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Peconic River Ludwigia Control Project

DEC will host two virtual public meetings to provide updates on the first full-scale season of the Peconic River Ludwigia Control Project.

Tuesday, December 13, 2022: 7:00 PM

Wednesday, December 14, 2022: 12:00 PM

DEC and partners have developed a plan to control an infestation of Ludwigia peploides within the freshwater portion of the Peconic River in Suffolk County. This invasive aquatic plant is known by various common names, including floating water-primrose or floating primrose-willow. Ludwigia peploides grows and spreads rapidly. Infestations can have negative impacts on recreation and tourism as well as severe consequences for the health of aquatic ecosystems and all the plants and animals that live there. It can also spread to other waterbodies via fragments on boats and fishing gear.

Ludwigia peploides fact sheet (PDF)


yellow water primrose flower
Water primrose flowers are bright yellow
and bloom in late spring
(Photo by Graves Lovell, Alabama Department
of Conservation and Natural Resources,

Ludwigia peploides is an aquatic plant that is invasive to New York State. Within New York, it was first discovered in the Peconic River (Towns of Brookhaven and Riverhead, Suffolk County) around 2003. Since that time it has grown and spread throughout the freshwater part of the river.

Despite more than a decade of hand removal efforts involving more than 5,000 hours of DEC staff and volunteer time, the infestation continues to grow and reduce access to recreation and angling on the river. For this reason, DEC is collaborating with national aquatic invasive species experts, Suffolk County Conservation Advisory Council (CAC), State University of New York at Stony Brook, and US Fish and Wildlife Service to conduct a pilot study of treatment methods for Ludwigia peploides as well as create a 5-Year Management Plan for the infestation. The plan will focus on adaptive management (evaluating the data from each year and making changes to plans for the coming year based on that data), define partnerships and goals, and demonstrate DEC's commitment to the project.

Five Year Management Plan

A Peconic River Ludwigia peploides Control Project, Five-Year Management Plan has been prepared by DEC and partners. In 2021, a systemic herbicide treatment (a combination of imazamox and florpyrauxifen-benzyl) was piloted in a small treatment area within the Peconic River and is proposed for use throughout the river between 2022-2024.

See the Peconic Ludwigia peploides Control Project Five-Year Management Plan (PDF).

Stakeholder Meetings

There are no upcoming stakeholder meetings scheduled at this time. The most recent stakeholder meetings were held virtually on Wednesday, February 16th and Thursday, February 17th, 2022.

2021 Pilot Treatment Project

A small (< 1 acre) of Ludwigia peploides adjacent to DEC's Edward Avenue Canoe Launch served as a pilot control project for the herbicide treatment of invasive aquatic plants in the Peconic River.

See maps showing Ludwigia peploides distribution post-treatment in September 2021 (PDF).

ludwigia - plant with green leaves and yellow flowers growing on water
Ludwigia plants before herbicide treatment
shriveled and dying ludwigia plants after treatment
Ludwigia plants after herbicide treatment

Aquatic plant surveys were completed prior to treatment and all Ludwigia peploides growing within the entire freshwater Peconic River was mapped. Pre-treatment site photos were taken the day of treatment. On August 26, 2021, the systemic herbicides ProcellaCOR EC and Clearcast were foliar applied in combination with a spray adjuvant to the Ludwigia peploides plants within the treatment area at a target concentration of 25 parts per billion (ppb).

All aquatic plants (both native and non-native) were surveyed for abundance within the treatment area three weeks after treatment. Area site photos were taken to document impacts at one week, three weeks, and eight weeks after treatment. Impacts to Ludwigia leaves and stems were obvious one week after treatment. Ludwigia abundance was reduced 50% by three weeks after treatment, and little to no Ludwigia survived 8 weeks after treatment. The floating aquatic invasive plant European frogbit (Hydrocharis morsus-ranae) was also successfully controlled within the treatment area as a result of the herbicide treatment. Impacts to floating foliage within the treatment area were observed in two of the eight native species (spadderdock and watershield). However, no impacts to aquatic plant species were observed outside of the treatment area. This finding demonstrates the importance of using a spray adjuvant and keeping foliar application within delinated treatment areas wherever possible and limiting application to direct spot treatments where Ludwigia occurs in trace and sparse abundance. Both spadderdock and watershield are common outside of the mapped Ludwigia polygons and it is anticipated that these native species would be able to recolonize the available habitat once Ludwigia is controlled.

DEC also surveyed benthic macroinvertebrates at multiple sites within the freshwater Peconic River pre- and post-treatment, and no changes to community assembly were observed.

Funding for the 2021 pilot control project was provided by the US Fish and Wildlife Service (USFWS). Data from this pilot project has informed the adaptive management strategy in the 5-Year Management Plan proposed for the other freshwater portions of the Peconic River.

2022-2025 Herbicide Treatment

All permits have been received for 2022 treatment season. As per the Article 15 Aquatic Pesticide Permit requirements, two rounds of riparian landowner notification letters were mailed and shoreline signage notifying of treatment will be posted at all public access points prior treatment.

