It is currently registered as a biological herbicide for the inhibition of re-sprouting and regrowth from cut or girdled stumps of glossy and European buckthorn.

The active ingredient is Chondrostereum purpureum, a naturally occurring fungal plant pathogen. This is a hemibiotroph that infects living tissue, eventually killing it. It releases an enzyme which disrupts the middle lamella between the epidermal cells and palisade cells of the leaves causing the two layers to separate. This will control and inhibit stump sprouts post-harvest.

It is a biological solution that provides a more environmentally sensitive approach that may be useful for Toronto Nature Stewards and other groups that are not allowed to use chemical herbicides. There are several issues with this product. It is best applied in June or July when buckthorns are growing rapidly, but it is often more convenient to cut or girdle buckthorn in the late fall, when the tree is easier to spot. The cut or girdled tree does resprout after application of Lalcide Condro, but the new leaves are pale and look unhealthy. After about a year, when the sprouts may be one to three feet in length, they die. The treatment is effective, but the result does not look very pretty. The cost of the product is currently $75 per litre, and the whole litre container has to be used in one day. Purchasers need to have a license to use pesticides.

An alternative method of preventing regrowth is to leave a 4 – 6 inch tall stump, and then cover this stump with a light-proof barrier. This can be done using a thick black plastic bag, such as a “contractor” bag, or by using specially-designed “Buckthorn Bags”. These can be ordered online from  https://www.buckthornbaggie.com/. 100 Baggies and Zip Ties costs $114.99 + 59.99 S&H, making this a relatively expensive option. Regular thin plastic garbage bags are ineffective, as they are quickly broken and the buckthorn can pierce its way through (see top right picture below).

UPDATE: Make your own buckthorn bags

You can custom-make your own buckthorn bags to any size and shape you want.

Buy some 3m thickness contractor bags for about 50 c each.

Buy a 12-inch heat sealer from Amazon for about $40.

Cut the big plastic bag into whatever size you want – maybe 4 in wide by 6 in deep or 6 in wide by 8 in deep, depending on the size of the buckthorns. Seal the cuts, leaving only one open end.

Cover the stump with one bag and tie it in place with a zip tie ($16 for 300 from Amazon).

Add a second bag with the seal at 90 degrees to the first bag to ensure no right gets through. Secure with duck tape.

For added stealth, buy some camo-coloured Duck tape from Amazon for about $20.

If possible, I make a pile of discarded twigs and leaves around the stump, further increasing the blackout and hiding plastic, protecting it both from curious passers-by and from degradation by sunlight. I have found that this will usually remain in place for an entire growing season and prevent any re-sprouting from the base. I am not sure how long the bags need to remain in place before they can be removed safely, but one suggestion is that they need to stay in place for two years. The only real downside of this method is the labour involved and that the stumps can be a tripping hazard.

Herbicide (This is not within the TNS scope of practice.)

Buckthorn can be killed by spraying with an herbicide such as Glyphosate (“Roundup”) or Triclopyr (“Garlon”). This should be done with caution and respect to any surrounding vegetation. Both agents are absorbed through the leaves, but “Triclopyr” can also be absorbed through the trunk. In either case, repeated spraying may be needed. The dead buckthorn can either be left standing if this is safe, or felled once the herbicide has taken effect. As the buckthorn is already dead, so it will not resprout.

Biological controls

A biological control (i.e., an organism that could be released into the environment that would seek out and eat buckthorn) is under investigation but it is unlikely to be available for many years, if ever.

The Minnesota Department of Natural Resources thought that the most promising buckthorn-eating insects were three psyllid species (Trichochermes walkeri, Trioza rhamni and Cacopsylla rhamnicolla).

However, the psyllids caused low amounts of damage to common buckthorn.  Additionally, a plant disease was detected in the psyllids that could damage other plant species. After 11 years of searching for a biocontrol insect that is both host-specific and damaging to common buckthorn, they concluded that they did not have any promising agents at this time, so they ended the project.

The University of Minnesota scientists are studying whether any of the 17 known crown rust species are effective in damaging or killing buckthorn. However, I have noted that the buckthorns at Leaside Park are infected with a form of crown rust, but it seems to just discolour the leaves without causing serious harm. I am not optimistic that this approach will succeed.

Replanting

New evidence suggests that buckthorn berries only remain viable for one or two years after they have fallen to the ground, but birds may bring new seeds back to the site you have just cleared. Replanting the site with seeds, plants or saplings of desired native species will discourage the growth of new buckthorn seedlings, by reducing the light, water and other resources available to them. The denser the replating the more effective it will be.

Conclusion

Invasive European Buckthorn is a real threat to the woodlands of much of Canada and north-eastern parts of the United States. Left unchecked it can become dominant by forming a dense monoculture that crowds out native plants, shrubs and tree seedlings.

There are many ways that buckthorn can be controlled, but they all require some skill, considerable time and effort, and ongoing monitoring and maintenance. Fortunately, this issue is recognized by many people and organizations. For example, in Toronto, hundreds of volunteers have removed thousands of buckthorns from Toronto’s parks and public spaces, led by groups such as “Don’t Mess with the Don” and “Toronto Nature Stewards”. However, the effectiveness of these groups is limited by restrictions on their use of power tools and chemical herbicides. The City of Toronto should do more to support these and other volunteer groups.

Buckthorn is a real and ongoing threat to our native woodlands. Buckthorn bashing requires a cooperative approach in which government organizations do some of the heavy lifting, girdling or cutting large mother trees and spraying areas where buckthorn has become a monoculture while allowing, encouraging and supporting supervised volunteers to remove the smaller buckthorns and replant the new open areas with desirable and appropriate native species.

Further reading:

About Buckthorn:

Ontario trees and shrubs https://ontariotrees.com/main/species.php?id=2022 (Lots of pictures)

Toronto Nature Stewards’ Invasive Plant Information Sheet for buckthorn: https://drive.google.com/file/d/18id1qVU4Xd0ayhsb7W1bLLHF8dtkiyDA/view

From the Invasive Species Centre: https://www.invasivespeciescentre.ca/invasive-species/meet-the-species/invasive-plants/buckthorn/

From Ontario Invasive Plants: https://www.ontarioinvasiveplants.ca/wp-content/uploads/2016/06/OIPC_BMP_Buckthorn.pdf 

How to get involved in Toronto:

“Become a Steward” from Toronto Nature Stewards https://torontonaturestewards.org/get-involved/become-a-steward/

“Project Buckthorn” from “Don’t Mess with the Don” https://www.dontmesswiththedon.ca/project-buckthorn