Giant Salvinia Identification & Treatment
Scientific Name: Salvinia molesta Category: Floating Tier: 2 — Regionally Significant — Common in multiple EPA ecoregions
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Identification
Giant salvinia is a free-floating fern with small, oval to oblong leaves (1/2 to 1-1/2 inches) arranged in pairs along a central stem. Young leaves lie flat on the water surface; mature leaves fold upward along the midrib, forming a chain-like pattern. The upper leaf surface has distinctive rows of tiny hair-like structures (trichomes) that are joined at the tips, forming an egg-beater or whisk shape. Key distinguishing features:
- Paired floating leaves with characteristic folding pattern
- "Egg-beater" shaped hairs on leaf surface (visible with hand lens)
- No true roots — has root-like modified leaves that dangle below
- Can form mats several feet thick in severe infestations
Commonly confused with: Common salvinia (S. minima — smaller, hair tips are not joined), mosquito fern/Azolla (much smaller, reddish)
Treatment
- Harvester (diquat) — Contact herbicide for knockdown.
- Propeller (flumioxazin) — Contact herbicide effective on floating plants.
Biological control: The salvinia weevil (Cyrtobagous salviniae) is an effective biocontrol agent in southern US waterways.
Regional Note: Giant salvinia is primarily a concern in USDA Zones 8–11. It is killed by frost but can persist year-round in protected or artificially warmed water bodies (e.g., power plant cooling reservoirs) further north.
Full Profile
- Native Range: Brazil
- US Distribution: Gulf Coast and Southeast — Texas, Louisiana, Mississippi, Alabama, Florida, Georgia, South Carolina. EPA Ecoregions: Western Gulf Coastal Plain, Southern Coastal Plain, Mississippi Alluvial Plain. USDA Zones 8–11.
- Regulatory Status: Federal Noxious Weed. Highly regulated in southern states.
- Habitat: Still or slow-moving freshwater. Ponds, lakes, bayous, reservoirs.
- Reproduction: Fragments. Does not produce viable spores. Even tiny fragments regrow rapidly.
- Ecological Benefits: Minimal. Dense mats cause severe oxygen depletion, block light, impede navigation, and devastate native aquatic ecosystems.
Sources: Texas A&M AquaPlant – Giant Salvinia | USDA APHIS
Related Species
- Duckweed (Lemna minor and related species (L. gibba, L. turionifera, Spirodela polyrhiza)) — Floating, Tier 1
- Watermeal (Wolffia spp. (W. columbiana, W. brasiliensis)) — Floating, Tier 1
- Water Hyacinth (Eichhornia crassipes) — Floating, Tier 1
- Water Lettuce (Pistia stratiotes) — Floating, Tier 2
- European Frog's-bit (Hydrocharis morsus-ranae) — Floating, Tier 3
- Mosquito Fern (Azolla) (Azolla spp.) — Floating, Tier 3
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