Eurasian Watermilfoil – Dealing with the Threat

The FLCA was fortunate that in 2018, the Ontario Trillium Foundation, an agency of the government of Ontario, approved our application for a grant to help us with our efforts to control the spread of Eurasian Watermilfoil (EWM) in Farlain Lake for three years covering the period ending 2021!  Due to COVID restrictions and our inability to fully implement our management plan in both 2020 and 2021, the period was extended to the end of 2022.  Over the past five years, we have worked hard to develop strategies to control the infestation of this very aggressive aquatic plant based on extensive research, consultation, networking and experience. The grant will help provide us with the resources we need to purchase equipment, supplies and services needed to manage the EWM and protect the future of our lake.  It’s hoped that our learning and experience will also help other communities dealing with the EWM.

What is the Eurasian Water Milfoil (EWM)?

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.

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. To manage EWM and improve the lake’s water quality in Puslinch Lake Ontario, through dredging the annual operating cost is approximately $150,000.

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.

2019 EWM Control Project

Unfortunately, 2019 was the last year we were able to fully implement the integrated management strategy described above.  The following provides a detailed picture of all that is involved in the project in a typical year.

Once all necessary permits/permissions were obtained from Department of Fisheries and Oceans Canada (DFO), Ontario Ministry of Natural Resources and Forestry (MNRF), and the Ontario Ministry of the Environment, Conservation, and Parks (MECP), the full work plan consisted of the following:

• Weed Watcher Recruitment and Training
• Mapping the Infestations
• Preparation of Equipment and Materials
• Application of the Herbicide
• Recruitment of Volunteers for Harvesting
• Application of Bottom Barrier Mats and Harvesting
• Evaluation

Weed Watcher Recruitment and Training

In partnership with the SSEA, a shoreline workshop educated volunteers in aquatic plant surveying/mapping/monitoring. A Weed Watcher Training Manual has been developed to provide a basis for educating our volunteers in the identification of not only the EWM but other aquatic plants. OTF funds have been used to purchase surveying/mapping/monitoring equipment (e.g. hand held GPS units, range finders, depth finders, underwater cameras, sampling rakes, marker buoys, etc.) required for the surveying/mapping/monitoring of the EWM.

Mapping the Infestations

The key to effective management of EWM in Farlain Lake is to locate EWM plants and prioritize control efforts. As we lack sufficient funding to undertake control efforts on a weekly basis throughout the summer months, our management efforts must be based on realistic, cost effective, and ecologically sound control efforts. Our strategy is to reduce the size of dense mature EWM infestations and to remove new small EWM plant infestations in high risk areas.

Mapping is a critical step in not only identifying where the infestations exist, but in our ongoing evaluation and reporting of the outcome of our control efforts. FLCA volunteers will be conducting extensive surveys of the lake to search for EWM plants. Working from the FLCA pontoon boats and other watercraft, the FLCA will locate EWM infestations, mark them with floating buoys, and map them for management priority setting. The SSEA prepared a set of study sector maps requested by the FLCA. The maps denote GIS images, bathymetry lake contour data, and study sector research grids. The mapping is repeated at the end of the season as part of the evaluation of our efforts.

Preparation of Equipment and Materials

Funding provided by the Ontario Trillium Foundation has enabled the FLCA to purchase and equip a second pontoon boat to be used as a support vessel for our DASH (Diver Assisted Suction Harvesting) pontoon boat. So we now have Trillium I and Trillium II! The second pontoon boat will also be equipped for use in mapping/monitoring aquatic plants, and community outreach and education. Modifications to both boats, procurement of materials such as containment curtains for harvesting, sand bags, safety equipment, etc. are all part of the preparation.

In addition, contracts were completed for the various services needed such as the professional divers and licensed applicators for the herbicide.

Application of the Herbicide

Application of the aquatic herbicide Reward took place by licensed applicators between mid and end of July in order to avoid fisheries spawning and incubation. Application was very targeted only to specific infested areas and due to the fact that the herbicide is heavier than water, it does not spread. It also does not kill the plant but simply temporarily suppresses the growth. It is absorbed by targeted plants in just minutes with no toxicity to fish or wildlife. Swimming in the application areas is restricted only for one day as a precaution. Permission was sought from property owners within 200 ft. of the area to be sprayed.

Recruitment of Volunteers

Volunteers are needed for weed watching, preparation for the harvesting and the harvest. Details of tasks and timelines will be in a call for volunteers once confirmed.

Harvesting and Application of Bottom Barriers

Harvesting and the laying down of benthic mats took place over two weekends in August. Base camp was located at the Sweenie Farm on the southwest of the lake. Harvesting utilized FLCA’s DASH system, volunteers, and contracted commercial divers to remove the plant from targeted infested areas based on the mapping. In other areas, plants are cut and then covered with bottom barriers held down with sand bags. Barriers and bags will decompose over time.  Containment curtains were installed around areas to be harvested and where bottom barriers were to be installed.

