Native to Europe, common buckthorn (Rhamnus cathartica) is often referred to as European buckthorn. With allelopathic qualities, aggressive reproduction, and prolific growth, buckthorn can quickly outcompete native forest understory and create dense, even-aged stands. Their berries, consumed by many bird species, provide little nutrients, and are quickly excreted, contributing to further spread. With its invasive characteristics, thorns on its stems and a host to many pathogens, buckthorn poses negative impacts to the environment, society, and economy. As a result, land managers are battling the buckthorn infestations threatening forests and agricultural lands across North America.
In Canada, the Pest Management Regulatory Agency is responsible for pesticide regulation. The pesticide label outlines who can use a pesticide, and under what circumstances. Pesticides under federal regulation are organized into four classes, based on where, when and by whom they may be applied. In many cases, manual remove techniques are employed to help control and manage invasive species when other options are not appropriate or available.
Management options to tame this aggressive invader include both manual and chemical control. The appropriate and effective control methods for each infestation may vary depending on the size and density of the population and stem diameters of the plants, as well as site characteristics. For example, some site characteristics to take into consideration are the sensitivity of the area, species at risk, or site accessibility, to name a few. The Ontario Best Management Guide outlines seven control options in detail to help land managers decide the best management strategy for a particular infestation. The most common mechanical control option is pulling buckthorn stems. Smaller stems up to one meter in height can be successfully hand pulled, especially in moist soil. There are tools, such as weed wrenches, to help remove stems approaching sizes up to 5 cm in diameter. For larger stems, some have found success using tractors to pull the stem and roots out of the ground. The removal of medium to large sized stems and roots leave large holes behind that require filling and replanting. Pulling is recommended for Fall months as buckthorn leaves stay green longer making identification easier and ground vegetation has gone dormant reducing non-target disturbance. If berries are present at time of management, it is also suggested to remove and bag berries to limit their spread to disturbed soils.
In areas of dense seedlings less than two years old, mowing repeatedly in early to late summer can reduce numbers and vigor of new seedlings. Seedlings are also acceptable food for livestock making grazing another option. Mowing and grazing, however, are not target specific and prevent the growth of other vegetation. More limited control methods covered in the Best Management Guide include fire and flood for specific scenarios.
Cutting buckthorn stems is not recommended without the use of herbicides or baggies as invasive woody species sprout and sucker, increasing the number of stems and exacerbating the situation. Baggies are specific black, robust bags used to cover and smother stems as well as potential new shoots. This method decreases soil disturbance and non-target species damage, also decreasing chances for buckthorn seeds in soil to germinate.
Removing buckthorn without a remediation plan will leave the area susceptible to new buckthorn growth from the soil seedbank and establishment of new invasive plants that will take advantage of disturbed soil. Consider replacing the removed buckthorn with native plants to increase chances of success for long-term management. Planting the area with native species (grasses, herbs or woody plants) can fill the space left behind and smother out new buckthorn growth while also limiting opportunities for new invasions.
This article was contributed by Derissa Vincentini, Community Science Coordinator with the Invasive Species Centre. The Invasive Species Centre prevents the introduction and spread of high-risk invasive species in Canada by connecting stakeholders with knowledge and technology.
