Eurasian Watermilfoil – Dealing with the Threat
Our Story Begins
Eurasian Watermilfoil (EWM) is an extremely aggressive non-native invasive water plant that forms thick underwater stands of tangled stems and vast mats of vegetation on the water’s surface, especially in shallow lakes like Farlain Lake. It was discovered in Farlain Lake in 2012 during a FLCA aquatic plant study of the lake. It had not been observed by Ontario government organizations studying water quality or the fisheries of the lake prior to that. The pioneer colony (original infestation) was limited to a small isolated area less than one acre in size on the southwest shoreline of the lake. Over subsequent years, the plant spread to the point where 18 sites of varying size and density were identified throughout the lake.
EWM is considered one of the most widely distributed aquatic invasive species with records of EWM confirmed in 47 continental USA states as well as the provinces of British Columbia, Ontario, and Quebec. Various organizations have been combatting EWM for years. For example, Lake George in New York State’s Adirondack Park has been managing EWM for 32 years. The Okanagan Basin Water Board in British Columbia has been combatting EWM for the past 40 years. Control budgets vary depending on the severity of the problem and the size of the water body. For example, the Christina Lake, British Columbia, EWM control program is $213,000 annually.
EWM will grow from plant fragments created from physical breakage by boaters, anglers, and other disturbances (e.g. forceful wave action, aquatic animals, fish, waterfowl, etc.) during the summer months. In late fall during the end of its growth period EWM becomes brittle and naturally break apart. Plant fragments are the primary means of EWM reproduction; they float on the surface and are dispersed by wind and wave actions to other areas where they sink and colonize into new plants. In optimum water temperatures (15°C – 35°C) EWM plants can grow 30 cm per week.
Why is EWM a Problem?
EWM is an extremely aggressive invasive aquatic plant that forms thick underwater stands of tangled stems and dense floating mats of vegetation.Some of the problems associated with EWM include:
Recreational activities such as boating, fishing, and swimming are impeded by dense growth at or near the surface.
Shoreline property values can be de-valued. EWM choked bodies of water can depress real estate values up to 20%.
The lake’s ecosystem will be altered. EWM will displace important native plants thus harming fish and wildlife habitat. Dense floating vegetation becomes breeding habitat for mosquitoes.
Stagnant oxygen-depleted conditions are often found in association with dense beds of EWM. Sudden nutrient release caused by late-season die-back of extensive plant beds may cause nuisance algae blooms.
Costs to manage EWM growth are borne by either local citizens, lake management organizations, and/or local governments.
FLCA’s Efforts to Manage the EWM
The FLCA implemented a EWM Control Program in 2014 under the leadership of the EWM Team working with the FLCA Board, and with the support of many volunteers from the community. We also appreciate the ongoing support we received from the Severn Sound Environmental Association (SSEA) and the Township of Tiny.
Our strategy to manage the Eurasian Watermilfoil was developed over the years since its discovery by a dedicated team of volunteers who spent countless hours researching possible options, developing plans each year and seeking the resources needed to implement the plan. The EWM Steering Committee was responsible for working with the FLCA Board on an EWM Integrated Management Plan annually which has formed the basis of our annual control efforts. In the early years of our efforts, that plan essentially included three components: 1) application of the herbicide Reward, 2) installation of benthic mats (bottom barriers) in infested areas, and 3) manual harvesting using DASH (Diver Assisted Harvesting). All of these components required authorization from various government agencies (Department of Fisheries and Oceans, Ministry of Natural Resources and Forestries, and the Ministry of the Environment, Conservation and Parks).
Each year we reviewed the outcome of our efforts and developed a work plan for the following season based on our assessment at the end of the season. In 2018 we were fortunate in obtaining a sizeable grant from the Ontario Trillium Foundation (OTF) to fund equipment, supplies, etc. which provided much needed resources through to 2024. Unfortunately, despite our best efforts, the plant continued to spread through the lake and as of 2022, our efforts seemed to be useless. However, through ongoing research, we became aware of a new herbicide called ProcellaCOR which had been developed and used very successfully since 2018 in the US to eradicate the EWM in a number of lakes. Health Canada, through its Pesticide Management Regulatory Agency, PMRA, conducted a review of an application for the use of the herbicide in Canada starting in 2019 and registration was finally granted in May of 2023.
The Introduction of ProcellaCor FX
While awaiting the outcome of the Health Canada review of the new herbicide, ProcellaCOR, the FLCA proceeded with the submission of approval for its application to the DFO, MNRF and MECP in early 2023. We received approval to proceed with the application of ProcellaCOR to the infested areas in Farlain Lake following extensive communication with these agencies in August 2023. The application of ProcellaCOR FX (the Canadian version) was completed on September 6, 2023 by a US based lake management company since there were no Canadian companies licensed to apply this new herbicide at the time. This was the culmination of over 6 months of ongoing, relentless communication with DFO and the MECP by our EWM Team.
