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Eurasian Milfoil

• • Yellow Buoys

From 2007 to 2009, an increased volume of plants was reported in Lac Mahon, apparently including Eurasian milfoil. Increased phosphate use was identified as a likely cause. Harvesting was considered the best control, with collection and disposal away from the lake. The Association considered buying a manual cutter but didn't due to liability issues. Fortunately, aquatic plants (milfoil or otherwise) receded after that.

In 2017, concerns about the presence and spread of Eurasian milfoil in Lac Mahon led to a September field study done by ABV des 7 to inventory aquatic plant beds in the lake. According to the study (attached in French, along with a summary in English),

• • Milfoil is present in many places and densities, including two small plant beds that were more than 80% milfoil.

  • Milfoil could spread quite quickly if preventive measures are not applied.

  • The plant spreads mainly by fragmentation, so it is important to prevent boat traffic in infested areas, which can be done with warning buoys and signs.

  • Burlap can be used to control milfoil, requiring government approval.

Eurasian milfoil had spread by 2018 (see Eurasian Milfoil Locations, including  photos of Eurasian milfoil beds), leading to the use of Yellow warning buoys.

Eurasian milfoil and other invasive species spread primarily as hitch-hikers on boats, trailers and equipment, so boat-cleaning is a key preventative, see the Boat-washing checklist and Boat pressure-washing (in News).

Other Prevention and Control

ABV des 7 has worked with other lake associations to assess and mitigate Eurasian milfoil, e.g. at Lac Bernard and Lac Blue Sea. In 2017, the municipalities of Blue Sea and Messines made boat pressure-washing mandatory.

Under current (revised) Quebec regulations, manual installation of benthic mats up to 75 square metres per lake does not require authorization. Burlap (jute) tarps decompose, other types of mats can be reused but are more expensive.  See DIY Burlap Dock Kit, Lake Bottom Blanket.

Individual milfoil plants can be pulled out and disposed by hand, with best efforts to get all of the root, avoid fragmentation, and collect any pieces that do break off.

According to the Okanagan Basin Water Board, the limiting nutrient for Eurasian milfoil is nitrogen, not phosphorus (which is a limiting factor in the production of algae). One study found a significant response of Eurasian milfoil to nitrogen enrichment, and no response to phosphorus enrichment. See Water Quality.

Identification

Here are some key identifiers to help recognize Eurasian milfoil:

• • grows in shallow water (up to 3 metres deep)

  • long, stringy stems branch near the water surface into many stems

  • forms dense mats

  • red buds at the tips of the plant

  • feathery leaves

  • small reddish flowers above water (mid-summer)

See attachments

• Eurasian milfoil Watch Card, Sudbury 

• Myriophyllum spicatum, Eurasian milfoil ABV-7, and Myriophylle-epi for photos (individual and massed).

To help distinguish Eurasian milfoil from native species such as Northern milfoil and Coontail, see Look-alike card and Look-a-likes, 

Other Invasive Species

See attachments and Invasive Species in Links for information on other invasive species. Preventing their introduction is a priority.