Delta Ponds Ludwigia Control

Delta Ponds Ludwigia composite
Before & after pictures of Delta Ponds overrun with invasive Ludwigia

WHAT IS IT? Ludwigia hexapetala or Uruguayan primrose willow is an invasive aquatic plant originally from South America. It is possible that this plant was introduced to this area when someone dumped the contents of a fresh-water aquarium into the ponds which contained a young live aquarium plant.

  • It doubles its biomass in 15 to 20 days, forming dense mats both above and below the waterline which then chokes out entire waterways.
  • Western pond turtles, fish, ducks, and other wildlife cannot swim through infested areas, limiting available habitat.
  • In addition to spreading by seed, it reproduces from plant fragments that break off and migrate downstream, infesting new waterways.
  • Dense mats of Ludwigia block sunlight from the water’s depths, killing off native aquatic plant species essential to sustain local wildlife.
  • Large mats die back in early winter, depleting the oxygen levels in the water.
  • Without adequate oxygen, juvenile Chinook salmon that use the Delta Ponds as over-wintering habitat will be impacted and may even die.

  • This infestation is the most upstream population on the Willamette River and has the potential to spread downstream and invade the Willamette watershed. 
  • The invasive nature of this plant has the potential to undo all of the recent environmental and economic efforts to improve habitat at Delta Ponds for juvenile Chinook salmon and Western pond turtles.

WHAT ARE WE DOING TO MITIGATE THE CONCERN? In July 2014, we began controlling ongoing growth of this invasive species by utilizing a combination of manual pulling and careful spraying of an aquatic-approved herbicide.

WHO DO I CONTACT FOR MORE INFORMATION? For more detailed information, please contact Lauri Holts, Natural Resources Enhancement Coordinator for the City of Eugene at 541-682-4925.

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