Weeds, also referred to as invasive plants, are “non-native plants that adapt quickly and aggressively to the landscape causing lasting damage.”[1] Invasive weeds are generally undesirable where they are found, outcompeting native species and disrupting the provision of ecosystem services that the native species contribute to.
Biological weed control utilizes “a natural predator or pathogen of weeds”[2] and can include the use of fungi, bacteria (bioherbicides) and insects to control targeted weed species without the negative environmental and human health effects that may be associated with the use of chemical herbicides. Inundative biological control is a short-term treatment with fungi or rusts and is species-specific to targeted weeds. Classical biological control is a longer-term and often self-sustaining “rebalancing” of insects or mites that attack specific weeds.[3]
Physical/mechanical weed control can include manual pulling of weeds and targeted grazing by livestock to control specific weed species.
Municipalities seeking to limit or reduce use of chemical herbicides and reap the health and water quality benefits of doing so can employ this nature-based solution to manage weeds in public spaces.
Recommended Practices
An integrated approach uses mechanical and biological weed control and aims to reduce the seed bank of weeds in soil, minimize the growth of weeds and limit the extent to which weeds outcompete desirable species of plants.[4]
Managing soil for weed seed banks. Combining tillage to limit germination with the application of bioherbicides can reduce the seed bank of weeds in soils.
Mechanical/physical weed control. Removing young and established weeds before they go to seed is an important aspect of integrated weed management. This can be done by hand pulling, machine-assisted weed removal and the use of targeted grazing by livestock.
Mulching. Spreading mulch (organic or synthetic) over small areas helps to inhibit germination of weeds.
Increase desirable species’ competitive abilities. The application of bioherbicides, targeted grazing and pathogenic insects that attack weeds can help desirable species better out-compete weed plants and prevent the weeds from becoming established. Choosing crop cultivars that are more likely to successfully compete with weeds when planting a disturbed area is important.
Managing herbicide-resistant weeds. Undesirable weeds may become resistant to chemical herbicide treatments. In this case, use of biological controls, targeted grazing and mechanical weeding can provide a strong alternative to chemical herbicides.
Use of targeted grazing on slopes and near water bodies. Because of the potential impacts to water quality and human health of chemical herbicides, targeted grazing by goats presents a viable alternative on slopes and in close proximity to bodies of water.
Monitoring. Ongoing monitoring can help identify weeds early and helps to determine the efficacy of previous and current weed management strategies.
Project Considerations
Legal obligations. In Alberta, the Weed Control Act states that weeds classified as noxious must be controlled and those classified as prohibited noxious weeds must be destroyed.
Engaging stakeholders. Managing weeds on public lands or within new developments typically entails engaging many stakeholders. Municipalities and developers looking to practice integrated weed management should include policy makers, weed scientists, land managers and the public in the process.[5]
Long-term process. Managing weeds is a long-term process. Herbicides may be effective in the short-term over small areas, but biological and other controls included in integrated weed management are recommended for larger areas and over the long-term.[6]
Potential negative impacts. Some fungal pathogens that can be used as biological controls for weed management also produce toxins that can affect mammals and therefore should be studied carefully before application is considered.
The Business Side
In certain situations, biological weed control and targeted grazing can be more cost-effective than chemical control[7] and are ideal management approaches near water and aquatic ecosystems as well as slopes and forested areas. If done well, classical biological control can be self-sustaining; there may be a reduced need for ongoing applications of weed control.
The Nature Side
Biological controls and targeted grazing leverage natural processes to manage weeds, allowing for a reduction or elimination of use of herbicides that can pose risks to water quality, soil health and human health. This example of NBS manages weeds selectively and helps desirable plants such as native species to thrive rather than being outcompeted by weeds. There are minimal environmental impacts to these methods of weed control and, in the case of targeted grazing by animals, nutrients are added to the soil in the form of manure. Effective integrated weed management can improve biodiversity of native species and increase the ecosystem services that are provided.
The Community Side
Using biological controls for weeds and targeted grazing can improve public safety by reducing or eliminating chemical herbicide use, as the most common commercial herbicide (glyphosate) is classified as a probable human carcinogen.[8] Residents can enjoy the overall aesthetic benefit of weed control. Eliminating weeds that can cause injury or irritation (such as thistles or giant hogweed, respectively) can also allow for increased recreational opportunities in places otherwise overtaken by these plants. Citizens can get involved in volunteer weed pulls and targeted grazing initiatives provide the opportunity for public education.
[1] Government of Alberta. 2021. Weed control. Government of Alberta.
[2], [4] Bo, A. B., Khaitov, B., Umurzokov, M., Cho, K. M., Park, K. W., & Choi, J. S. 2020. Biological Control Using Plant Pathogens in Weed Management. The Korean Society of Weed Science and The Turfgrass Society of Korea.
[3], [7] New South Wales Government. Integrated weed management. NSW Government.
[5] Bagavathiannan, M. V., Graham, S., Ma, Z., Barney, J. N., Coutts, S. R., Caicedo, A. L., De Clerck-Floate, R., West, N. M., Blank, L., Metcalf, A. L., Lacoste, M., Moreno, C. R., Evans, J. A., Burke, I., & Beckie, H. 2019. Considering weed management as a social dilemma bridges individual and collective interests. Nature Plants 5 (343-351).
[6] Binzen Fuller, K. & Mangold, J. 2017. The costs of noxious weeds: what you can do about them. Big Sky Small Acres.
[8] Pesticide Action Network Europe. 2017. Alternatives to herbicide use in weed management – The case of glyphosate and other herbicides. PAN Europe.
Bagavathiannan, M. V., Graham, S., Ma, Z., Barney, J. N., Coutts, S. R., Caicedo, A. L., De Clerck-Floate, R., West, N. M., Blank, L., Metcalf, A. L., Lacoste, M., Moreno, C. R., Evans, J. A., Burke, I., & Beckie, H. 2019. Considering weed management as a social dilemma bridges individual and collective interests. Nature Plants 5 (343-351).
Binzen Fuller, K. & Mangold, J. 2017. The costs of noxious weeds: what you can do about them. Big Sky Small Acres.
Bo, A. B., Khaitov, B., Umurzokov, M., Cho, K. M., Park, K. W., & Choi, J. S. 2020. Biological Control Using Plant Pathogens in Weed Management. The Korean Society of Weed Science and The Turfgrass Society of Korea.
Government of Alberta. 2021. Weed control. Government of Alberta.
New South Wales Government. Integrated weed management. NSW Government.
Pesticide Action Network Europe. 2017. Alternatives to herbicide use in weed management – The case of glyphosate and other herbicides. PAN Europe.