At its February board meeting, the Adirondack Park Agency heard a report presented by Aaron Ziemann, a project analyst with the agency, on the effectiveness of treatment efforts against Eurasian Watermilfoil — an invasive aquatic vegetation that has become widespread throughout the Adirondack Park and has proved difficult to control by natural methods, such as hand-harvesting or matting.

In response to the rapid spread, the APA approved the use of ProcellaCOR, an herbicide, to treat Eurasian watermilfoil in several Adirondack lakes last summer — with many of the permit applications coming in the wake of a state appellate court decision that handed the APA the ability to consider and grant the approval of the herbicide.

Ziemann’s presentation examined the post-treatment results from each lake, focusing on the herbicide’s effectiveness against milfoil, its effects on non-target vegetation, its breakdown and rate of decrease in concentration after application.

Ziemann noted that while there was success in treatment application sites, the reduction in Eurasian watermilfoil was also seen park-wide since 2021, including on water bodies where treatment was not undertaken. He suggested a variety of natural environmental patterns, and added that the data did not support the reductions occurring as a result of hand-harvesting alone.

“Fluctuations could be due to natural year-to-year changes influenced by environmental factors such as water temperature, nutrient levels or other ecological dynamics that affect milfoil growth cycles,” he said. “Across the park, we and other observers have noticed a marked decrease in Eurasian watermilfoil growth. The broader pattern suggests some regional factor may be influencing those declines but pinpointing the exact causes remains challenging.”

What is ProcellaCOR?

ProcellaCOR is a relatively new herbicide. It was first developed in 2010 by the sePRO Corporation, a large aquatic herbicide development and manufacturing company. The herbicide’s active ingredient is florpyrauxifen-benzyl, which mimics the plant’s growth hormone, disrupting it and ultimately killing it.

The herbicide was engineered to selectively-target Eurasian watermilfoil and a number of other invasive species, while not impacting native vegetation in the Adirondacks. In his presentation, Ziemann said post-treatment studies showed that native vegetation was minimally impacted by ProcellaCOR, and that the impacts were generally what was expected by the agency when it granted the permits.

The herbicide has not been shown to adversely impact human or animal health in scientific studies to date. It was approved for use by the United States Environmental Protection Agency in 2017, along with the New York state Department of Environmental Conservation, European Union and Canadian health agencies in 2019, 2018 and 2023, respectively.

Proponents of ProcellaCOR point to its precision. The Lake George Park Commission — which led the effort to use the herbicide in selected locations on Lake George, ultimately prevailing over objections from the Lake George Association and a number of area residents — stated that the herbicide is effective at much lower rates of application than previous herbicides.     

“It is applied at a dosage of approximately 7 parts per billion, which is 1,000 times less dosage than the aquatic herbicide previously approved by the Adirondack Park Agency,” the document states. “Following application, there are no restrictions on potable water usage (drinking water) or on contact recreation such as swimming.”

Opponents of its use contend that while no adverse impacts have been shown yet, its relatively-new status as a widely-used herbicide have not allowed enough time to fully understand its potentially-adverse effects.

Responses from various organizations and entities opposed to its use cite past pesticides and herbicides that initially appeared to be safe and effective, before adverse impacts were sometimes found years after its initial application. There are also concerns that the herbicide could impact non-target native vegetation and water quality in more detrimental ways than current studies point to.

Legal battles

ProcellaCOR faced opposition when it was originally floated as a treatment solution to Eurasian watermilfoil, with various lake associations, local officials and residents voicing concerns that the herbicide could pose unintended environmental and health risks. Soon, the matter was before the courts.

The Lake George Association sued the APA in 2022 after the agency granted use of the herbicide by the Lake George Park Commission, claiming that the agency did not follow appropriate regulatory steps in not holding a public hearing.

A Warren County state Supreme Court justice agreed, finding the action to be arbitrary and capricious in the court’s ruling issued on March 3, 2023. The APA appealed the decision to the state Appellate Division’s Third Judicial Department where a panel of justices unanimously overturned the lower court’s decision on May 2, 2024.

In its decision, the appeals court wrote that the APA had complied with its regulatory obligations. The court cited the APA’s public meeting on April 14, 2022, which was within 60 days of the herbicide permit being deemed complete.

“Therefore, Supreme Court should have dismissed the petition in its entirety, and we make the appropriate entry,” the court’s opinion stated.

Following the appellate court’s decision, a number of other entities overseeing certain lakes in the Adirondacks moved to file permit applications for use of the herbicide, with the APA granting permits for seven other lakes, in addition to Lake George, where the Lake George Park Commission had re-applied for the permit after the appeals court decision.

Treatment results

The applications began in 2024 in select locations where Eurasian watermilfoil was growing across the Adirondacks: Paradox Lake, Brant Lake, Horseshoe Pond, East Caroga Lake, West Caroga Lake, Highland Forge Lake, the Chateaugay Narrows and Lake George — where the applications focused on Blair’s Bay and Sheep Meadow Bay.

The permits for those water bodies were filed, respectively, by the Paradox Lake Association, Brant Lake Foundation, Deer River Flow Association, the town of Caroga — for both East and West Caroga lakes — Highland Forests LLC and the Lake George Park Commission — for both bays in the lake.

The permit grants had a number of stipulations, including specific application locations, concentration limits and post-treatment monitoring to be presented to the APA.

Ziemann’s presentation showed that in all of the treatment areas, there were drastic reductions in Eurasian Watermilfoil, with the plant’s frequency falling to either zero or single digits as a percentage within the studied sites. Prior to treatment, their frequency ranged from 25% to 78% in the various lakes, according to Ziemann’s presentation.

Ziemann played video footage from divers that showed sizeable dead zones where Eurasian watermilfoil had previously been growing out of control. He said that there is a general sufficient richness of native species surrounding where the Eurasian watermilfoil had been wiped out to begin filling in those areas.

He said all of the data pointed to the herbicide breaking down in the manner that it was anticipated, with post-treatment water sampling showing that the herbicide’s concentration levels had fallen after treatment as expected.

Ziemann noted in his conclusion that professional application remains necessary in future uses to ensure the herbicide is applied in a manner that takes weather and lake conditions into effect. He said data from 2024 showed that applicators were successful in keeping the herbicide to the intended areas, and were cognizant how lake dynamics and currents often have to be factored in to achieve such results.

What is Eurasian

watermilfoil?

As its name suggests, the plant is native to portions of Europe, Asia and northern Africa. It was introduced to North America in the 1940s, and is now found in 48 states and three Canadian provinces, according to the Paul Smith’s College’s Adirondack Watershed Institute.

The plant, while not known to be toxic to humans, grows very rapidly — as much as 2 inches per day, according to the Adirondack Watershed Institute — in Adirondack water bodies, and begins doing so earlier than native plants each spring. The plant also spreads easily between water bodies as small fragments of it hitch a ride on watercraft, often unbeknownst to boaters in the absence of a careful washing and inspection.

This rapid growth and spread often turfs out native vegetation, wreaking havoc on the broader natural ecosystem. The Adirondack Watershed Institute notes that the plant makes for poor fish spawning areas, and can dent their populations as it becomes more widespread.

Additionally, the dense nature of Eurasian Watermilfoil impacts human recreation by rendering swaths of previously-open water that could be used for swimming or boating inaccessible as the weed clogs up the water.

Various watershed associations throughout the park have tried a variety of ways of combatting Eurasian watermilfoil’s spread, including hand-harvesting. As it became more widespread and uncontrollable the management conversation increasingly turned to ProcellaCOR.