The 2022 herbicide treatment will take place on July 27th, 2022. The treatment is a single herbicide application.

The following permits were obtained in order to conduct the 2022 treatment:

  • Notice of Intent for coverage under the State Pollution Discharge Elimination System (SPDES) General Permit 0-16-055, Permit ID NYP160548, (pending)
  • NYS Environmental Quality Review Act (SEQR) Negative Declaration posted in ENB January 12, 2022,
  • NYSDEC Article 24 Freshwater Wetlands Permit - ID 1-4722-02195/00014,
  • NYSDEC Article 15 Aquatic Pesticide Permit for ProcellaCOR EC,
  • NYSDEC Article 15 Aquatic Pesticide Permit for Clearcast,
  • NYSDEC Article 15 Title 27 Wild, Scenic & Recreational Rivers Permit - ID 14722-02195/00015, and
  • FIFRA 2(ee) - ID 579281

Funding for the 2022-2025 project was provided by the Environmental Protection Fund.

Water Sample Results

Surface water samples will be collected throughout the Peconic River as per the Article 15 Aquatic Pesticide Permit requirements. Surface water will be analyzed for both active ingredients: florpyrauxifen-benzyl (ProcellaCOR EC) and imazamox (Clearcast) to a 1.0 pbb detection limit. This webpage will be updated as water samples results are received. Lab reports will be linked here. Samples will be collected until all sites are non-detect.

Clearcast - Day of Treatment Results (PDF)
Clearcast - 24 hours after Treatment Results (PDF)
Clearcast - 1 week after Treatment Results (PDF)
Cleracast - Treatment Results from 08/29/22 (PDF)

ProcellaCOR EC - Day of Treatment Results (PDF)
ProcellaCOR EC - 24 hours after Treatment Results (PDF)
ProcellaCOR EC - 1 week after Treatment Results (PDF)

Resources and Herbicide Use

invasive floating water primrose

No adverse impacts of Clearcast (imazamox) and ProcellaCOR (florpyrauxifen-benzyl) on human health have been documented by USEPA (Human Health Benchmarks for Pesticides) (leaves DEC website). No impacts on fish and invertebrates occur at label rates of either herbicide. Native plants could be minimally impacted by the herbicides which is why we are surveying plants both pre- and post-treatment. Additional information can be found on the EPA's webpage about Aquatic Life Benchmarks and Ecological Risk Assessment for Registered Pesticides (leaves DEC website).

Information about the herbicides:

Water Use Restrictions

The 2022 treatment is scheduled for July 2022 and there are no water use restrictions: swimming, boating, and fishing continued as normal. However, please note that the herbicide labels identify a restricted use at concentrations above 1 part per billion (ppb) for irrigation of greenhouse plants. Please see the table below for detailed information regarding water restrictions.

Product Name Swimming Fishing Livestock Watering Drinking Irrigation
ProcellaCOR EC No Restrictions No Restrictions ≥1 ppb do not use for livestock watering No Restrictions

≥1 ppb do not irrigate agricultural crop, greenhouse nursery, or hydroponic plants*

(*unless an activated carbon or similar filtration process is utilized prior to water use)

Clearcast No Restrictions No Restrictions No Restrictions No Restrictions

≥1 ppb do not irrigate greenhouse or nursery plants*

(*unless an activated carbon or similar filtration process is utilized prior to water use)


DEC and State University of New York at Stony Brook retained SOLitude Lake Management (NYS applicator license #16506) to conduct the Ludwigia control project in 2021. SOLitude Lake Management performed the herbicide treatment and aquatic plant surveys and mapping. DEC retained Adirondack Research to conduct the pre- and post-treatment aquatic plant surveys for 2022-2024 as well as additional aquatic plant surveys in 2025-2026. DEC retained the Pond and Lake Connection (NYS applicator license # ) to conduct the herbicide treatments and water quality monitoring in 2022-2024.

Citizen Science

Visitors to the Edwards Avenue Boat Launch in Calverton are encouraged to take photos of the pilot project site and submit them to Chronolog. A device mounted near the launch will allow visitors to take a series of time lapse photos that we will us to track the impacts of the treatment on the Ludwigia in Browns Bog. For more information about the Chronolog project, visit its website (leaves DEC website).

Future Work

Ludwigia peploides is notoriously difficult to manage because it reproduces in several ways. Control projects can take several years of treatment before they are considered successful. Detailed reports and updated information will be made available on this webpage. Please check back regularly for updates.

Contact Information

Please contact us if you have any questions or need additional information.

Local Contact:

Heidi O'Riordan, Fisheries Manager, NYS DEC, Region 1
50 Circle Road
Stony Brook, NY 11790-3409, 631-444-0280

Bureau of Invasive Species and Ecosystem Health:

Cathy McGlynn, Aquatic Invasive Species Coordinator, NYS DEC,
625 Broadway, 5th Floor
Albany, NY 12233-4253, 518-402-9425