Eurasian milfoil (Myriophyllum spicatum) is a perennial aquatic plant that lives submerged between 0.5 and 4 m deep. The plant takes root at the bottom of the lake and grows to the surface where it branches and forms dense beds. Originating from Europe, Asia and North Africa, it adapts to a variety of different environments, which makes it very invasive.
The proliferation of milfoil in a body of water has several consequences from an ecological, recreational, health and land perspective. Milfoil competes with native plants for light and nutrients. This leads to a loss of biodiversity in streams and water bodies. The small beds of milfoil can serve as shelter for aquatic fauna. Dense beds, on the other hand, can alter food chains and reduce dissolved oxygen. This can replace spawning sites and promote the proliferation of mosquitoes. Large colonies of Eurasian milfoil interfere with recreational activities such as boating, fishing and swimming. Properties and homes around an infested lake may also depreciate and sell for less.
We have noticed that Eurasian milfoil is developing very rapidly in Quebec's rivers and lakes. This plant invades the littoral zone of the lake forming an almost continuous crown of monospecific and mixed beds of milfoil. Note that the littoral zone of a lake is a band around the lake generally covered with vegetation. It extends into the lake and is a very productive environment where aquatic plants and spawning grounds are found. As a result, the threats represented by this invasive plant must be evaluated according to the littoral zone of the lake and not according to the entire lake itself.
In 2015, we surveyed 13 lakes totaling an area of approximately 3000 ha to assess the coverage of the littoral zone by Eurasian milfoil (Table 1). Considering only the monospecific beds (composed of at least 80% of milfoil), we found that currently the Eurasian milfoil covers in average 30% of the littoral area of the lake. In the future, if no control measures are taken, mixed milfoil beds will develop into monospecific ones and then the percentage of littoral cover will reach an alarming value of 45%.
The situation then requires strict and effective measures to slow the invasion of this vital area of the lake by milfoil. Although preventing the introduction of Eurasian milfoil is the best way to control this invasive species, several methods of control were evaluated. Mechanical methods such as manual or mechanical cutting and pulling can promote the spread of Eurasian milfoil and threaten native flora. Biological control shows that there are several insects known to help manage Eurasian milfoil infestations such as Eurychiopsis lecontei and Cricotopus myriophylli. Despite the availability of such natural enemies, the insects used need to be compatible and present at a high density to show an adequate control.
Recently, the use of a biodegradable jute material to eradicate invasive aquatic macrophytes has been proven. The use of burlap was tested in Ireland by a researcher on an exotic and invasive aquatic plant, Lagarosiphon major Ridley de Lough Corrib (Caffrey et al., 2010). The study found that burlap, unlike a geotextile fabric, is biodegradable and allows native plants to grow through. As a result, this study shows that this material has potential for broader application in the management of aquatic weeds and in the restoration of native flora.
The ABV des 7 replicated this experience at Lake Pémichangan (MRC La-Vallée-de-la-Gatineau) in April 2012. After five years of installing burlap at Lake Pémichangan, the results are similar to those obtained in the Irish study and the balance of the aquatic ecosystem of Lake Pémichangan returned to its normal. The advantage of using burlap is that it is made of a biodegradable material that will deteriorate in 1 to 3 years; it allows recolonization with native species and it does not require maintenance other than its installation and recommended annual monitoring.
Steps to follow for the installation of burlap:
The report on the control of Eurasian milfoil by using burlap at Lake Pémichangan can be viewed by clicking on the link below: