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Ludwigia peploides

Biological Category 
Species Type 
Aquatic Invasives
NY Invasiveness Rank 
Very High
LHPrism Status 
Tier 1 - Threat

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A member of the primrose family (Onagraceae), Floating primrose willow is a floating aquatic perennial. Early growth is a rosette of leaves. These plants are most conspicuous in bloom, when bright, five petaled flowers emerge on stems held above the water. 

Leaves are alternately arranged, appearing whorled from above, oval to lance-shaped, shiny, glabrous and up to four inches in length. (3)

Flowers are five petaled, bright yellow primrose-type flowers an inch in diameter and are often held on long stalks above the water. (3) 

Introduction History 
Floating primrose willow is native to Central and South America, and parts of the southern United States. Introduction to the Northeast likely occurred in the 1800s, when the plant was widely used as an ornamental. The species is now extant in at least 30 states. (2)
Ecology and Habitat 
Floating primrose willow establishes in a variety of substrates in shallow, slow-moving waters such as at the edges of ponds, lakes, rivers and streams, and in man-made environments, such as ditches. (5)
Reproduction and Phenology 
Floating primrose willow reproduces both vegetatively, via stem fragments, and sexually, via prodigious production of seed. Stem fragments are buoyant and easily dispersed by water or, potentially even longer distances by waterfowl. (5) Vectors include water, human activity and waterfowl. (6)
Impacts of this species 

Floating primrose willow is an aggressive invader of the freshwater shorelines of lakes, ponds and streams, although it will colonize any slow-moving body water.  Capable of traveling great distances via waterfowl, this species can establish new colonies from both stem fragments and seeds. Dense aggregations can shade out plants growing below it, thereby altering the diversity of the communities it invades. Furthermore, this species is allelopathic, inhibiting the germination of vulnerable plants. The thick vegetative mats formed by large infestations can cause anoxic conditions, particularly in the summer, reduce water flow and stabilize sediments, and increase sulphide and phosphate levels causing a cascade of ecological changes. (1)

Management Methods 

Biological Control
The flea beetle, Lysathia flavipes, reportedly causes heavy damage to Floating willow primrose, although it is not target specific. (8)

Manual or Mechanical Control
Pulling / Digging Up: Not advisable. Although mechanized mass pulling on very large populations in conjunction with herbicide usage can help reduce seed rain. (7)

Mowing: Not advisable. Mowing or cutting can leave easily dispersible fragments than can establish new populations elsewhere. (7)

Girdling: Not applicable

Prescribed Fire: No information available

Prescribed Grazing: Not applicable

Soil Tilling: Not applicable

Mulching: Not applicable

Solarization: Not applicable

Hot Foam Spray: Not applicable

Chemical Control
The pesticide application rates and usage herein are recommendations based on research and interviews with land managers.  When considering the use of pesticides, it is your responsibility to fully understand the laws, regulations and best practices required to apply pesticides in a responsible manner.  At times, the pest you seek to treat may not be on a pesticide label, requiring a 2ee exemption from NYSDEC.  Always thoroughly read the label of any pesticide and consult the NYSDEC or a licensed pesticide applicator with questions.

Foliar Spray: There are a number of herbicides available for use on Floating primrose willow A wetland safe 1-2% solution of Triclopyr or glyphosate is effective at managing populations of Marsh dewflower. Treatment should be performed prior to fruiting/seed set. 2 4-D is also suitable for use, as is Imazapyr and Imazamox. Follow up treatment may be necessary in subsequent years.  (7)

Cut Stump: Not applicable

Basal Bark: Not applicable

Stem Injection: Not applicable

Pre-Emergent Spray: Not applicable

Summary of Best Managment Practices 

General management overview and recommendation
As with any other invasive infestation, large occurrences of Floating primrose willow are best managed via a combination of mechanical and chemical means.  Small populations can be hand pulled but care must be taken to remove all plant material. Dense patches must be sprayed to attain good control. All managed infestations should be monitored to prevent reinvasion from nearby populations, or re-sprouting of vestige fragments. Any new occurrences can be sprayed. 

Post treatment monitoring
Any infestations managed by chemical means must be revisited in 2-3 weeks to check for treatment efficacy. Follow up spot treatments may be necessary for at least one year after initial treatment. 

Disposal Methods
Any pulled for fragmented plant material must be bagged and disposed of in a landfill or thoroughly dried and composted.