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Peconic River Ludwigia Control Project

invasive floating water primrose

DEC and partners have developed a plan to control Ludwigia peploides (floating water-primrose) in the Peconic River in Suffolk County. 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.

Ludwigia peploides fact sheet (PDF)

Herbicide Treatment

An herbicide treatment (a combination of imazamox and florpyrauxifen-benzyl) within the Peconic River is schedule to take place on June 1, 2021 in Brown's Bog adjacent to the DEC Edwards Avenue Boat Launch in Calverton (Suffolk County). This small treatment area (0.97 acres) will serve as a pilot study for controlling Ludwigia within the larger Peconic River.

Notification letters will be sent to riparian landowners of parcels adjacent to the Peconic River prior to treatment. Additionally, notification signage will be placed at all public access locations within the area impacted by treatment.


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 (floating water-primrose) is an aquatic plant that is invasive to New York State. 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. Primrose can impact recreation and tourism as well as the aquatic ecosystem it invades. It can also spread to other waterbodies via fragments on boats and fishing gear.

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 floating water-primrose (Ludwigia peploides). This project will be used to inform the five-year Ludwigia management plan that is being developed for the Peconic River. 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.

Proposed Plan for 2021

A small (< 1 acre) of Ludwigia peploides adjacent to DEC's Edward Avenue Canoe Launch will serve as a pilot control project for the herbicide treatment of invasive aquatic plants in the Peconic River. The results of the 2020 aquatic plant survey indicate that Ludwigia is found along the entire shoreline of Browns Bog. A single herbicide application is planned for early June 2021 using a combination of aquatic herbicides: ProcellaCOR-EC and Clearcast. A combination of these systemic herbicides will be applied to the leaves (foliar application) of Ludwigia peploides adjacent to the boat launch at a target concentration of 25 parts per billion (ppb). The herbicides will be absorbed by the plant tissue in the leaves and then will move to other parts of each Ludwigia plant. The in-water concentration in Peconic Lake is expected to be 1.0 ppb within twelve hours after treatment.

Pre- and post-treatment surveys are proposed for aquatic plants within and downstream of the treatment area. Comparison of the survey results will allow us to assess the effectiveness of the herbicide in reducing the Ludwigia infestation and to determine if native aquatic plants are being impacted (non-target impacts) by the herbicide. This data will inform future plans for treatment at Browns Bog and the other freshwater portions of the Peconic River. Funding for the 2021 pilot control project was provided by the US Fish and Wildlife Service (USFWS).


Permits are being prepared for the proposed 2021 pilot project including: a Notice of Intent for coverage under the State Pollution Discharge Elimination System (SPDES) General Permit 0-16-055, NYSDEC Article 15 Aquatic Pesticide Permits, and NYSDEC Article 24 Wetlands Permit. This page will be updated as permits are received.

Management Plan and Annual Reports

A Peconic River Ludwigia Control Project Five-Year Management Plan 2021-2025 is being prepared by NYSDEC and partners. This page will be updated as permits are received.

Resources and Herbicide Use

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 both herbicides. 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 here: Aquatic Life Benchmarks and Ecological Risk Assessment for Registered Pesticides (leaves DEC website).

Information about the herbicides:

Water Use Restrictions

The 2021 treatment will be conducted in early June and there will be no water use restrictions: swimming, boating, and fishing can continue as normal. However, please note that the herbicide labels identify a restricted use at concentrations above 1 part per billion (ppb) for 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 have retained SOLitude Lake Management (NYS applicator license #16506) to conduct the Ludwigia control project in 2021. SOLitude Lake Management will perform the herbicide treatment, aquatic plant surveys, and water sample collection.

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 annual 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