Evaluation

An important step every year is the evaluation of all the strategies employed over the summer. This consists of additional surveying following the August harvesting and feedback from participants through a focus group. The results are provided to the FLCA members, SSEA, Township and included in a formal report to be submitted to the Ontario Trillium Foundation in December to ensure the continuation of funding for the second of the three years of the grant.

The FLCA is happy to share our experience and further details with other communities in Ontario who may be dealing with this very aggressive aquatic plant. Simply contact us through our email at inquiries@farlainlake.ca

2020 EWM Control Project

Sadly, as with so many other things, the COVID pandemic severely curtailed our efforts in 2020 and all we were able to undertake was one of the components of our management plan – the application of the herbicide Reward. Since it was all we were able to do other than mapping and monitoring, we added a second application of Reward as well as a 10 m buffer to the various sites of infestation. That combined with good weather conditions on the two days of the application resulted in some success, more so than previous years as far as the herbicide was concerned. Although we couldn’t lay any more bottom barriers down given the physical restrictions resulting from COVID19, we were able to review the sites where mats had been laid down in previous years and were pleased with what we found in terms of the impact on the EWM. I’ve also attached the assessment report for the work we did this year.The initial work plan had to be significantly modified as a result of the pandemic and the subsequent restrictions on gatherings and activities and the need to keep everyone safe. The only control method used this year was the application of the aquatic herbicide, Reward. In consultation with the SSEA, it was decided to add a 10 metre “buffer zone” around each of the infestation sites to allow for any “drift” in the water column as the herbicide sank, and to add a second application in an attempt to improve the impact of the herbicide but with a two week separation to mitigate any harm to the fishery and invertebrates in the targeted treatment area. Ten sites were treated.

Information on the herbicide and the treatment plans were shared with FLCA members in the spring and early summer. Shoreline property owners within 200 ft of the targeted areas were notified of the plans and precautions re swimming and use of the lake water immediately following the application. Volunteers marked each of the sites with buoys, signage was posted at the boat launch and floating signage was placed within each of the offshore sites. Spraying was completed by the licensed applicator, Peerless Turfcare, on July 16 and July 30. Since then, EWM Committee members and diver friends of Farlain Lake have been monitoring the infestation sites and collecting data in order to assess the impact of the herbicide as well as review the sites treated with bottom barriers in previous years.

A report on the results of our efforts this year was prepared by Pete Andrews based on input from our EWM team members Members Lory Brouillette, Greg Goss, Don Ferguson, and Brian Kelso along with friends of Farlain Lake, professional diver Jim Zacher and Dr. Michael Jenken (York University). The following is an excerpt from that report – you can download the full report with details on the results for each of the infestation sites included in the Appendix. [insert PDF] The report was submitted to the MNRF, DFO and MECP, and shared with the SSEA in preparation for planning next year’s project.

Our review indicates that the EWM population in Farlain Lake persists in spite of previous management efforts. However, the FLCA EWM control program has made significant progress over the course of the multi-year integrated invasive aquatic plant management project that began in 2019. A total of 5,660 m² (0.5 hectare) of targeted plants were treated with Reward in 2020 of which 4,764 m² (0.48 hectare) was deemed to have good to excellent EWM control. The sites are deemed to be effectively managed were the Andrew Drive, South West Corner, W-J, South of the Colony, Pioneer Colony, and the Lakeview sites. Reduction in EWM in the Pioneer and Lakeview Sites cannot be attributed solely to the treatment of EWM with Reward; these sites were previously managed with jute bottom barrier in 2019. The treatment of EWM with Reward has reduced the overall density of EWM in the lake thereby mitigating the spread of the invasive aquatic plant throughout the lake.

The treatment with Reward on 877m² (0.9 hectare) of the total area sprayed was considered to have limited control. These sites included the Parkette, Timcourt, Saltwater Pool, and the North End sites. The limited control of EWM by herbicide treatment in the North End could be attributed to the characteristics of the herbicide. Reward becomes adsorbed by clay particles or organic matter. The location of the North End site is in deep organic muck. There is a possibility that the movement of the herbicide applicators’ boat in the shallow water stirred up the bottom mucky substrate creating turbidity in the water. The aquatic herbicide bonded to the soil particles in the water column reducing the amount of chemical taken up by the aquatic plants. The offshore locations and shape of the Timcourt and Saltwater sites likely contributed to the limited success in managing EWM in the dense intermixed (native and non-native plants) infestations. While the south part of the Parkette site was partially successful in managing EWM, the north part of the infestation (nearest the boat launch) was least affected by the treatment. The reasons for the limited control on the north end of Parkette site are unknown.

Compared to previous years treatment with Reward, the plants in the sites that were deemed to have good to excellent control, showed a significant decrease in biomass volume. This can be attributed to two treatments each year as opposed to a single treatment. The success of managing EWM in these sites demonstrates the sensitivity of EWM to Diquat dibromide. It also appears that some native species (e.g. large leaved pondweed, tape grass) are more tolerant to Reward than other native species.

The use of Reward as a singular control method will not manage the EWM populations in Farlain Lake alone. The aquatic herbicide must be used in a strategic integrated manner with other viable control methods. Through an integrated management approach, the amount of effort to manage EWM in Farlain Lake will lessen over time.