BUFFALO, NY—The U.S. Army Corps of Engineers, Buffalo District completed a scheduled herbicide treatment of the invasive Hydrilla plant in Cayuga Lake near Aurora, NY in late July 2017, having previously conducted a plant survey in the location the last week of June and again on July 17, 2017.
The Corps of Engineers is authorized to treat Hydrilla (hydrilla verticillata) under Section 104 of the River and Harbor Act of 1958, through the Aquatic Plant Control Research Program. Funding for the project is available through the Corps of Engineers Aquatic Plant Control Research Program and Great Lakes Restoration Initiative. In the absence of control measures, the highly invasive plant crowds out native vegetation, diminishes the habitat available for fish and wildlife, and impedes boating and recreational use of the waterway. The Hydrilla’s presence in Cayuga Lake was discovered in late summer 2011 near Ithaca and has only recently appeared in the Aurora area in September 2016.
The survey work performed on July 17 was extensive, as over 350 samples were collected. Thunderstorms halted work around mid-day, but the crew was able to return to the water by the early afternoon. Collecting the samples involved two simple methods. The first collection method involves a metal rake, which looks like the bottom of a rake you might use in your garden. The team of biologists would cast the rake attached to a rope out into the lake. The team then drags the rake across the lake bottom to collect the plant samples. Sample rakings would bring up a mixture of species such as muskgrass, starry stonewort, white stem pondweed, sago pondweed, eurasian water milfoil, Canadian waterweed, and of course, Hydrilla.
“The big distinguishing feature of the Hydrilla is the serration on the leaves,” said Michael Voorhees, the other Buffalo District biologist assigned to the project. “In some of the younger plants, there are whirls of three leaves. In our sampling today, we found Hydrilla with the tubers attached, which embed themselves into the sediment.”
The second method of collection involved a nearly 15-foot long coring instrument made out of PVC materials, which staff use to dig into the sediment on the bottom of the lake in order to sample a plug of sediment approximately 4” in diameter and at least 6” deep, and bring it to the surface. After the samples are extracted, the sample is dumped into a wash station and filtered to determine if any hydrilla tubers are present and to document the growth stage.
In anticipation of the herbicide treatment, Corps of Engineers biologists met with the community at the Village of Aurora Board meeting in June to discuss their plans and to field any questions related to the chemicals being used and the area assigned for coverage.
The Corps of Engineers’ contractors used two EPA-approved herbicides, Sonar® and Komeen®, which Buffalo District biologist Rich Ruby says is safe and has been used for many years, including previously in the southern part of Cayuga Lake near the inlet. Prior to making the decision to use herbicides, the team went through a formal environmental review process to explore alternative eradication methods.
Removal of invasive species can sometimes be done by physically removing them, said Rich Ruby. But for plants like the Hydrilla, which can spread from plant fragments that have broken off of rooted plants that were disturbed (e.g. boating or mechanical harvesting) can actually help them spread. Herbicides, therefore, are the most effective way of eliminating the invasive plant without running the risk of assisting in its propagation.
With mechanical removal of the plants off the table, another option was to use “benthic mats”, made from the same material used in gym floor mats. Placing mats down on the lake floor would stifle weed growth. However, because of the wide coverage in the Cayuga Lake project, the mat option would be expensive. Ruby explained that the plants were found at water depths close to shore but as far out as 18-foot depths, covering a 27-acre area in the near-shore littoral zone of Cayuga Lake.
The herbicides were applied in a pellet form and they are safe for fishing and swimming, and at the concentration levels they were using it at, says Ruby, they are also safe for irrigation. Incidentally, swimming near the Wells College boat house and dock was closed for the day on of the herbicide treatment because of NYS Department of Health concerns about an algal bloom.
The Corps of Engineers will monitor the progress of the herbicide treatment at Cayuga Lake over the next few months. The team will also be treating areas of the Erie Canal during the last week of July. To check out a video of the surveying process or to see the herbicide application, visit https://youtu.be/BgvMtY1Lg2w.