Northern Watermilfoil Identification & Treatment
Scientific Name: Myriophyllum sibiricum Category: Submerged Tier: 3 — Localized — Native species, lower management priority
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Identification
Northern watermilfoil has feather-like leaves arranged in whorls of 4 around the stem, similar to Eurasian watermilfoil. However, it has fewer leaflet pairs per leaf (typically 5–12 vs. 12–21 for Eurasian) and a less dense overall growth habit. Stems are lighter green and less branched. Leaves tend to be stiffer and more robust when removed from water. Key distinguishing features:
- Feather-like leaves in whorls of 4
- Fewer leaflet pairs (5–12) than Eurasian watermilfoil
- Less dense, less branched growth habit
- Stiffer leaves out of water
Commonly confused with: Eurasian Watermilfoil (more leaflet pairs, denser growth, limp out of water). Hybrids between Northern and Eurasian watermilfoil are increasingly common and can be difficult to distinguish visually — genetic testing may be required.
Treatment
Northern watermilfoil is a native species and generally does not require aggressive management. Selective treatment is recommended only when growth interferes with pond use.
- Aquathol K (endothall) — Contact herbicide for localized knockdowns.
- Navigate or Sculpin (2,4-D) — Selective systemic herbicide.
Important: Confirm identification before treating. If Eurasian watermilfoil is suspected, use systemic treatment. Hybrids may require more aggressive management.
Full Profile
- Native Range: North America
- US Distribution: Northern tier states, especially Great Lakes region. USDA Zones 3–7.
- Regulatory Status: Not regulated (native).
- Habitat: Lakes, ponds, and slow-moving streams. Prefers cooler water than Eurasian watermilfoil.
- Reproduction: Spreads by fragmentation and seed. Less aggressive than Eurasian watermilfoil.
- Ecological Benefits: Provides habitat for fish and invertebrates. Supports native aquatic ecosystems. Should be preserved where possible unless severely overgrown.
Sources: Texas A&M AquaPlant | USDA PLANTS Database
Related Species
- Eurasian Watermilfoil (Myriophyllum spicatum) — Submerged, Tier 1
- Parrot Feather (Myriophyllum aquaticum) — Emergent, Tier 2
- Coontail (Hornwort) (Ceratophyllum demersum) — Submerged, Tier 1
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