Download Eurasian watermilfoil

Eurasian watermilfoil
Myriophyllum spicatum
Watermilfoil family
Key identifying traits
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Under water foliage usually found in whorls of 4
around the stem; no above surface leaves
Each mature leaf has 12 or more pairs of leaflets;
native milfoil has less than 12
Leaves appear feather-like or like fine herring
bones and tend to collapse around stem if
removed from the water unlike courser native
milfoil that retains it’s shape out of water
Small flowers are borne on leafless, reddish
spikes that stand a few inches above the water
and submerge after pollination
Rooted plants will grow in water as deep as 25-30
feet depending on water clarity
flowering stem
Biology and ecology
 A perennial plant that does produce seeds but
that spreads almost entirely from fragments;
plants naturally fragment in late summer & fall
 Fragments are also caused by and transported
from place to place by watercraft and trailers
 Dense mats can form making boating, fishing and
swimming impossible and displacing native plants
 Once commonly sold as an aquarium plant but now
one of the most problematic plants in Washington
Milfoil “whorl”
Control
Prevention – Learn to identify plants; know your
Eurasian milfoil on left; coarser, Northern
waterbodies; beware of and check for plant
(native) milfoil on right
fragments transported on watercraft and trailers
Biological – Sterile grass carp or milfoil weevil may
have very specific and limited application
Cultural – Healthy native plant communities help
reduce likelihood of establishment but don’t stop it
Mechanical – Harvesting, rotovation, pulling, dredging
and bottom barriers all have their uses
Chemical – Some effective at label rates but can only
be used with required permits and licenses
Dangerous mats formed by Eurasian milfoil
Where found – Found in several Stevens County lakes and rivers and in many nearby counties
as well. Statewide spread has been dramatic since first found near Seattle in 1965.
Created by Stevens County Noxious Weed Control Board, March 2001; Updated Jan 2004