Eurasian Watermilfoil

Myriophyllum spicatum L.
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Status:
County Declared
•
Priority 1
Synonyms:
Spiked watermilfoil, spike watermilfoil Myriophyllum spicatum var. muricatum

Description

Eurasian watermilfoil is a perennial, primarily submerged, mat forming aquatic plant in the Haloragaceae (watermilfoil) family. Leaves are finely dissected with 12 to 21 leaflet pairs giving the plant a feathery appearance. Leaflets are ½ to 2 inches long. Leaves are arranged in whorls of 3 - 6 leaves on stems. Leaves are grayish-green, and stems may be white, pink, brown, or reddish-brown. Stems may be 3 to 12 feet long and are branched near the water surface. Stems are easily fragmented. Eurasian watermilfoil has both male and female flowers. Flowers are very small and may be pink, yellow, or red. Flowers occur in small spikes that emerge 2 to 4 inches above the water surface. Male flowers have four petals; female flowers lack both petals and sepals. Eurasian watermilfoil produces seeds in segmented capsules each containing four seeds. Roots are an extensive network of rhizomes.

Origin and Spread

Eurasian watermilfoil is native to Europe, Asia, and North Africa and was likely accidentally introduced to North America in the late-1800s or early-1900s. It spreads locally by rhizomes, stem fragments, and seeds, and it is spread to other bodies of water as vegetative material attached to watercraft and equipment. Wyoming is the only state where Eurasian watermilfoil has not been found.

Management Options

Prevention strategies should be utilized as much as possible. Clean Drain Dry watercraft and trailers after leaving a body of water.

Cultural control strategies include maintaining a healthy nutrient balance by reducing runoff from lawns and pastures, but these strategies are not always viable in natural systems.

There are not any biological controls currently available for Eurasian watermilfoil.

Raking, cutting, or pulling by hand can reduce small stands of Eurasian watermilfoil, but all fragments must be removed to prevent reestablishment.

Dense infestations can be managed with herbicides. Because of the complexity of using herbicides in aquatic systems, TCWP recommends that you contact our office or Wyoming Game and Fish before conducting aquatic treatments.

Additional Resources