Purple Loosestrife Identification & Treatment
Scientific Name: Lythrum salicaria Category: Emergent Tier: 3 — Localized — Limited geographic range or lower frequency
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Identification
Purple loosestrife is a tall (3–7 feet) perennial with showy purple-magenta flower spikes and opposite or whorled lance-shaped leaves. Stems are square or slightly angled. Forms dense stands along shorelines, wetlands, and wet meadows. Key distinguishing features:
- Tall spikes of bright purple-magenta flowers
- Square or angled stems
- Opposite or whorled lance-shaped leaves
- Dense shoreline stands
Treatment
- Glyphosate 5.4 — Applied to actively growing foliage. Spot treatment preferred near water.
Biological control: Highly successful. Three host-specific insects (Galerucella calmariensis, G. pusilla, and Hylobius transversovittatus) have been released across the US and have significantly reduced purple loosestrife populations in many areas.
Full Profile
- Native Range: Europe and Asia
- US Distribution: Northern and central US — all northern tier states. EPA Ecoregions: Northern Lakes and Forests, North Central Hardwood Forests, Northeastern Highlands, Willamette Valley. USDA Zones 3–8.
- Regulatory Status: Listed as noxious or invasive in most states where it occurs. Federal Noxious Weed.
- Habitat: Wetlands, pond/lake margins, river floodplains, ditches. Prefers full sun and wet to moist soil.
- Reproduction: Seed (a single plant can produce 2.5 million seeds per year) and vegetative regrowth from roots.
- Ecological Benefits: Provides nectar for bees and butterflies but overwhelmingly negative ecological impact — displaces native wetland plants (cattails, bulrushes, sedges), reduces wildlife habitat value, and degrades wetland function.
Sources: MSU Extension | USDA PLANTS Database | USDA APHIS
Related Species
- Cattails (Typha latifolia (broadleaf), T. angustifolia (narrowleaf), T. × glauca (hybrid)) — Emergent, Tier 1
- Phragmites (Common Reed) (Phragmites australis subsp. australis (invasive) vs. P. australis subsp. americanus (native)) — Emergent, Tier 1
- Creeping Water Primrose (Ludwigia spp. (L. peploides, L. grandiflora, L. repens)) — Emergent, Tier 1
- Dollar Weed (Pennywort) (Hydrocotyle spp. (H. umbellata, H. ranunculoides, H. verticillata)) — Emergent, Tier 2
- Alligator Weed (Alternanthera philoxeroides) — Emergent, Tier 2
- Flowering Rush (Butomus umbellatus) — Emergent, Tier 3
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