Eurasian watermilfoil hybrid
Myriophyllum spicatum x Myriophyllum sibiricum
Washington State Classification
Class C — Widespread, County-Selected Control
Eurasian watermilfoil hybrid is a new noxious weed for 2018.
Quick Reference
Identification
Growth Habit
Eurasian watermilfoil, northern watermilfoil, and Eurasian watermilfoil hybrids all look very similar. All three are submersed perennials with feather-like, submersed leaves. Their flowering stems have small flowers and very small leaf-like bracts that typically rise above the water's surface. Eurasian watermilfoil hybrids have intermediate characteristics, including a variable number of leaflets (also called segments), usually in a range of overlap between the parent species. Identification of the hybrid requires morphological and genetic analysis due to its intermediate characteristics.
Leaves
Eurasian watermilfoil hybrid has two types of leaves, feather-like, submersed leaves and very small leaf-like bracts on the flowering stem, which typically rise above the water's surface. Leaves with overlapping traits of parents, with submersed leaves having 16 to 28 leaf segments, and being 0.63 to 1.73 inches (16 to 44 mm) long. Click here to see an example.
Flowers
Many flowers are borne on an unbranched stalk to 6 inches long, usually rising above the water's surface. On the stalk, female flowers are at the bottom, and male flowers are at the top, with bisexual flowers in between. Flowers usually in whorls of 4. Flowers have 4 sepals and petals that are small, cream to purplish, often deciduous. Flowers are wind pollinated.
Fruit & Seeds
Rounded fruits with 4 lobes, divides into 4 mericarps (single seeded structures).
Impact
Eurasian watermilfoil hybrid is a new noxious weed for 2018. This perennial hybrid, a cross between the invasive Eurasian watermilfoil (Myriophyllum spicatum) and the native northern watermilfoil (Myriophyllum sibiricum), can result in a variety of strains--some that are aggressive and tolerant to some herbicide control treatments. Some genetic strains of this hybrid can be even more aggressive than Eurasian watermilfoil. For further information about identifying and controlling Eurasian watermilfoil hybrid, please contact Wesley Glisson with the Washington Department of Ecology.
Ecology & Spread
Habitat
Eurasian watermilfoil hybrid is documented in both eastern and western Washington. Click here to see a county-level distribution of Eurasian watermilfoil hybrids in Washington.
Spread Mechanisms
Reproduction
Eurasian watermilfoil hybrid, like its parents, can reproduce by seed and vegetative reproduction. Vegetative spread is generally considered the major method of reproduction within a waterbody, and is accomplished by three mechanisms: stolons (rhizomes), autofragments and allofragments. Autofragments (common with Eurasian watermilfoil and thought to variably occur with the hybrid) are typically created in late summer when short (15 to 20 cm) sections of the stem tips will develop roots and automatically separate from the parent plants. Allofragments are created by mechanical disturbance of plants such as from wave action or boat propellers. Those broken sections of stem will then form roots and settle to the bottom.
"
Control Methods
Mechanical
Cultural / Prevention
- Reduce weed infestation by handpulling weeds. Digging and carefully removing all rhizomes will effectively eliminate single plants and small infestations.