Invasive Alien Plant Program
Figure 1: Leafy spurge – noxious weed and an invasive alien species.
The battle against unwanted plant invaders started soon after settlers came to Saskatchewan with a few seeds of their favorite plants from far away lands. While many were beneficial, some of these plants came to dominate crops, pastures and native areas and now cause serious economic and environmental harm. These invasive plants are also called weeds and are not wanted by agricultural, environmental or commercial land managers.
In Saskatchewan, the worst agricultural weeds are declared noxious under the Noxious Weeds Act (NWA). Section 13 (1) of the Act states: "Every owner or occupant of land shall destroy noxious weeds on his land and prevent the spread of noxious weeds to other lands."
The NWA, which has been in force in the province since 1909, empowers municipal governments to enforce noxious weed control by appointing a Weed Inspector as their enforcement agent.
Two important duties of a Weed Inspector are to enforce noxious weed control by private land owners and to prevent noxious weeds from spreading to new sites.
Among the weeds declared noxious under the Noxious Weed Act, leafy spurge (Euphorbia esula) is one that poses a serious threat of invading pastures and permanent grasslands. Leafy spurge (Figure 1 left) is a long lived, deep-rooted perennial plant that was introduced into Canada from Europe, and is now established in Saskatchewan and continues to spread; therefore, it can also be called an invasive alien plant species. There are many other plants that may or may not be regulated by either federal or provincial legislation that can be considered to be invasive alien plants. Each of these plants are in various stages of the invasion process, from introduction to adaptation, through expansion and then to widespread and naturalized.
In 1999, Thorpe and Godwin published Threats to Biodiversity in Saskatchewan, which examined the problem of exotic species invasion. From this report emerged Caring for Natural Environments: A Biodiversity Action Plan for Saskatchewan's Future (2004 to 2009) as a government-wide strategy to preserve the province's natural biodiversity. Invasive exotic species are animals, plants and other organisms that are not native to North America, Canada, Saskatchewan, or a particular natural environment. When introduced to a new area, they cause economic harm, environmental harm, and/or harm to human health. Objective 5.4 of the Biodiversity Action Plan states: "Identify and introduce measures to control populations of invasive exotic species existing in the province." Both documents identified invasive exotic species as a threat to biodiversity, and name leafy spurge as an example of an invasive exotic plant.
In Part Two, Section C (Environment) of the Federal-Provincial-Territorial Framework Agreement On Agricultural And Agri-Food Policy For The Twenty-First Century, there is agreement among federal and provincial governments that recognizes pest and biodiversity management. Two common environmental goals in the agreement are to "increase the use of beneficial pest and pesticide management practices" and "... promote compatibility between agriculture and biodiversity...." For dominating, aggressive plants like leafy spurge, this is difficult, but can be addressed in an agri-environmental farm plan by using integrated weed control to prevent spread to agricultural and environmentally-sensitive land.
Greater movement of materials, particularly grain and hay by road transport, has increased the opportunity for "hitch-hiking" weed seeds to drop and to establish new infestations on road right-of-ways. Eradicating weeds as soon as possible after introduction is better, both economically and environmentally, than waiting until they become well established before management begins. Some Rural Municipalities have passed truck tarping bylaws and bylaws restricting movement of hay from known areas where invasive alien plants such as leafy spurge are present, in order to restrict the transport and spread of the seeds of these weeds.
A leafy spurge seed can colonize a small area along a roadside in as little as four years, before it aggressively moves into the adjacent pasture or native plant communities. Horizontal roots spread the patch about 0.5 metres (m) per year, and viable seed can be catapulted up to 4.6 m from an established stand to new areas, via seed pods that pop violently when mature. Human activities move the weed even faster, moving weeds great distances in one event. Mowing of road allowances is often focused on issues not related to the spread of plants, such as snowdrift control or line-of-sight management. A simple change in the timing of mowing events, to cut areas with invasive alien plants at a very early flower stage, would prevent seed from these plants being dispersed as widely, as well as preventing the movement of weed seeds along the road allowance with the mower.
Figure 2: Solid line indicates small initial patch of leafy spurge and dotted line indicates extent of additional second year plants resulting from seed spread when seed pods in the initial patch erupt in a breeze. The drain in the foreground represents a risk of seed spreading greater distances in the drainage system. This seed spread could have been prevented by treating the small initial patch soon after establishment.
Leafy spurge is very competitive with range and pasture resources in Saskatchewan. When leafy spurge makes up 80 per cent of the vegetation cover, all grazing by cattle is eliminated because leafy spurge has replaced the grass cover. Cattle cannot eat leafy spurge due to the irritating and on rare occasions, toxic sap that circulates through the entire leafy spurge plant. Make no mistake: leafy spurge is a dreaded plant invader. Eradicating an introductory patch of leafy spurge which has moved into a new area is much more cost effective and requires less time and effort than trying to control an infestation once it is well established.
