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Eurasian watermilfoil

Eurasian watermilfoil

Eurasian watermilfoil

(Myriophyllum spicatum )

Priority: -  Control

Tags: Aquatic | Biocontrol

Identification and Reproduction

Identification: 

  • Eurasian watermilfoil is an herbaceous, perennial, aquatic plant.
  • It has thin stems, which can be green, pinkish-white, or reddish-brown and can grow 1-10 metres long.
  • The leaves are feathery and green, and form four-leaf whorls around the stem. On each leaflet/rachis there are at least 12 individual segments. 
  • Leaves stay submerged underwater as they are very flimsy. 

  • Flowers are small and red, protruding from the water. 
  • This plant also produces round seed capsules. 

Reproduction: 

  • Primarily vegetatively thorugh stolons or lateral roots. 
  • This plant reproduces by seeds, which can remain dormant for long periods. 
  • It will overwinter as root crowns and reshoot in the spring, surviving winter conditions. 

Habitat & Ecology

  • This plant prefers shallow, slow-moving water, ranging from 1-3 m deep, but it has the potential to root to a dept of 10 m. 
  • It prefers alkaline water, and will grow well in disturbed areas where previous vegetation has been removed.

Impacts

Social: 

  • It will block drainage canals, irrigation ditches, and other waterways.
  • It also impedes swimming, fishing, and boating activities. 

Ecological: 

  • This invader forms dense vegetative mats and can grow across entire lakes.
  • It crowds and shades out native plants, reducing biodiversity and disrupting natural habitats of fish and wildlife.
  • Dense mats also block the flow of water and creates a great habitat for mosquito larvae.
  • As the plant decomposes, it robs the water of oxygen, and changes water temperature and pH.

Management

Prevention is a high priority for this plant. Always clean, drain, and dry aquatic equipment like boats or canoes before transferring from one body of water to another. Never grow or intentionally transport this plant, or dispose of aquarium plants in waterways or down the drain.

Biological Control:

Currently a two of native insects can help manage Eurasian watermilfoil: Eurychiopsis lecontei and Cricotopus myriophylli. They both feed on the stems of the plant, reducing growth rates. 

Resources

Download the Invasive Species Council of BC's Factsheet for Eurasian Watermilfoil here.

Header photo (Donald Hobern).