About ProcellaCOR and the Treatment Application
Preparation
Shoreline property owners near the infestation sites were notified of the plans for treatment and no major concerns were received. The FLCA used elerts, signage and Facebook to communicate plans to members. Members of the community were invited to send any comments, questions or concerns in to us at the FLCA general email box at inquiries@farlainlake.ca.Buoys marking the sites to be treated were placed on the lake a few days in advance of treatment. The markers were removed immediately following the application. The EWM team reviewed all the sites and took images with our underwater drone to establish a baseline for the purpose of evaluating the effectiveness of the herbicide.
The application of ProcellaCOR must be done by a licensed applicator specifically trained for this particular herbicide. Farlain Lake was the first freshwater lake in Canada to be approved for the application of ProcellaCOR FX since its approval by Health Canada. The application also requires particular equipment as seen in this photo taken during the treatment on Farlain Lake.
Advisory Recommendations for Lake Water Use Following Treatment
- Do not use treated water for irrigation of greenhouse vegetables and fruits;
- Do not use treated water for hydroponic irrigation without activated charcoal or similar filtration.
- Do not use treated water for irrigation of residential gardens, turf grass, landscape vegetation or other non-food irrigation for 5 days after application.
- Do not use treated water for irrigation of commercial field crops until concentrations are analytically below 2 ppb.
What to Expect Following Treatment
The Results
Approximately 4 weeks later on October 4, the EWM team and Dr. Heilman reviewed the treated sites, checking the status of both the invasive plants as well as the surrounding native plants. Many photos and videos were taken during the treatment. The findings more than met expectations – the EWM was dying and the native plants appeared untouched and healthy as seen in these two photos taken that day.Since then a very comprehensive report was completed thanks in particular to Peter Andrews with input from our EWM team and Dr. Heilman. The FLCA 2023 EWM Management Year End Report can be downloaded here. SOLitude also completed a report for submission to the MECP as required. Farlain Lake is the first inland lake in Canada to be treated with the newly registered ProcellaCOR FX by a licensed applicator certified by SePRO for ProcellaCOR FX.. SePRO has produced a video reflecting our project as part of its Lakes and Ponds Heroes program.
The work didn’t stop there. The 2024 work plan was submitted to DFO and MECP based on the 2023 project and results seen in the fall. Approval was received for the application of ProcellaCOR again in 2024 if needed. The Farlain Lake 2024 EWM Integrated Management Plan Final is available here to download for your information.
Our EWM team was out in May of 2024 to survey the sites. We were thrilled to find that there was no sign of the EWM at any of the sites and that the native plants appeared untouched. A SOLitude biologist returned to the lake in July and conducted a thorough review of the sites and confirmed no presence of the EWM. In addition to surveying the vegetation using a rake toss method, native plants were identified and recorded, a temperature (temp) and dissolved oxygen (DO) profile was collected at four sites (4, 8, 9, 17), per DFO requirements. The oxygen levels were normal or higher. The results of that review are documented in the formal report available for downloading FarlainLake2024_Report_Final.
Current Status
The FLCA will continue its monitoring of the lake for any sign of the return of the EWM. On our first inspection in the early spring of 2025, we did visual and rake toss inspections of the previously treated 17 EWM sites were completed. At that time, things were a little more difficult to see due to the turbidity caused by rain and winds and runoff. However in July, John Boidosik of SePRO (ProcellaCOR FX supplier and developer) came to the lake and with our team, carried out another inspection The inspection was visual as well as underwater using the FLCA drone camera and a physical rake toss inspection of all of the previously treated EWM areas. All sites except one showed no evidence of EWM and healthy native plants were intact and thriving. Unfortunately, there was one area, at the mouth of the incoming stream at the southwest end of the lake where a very small infestation of a few EWM plants was found. In the latter part of July, another inspection took place with Solitude Lake Management as part of their last contracted inspection. The results of Solitudes’ investigation were the same, finding no growth of EWM except a small amount at the previously mentioned location.
Since then, the necessary permits and approvals were carried out by the EWM Committee and a permit to treat that one area was issued later in August. Because ProcellaCOR FX was approved for use in Canada in 2023, there are now applicators in Ontario that have been approved by SePRO and are licensed in Canada. A spot application was completed in September by a Canadian company out of Hanover, ON.
The EWM Committee will continue to monitor the status and treatment of this area as well as the previously treated ones. The Ontario Trillium Foundation grant final report was completed in 2025 and we will always be extremely appreciative of the grant for providing the resources that ultimately led to success in managing this aggressive invasive plant. We remain vigilant and are optimistic with regards to the success we have experienced these past few years battling the EWM.
The FLCA is happy to answer questions and provide additional information to share our experience with others battling this invasive plant. Simply contact the FLCA via email at inquiries@farlainlake.ca and we will respond as quickly as possible.