Battling the Hydra: Treatment of Hydrilla in Cayuga Lake

In Greek myth, the Hydra is a creature capable of great power. For every head that is removed - two more replace it - making the Hydra a difficult foe to defeat. This resiliency of the Hydra, and its ability to withstand repeated damage, inspired the name of an aquatic plant that shares many characteristics with the monster of legend. Native to the cool waters of Eastern Asia, Hydrilla (Hydrilla verticillata) has been subject to an ongoing eradication campaign in Cayuga Lake for the past decade.

Leading the charge against the Hydrilla infestation, the Hydrilla Task Force unites partners from throughout the region. These partners include:

• Bolton Point Water System
• Cayuga County Department of Health
• Cayuga Lake Watershed Network
• Cooperative Extension of Tompkins County
• Finger Lakes Institute at Hobart and William Smith Colleges
• Finger Lakes/Lake Ontario Watershed Protection Alliance
• Finger Lakes Partnership for Regional Invasive Species Management (Finger Lake PRISM)
• NYS Department of Conservation
• NYS Office of Parks, Recreation, and Historic Preservation, Finger Lakes Region (OPRHP)
• Racine-Johnson Aquatic Ecologists
• SOLitude Lake Management
• Tompkins County Department of Health
• Tompkins County Soil and Water Conservation District
• US Army Corps of Engineers (USACE) Buffalo Office
• US Fish and Wildlife Service

Control methods used by the Hydrilla Task Force to help control Hydrilla in Cayuga Lake include:

There are two types of herbicides, contact and systemic

Contact

These herbicides kill plants on contact. These treatments are typically used to get a population under control within a short time frame - usually when it is first discovered. Depending on the timing of the application, contact treatments can also prevent the growth of propagules.

Systemic

Systemic herbicides are taken in by the plant gradually and slowly kills it - even the roots. These are used to tackle infestations in the long term.

Each method targets a different part of that species' biology. For instance, a benthic mat can eliminate above ground plant material. But the different control methods have their own drawbacks as well. While benthic mats may be highly effective, they are not feasible to use on large areas. Herbicides can tackle large areas, but, depending on the herbicide used and its concentration, can be harmful to native plants as well. And DASH, while able control parts of the plant above the sediment, is expensive and time consuming.

In controlling Hydrilla, herbicides were found to be the most successful method. Both contact and systemic herbicides would be used to treat the Hydrilla infestation, including endothall and copper-based contact herbicides, and the systemic herbicide fluridone.

In 2018 Hydrilla could no longer be reliably found in the Cayuga Inlet or Fall Creek, and there were no chemical treatments in either area. Over the course of seven years, 166 acres of waterway had been effectively treated for Hydrilla. A contingency was developed to use physical barriers and benthic mats for future populations, but the project had been a success.

Despite the incredible progress made against Hydrilla between 2011-2015, Hydrilla was detected North of Ithaca near Wells College in Aurora, NY in 2016. Surveys were conducted to delineate the extent of the Hydrilla population however the discovery was deemed to be too late in the season to apply herbicide. Therefore the first action taken against this new infestation occurred in 2017.

The following year, partners of the Hydrilla Task Force continued their surveying efforts, and the USACE received funding to control and monitor the site. Fluridone was applied by the USACE in the area highlighted below.

The outcomes of three years of Hydrilla treatment began to show positive results in 2020. The occurrence of Hydrilla in sampled areas decreased from 57% in 2016 to 0.5% in both 2019 and 2020. However, due to the expanding range, the frequency of Hydrilla rebounded to 1.6% in 2021. In 2022, the frequency of Hydrilla detections decreased again to 0.6%, aligning with smaller, sparsely distributed patches in the region. In 2023, Hydrilla detections exceeded 1.2%. The presence of Hydrilla tubers exhibited significant reduction, with a difference of over 99% between 2016 and 2019.

Five miles north of the Cayuga Inlet, an infestation of Hydrilla was discovered at a private marina in Lansing, NY in late August, 2019. Solitude Lake Management was contracted by the Finger Lakes Institute at Hobart and William Smith Colleges to treat the area with Harpoon Granular, a copper-ethylenediamine herbicide in October of that year.

After the copper herbicide treatment in 2019 and weekly fluridone treatments in July 2020, Hydrilla could no longer be detected in the marina, and was only found in the small private pond connected to the marina.

Weekly fluridone treatments continued in July and August of 2021. Monitoring efforts between 6/9 - 9/15 revealed Hydrilla growth throughout the marina, which was not detected in 2020. Although, all the Hydrilla detected in 2021 was still within the treatment area while herbicide levels were effective.

The marina was treated weekly with fluridone again in 2022. Monitoring throughout the marina turned in no detections of Hydrilla, marking the first season without Hydrilla being observed in the marina since the initial discovery in 2019.

Treatment and monitoring will continue in 2023. See map below for locations of Hydrilla detections since 2019.

Sampling for Hydrilla occurs primarily on Cayuga Lake, but extends to the entire Finger Lakes region. Below is a map of all sites sampled for Hydrilla between 2019 and 2023.

The efforts of the Hydrilla Task Force have made treating Hydrilla in Cayuga Lake a major success. While Hydrilla has since spread beyond its initial boundaries from its discovery in 2011, the original and nascent populations are gradually coming under control. Diligent survey efforts, aggressive treatment, and education in the community still lie in the years ahead, but should not undermine the progress that has been made.

A management plan for the entire Cayuga Lake watershed is currently being developed by the partners involved, and it is hoped that this plan will build on top of the work that has already been done to finally eradicate Hydrilla from Cayuga Lake.

If you believe you have found Hydrilla in the Finger Lakes region, please contact FLXplantID@gmail.com with photos and a location!