In 1999, the Noxious Weed Program was initiated to stop the spread of scentless chamomile, leafy spurge and other weeds because weed spread is such a threat to agriculture. The program was directed at weed inspectors, municipalities and landowners in the province.
Currently, the Invasive Alien Plant Program, funded as a pilot under the Canada-Saskatchewan Agri-Environmental Group Planning Initiative, began in 2006, and promotes development of long term weed management plans in addition to the integrated weed management activities begun under the Noxious Weeds Program. This new program promotes the use of modern methods of monitoring and managing invasive plants to prevent establishment and spread. Data collected by municipalities will be compiled and displayed in a map form, in order to outline the pathways that allow invasive plants to spread, and provide early warning to those municipalities that might not have a problem with a particular invasive plant.
The Invasive Alien Plant Program also continues to promote integrated weed management, which is a combination of non-conflicting control methods. Methods that can be integrated fit into the following categories: Physical, Chemical, Biological and Ecological. Physical control is manual pulling of weeds or mechanical removal of top growth by mowing. Chemical control is using herbicides to control or kill the weed. Classical biological control uses insects to attack and suppress a weed population and reduce its overall impact, although not eliminating the weed completely. Ecological control uses other desirable, yet competitive, plants to aggressively compete with weeds, or uses animals to graze weeds. The methods can be used at the same time or in sequence, depending on what has the greatest effect on the weed with the least impact on the environment and budgets.
The approach that local communities use to prevent weed spread should include all elements of Awareness, Education and Control of the weeds they are concerned about.
Awareness involves experts in the area of invasive plants and noxious weeds providing information to weed inspectors and the public regarding the danger of new invasive alien plant species and noxious weeds. An important part of awareness is weed identification. Education involves learning about the biology, ecology and control of the weeds you are aware of. Control is the integration of Biological, Chemical, Ecological and/or Physical methods, discussed above, to achieve the best results. The challenge is selecting the best method or combination of control methods.
Strategies used to prevent weed spread at the individual or community level should include elements of Exclusion, Eradication and Containment. Exclusion involves the use of quarantine to keep new and invasive alien/noxious weeds at far away locations. Knowing the contents of that seed lot or hay bale from outside the municipality, province or country is key to excluding new weeds. Eradication is the reduction of a population of weeds to zero. The best opportunity to attempt eradication is when an invader first arrives and occupies a small area on road right-of-ways. Use the best herbicide available. Remember, herbicide residue can be beneficial in non-crop areas, except when there is a risk of environmental damage. Herbicide residues help to prevent the regrowth of weeds, but if used in environmentally sensitive areas, such as sandy soils or high water table areas, herbicide residues can move into groundwater. Once a weed becomes established, it is no longer economical or possible to eradicate, and weed control moves into the "containment" phase.
Figure 3: This is when eradication should be used for leafy spurge.
Containment means keeping a weed population within a specific area. Public awareness allows weed inspectors and landowners to quarantine areas with known invaders. Should eradication of a new weed fail, move on to develop a containment program to prevent spread of the weed. Containment is usually establishing a boundary, beyond which the weed will not be allowed to move. Inside that boundary, integrated management methods are used to reduce the overall impact of the weed and to reduce the opportunity for the reproductive parts of the weed to spread. Figure 3 shows a fairly new patch of leafy spurge that is colonizing and should be eradicated. This is not easy, because some seed may have been catapulted from the site, and seed can remain viable in the soil for at least eight years.
Figure 4: This is when leafy spurge should be aggressively contained and controlled within the containment area (arrow shows the direction of leafy spurge movement).
The procedure to manage a weed to prevent spread involves 1) scouting for the weed, 2) controlling the weed using integrated weed control and 3) monitoring for success. Marking the location of a known invader site, as a waypoint in a GPS receiver, has greatly enhanced the procedure to control weeds. Figure 4 shows leafy spurge aggressively moving in the direction of the arrow. This weed population should be contained before it can spread further.Through the Invasive Alien Plant Program in Saskatchewan, weed inspectors are encouraged to aggressively eradicate small patches of leafy spurge (Figure 3) and other invasive plants, and contain established weeds within large areas (Figure 4) while introducing integrated management elements into the contained area, to minimize the impact of the weed.
Anonymous. 2003. Federal-Provincial-Territorial Framework Agreement on Agricultural and Agri-Food Policy for the Twenty-First Century Part. Two - Chapter Components of the Framework Agreement. Section C - Environment.
Government of Saskatchewan. Date unknown. Caring for Natural Environments: A Biodiversity Action Plan for Saskatchewan's Future 2004-2009.
Thorpe, J. and B. Godwin. 1999. Threats to Biodiversity in Saskatchewan. SRC Publication No. 11158-1C99.
Government of Saskatchewan. 1984. The Noxious Weed Act, 1984 . Available from Queen's Printer, Province of Saskatchewan.