Hydrilla Project 2015: Proven Approaches & New Strategies

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Tompkins Weekly 11-9-15

By James Balyszak

The transition to fall marks the end of another growing season for local terrestrial and aquatic plant communities. Leaves change color and drop, in a spectacle both brilliant and pleasing to the senses. Crops mature and are harvested to feed communities across the region. Plant communities senesce, as roots and seeds prepare for winter survival until spring arrives next year. It is a dynamic transition, both familiar and reassuring at the same time.

While fall signifies the end of a growing season for native plants, it also signals the end of another growing season. That of the highly invasive aquatic plant hydrilla (Hydrilla verticillata), which the local community has been dealing with since August 2011 after it was discovered in the Cayuga Inlet. With the capability of completely taking over water bodies that it infests, hydrilla can out-compete beneficial native species and impede recreation and commerce by creating thick, choking mats of vegetative growth. The serious threats posed to the Cayuga Lake Watershed by hydrilla required coordinated efforts and swift action to work towards eradication. In response, the Hydrilla Task Force of the Cayuga Lake Watershed (HTF) was formed to spearhead management activities. Since 2011, the HTF has implemented the Cayuga Lake Watershed Hydrilla Management Plan, and is currently wrapping up another treatment season in 2015.

Although treatments were similar to previous seasons, 2015 saw new strategies employed in the fight against hydrilla! Initial application of the contact herbicide Aquathol-K (Aq-K. Active ingredient endothall) was used to address hydrilla biomass (stems/shoots/leaves) above the sediment, while application of the low-dose, systemic herbicide Sonar (active ingredient: fluridone) was used to prevent possible hydrilla regrowth. Herbicide treatments encompassed infestation areas in the Cayuga Inlet, Fall Creek, and for the first time ever the southeast corner of Cayuga Lake.

In coordinating with national peer reviewers to evaluate available management options, the HTF determined that isolated hydrilla patches in the southeast corner of Cayuga Lake posed the greatest threat for potential spread moving forward. As such, a more aggressive and proactive approach was needed. For the first time in the history of the Project, herbicide application occurred in the open waters of the southern end of Cayuga Lake in 2015. Sonar pellets were applied to a 30-acre treatment zone in the southeast corner, which began much earlier in the season; starting on July 21st and extending through October 1st. Sonar treatments within Fall Creek and Cayuga Inlet began on August 26th and September 1st (respectively), and continued through October 12th.

Another change in management strategy involved the application Aq-K using an injection system over a 36-hour period in Fall Creek. By extending application, the HTF and herbicide applicators improved Aq-K target concentration and retention time. This was the first time an extended Aq-K injection strategy had been used in the northeast! Due to the delayed onset of hydrilla growth in 2015, Aq-K treatments did not begin until August 18th and August 25th in Cayuga Inlet and Fall Creek, respectively.

While treatments within the inlet were quite effective and minimal hydrilla growth was observed in the southeast corner of the lake, there was some evidence of hydrilla regrowth in Fall Creek (Fall Creek cove and the golf course lagoon). To address this regrowth, the HTF conducted a small-scale physical removal effort in the golf course lagoon in late September. Members of the HTF removed hydrilla biomass by hand, and nets were used to capture plant fragments created during the removal process. All materials were disposed of offsite. This removal effort was similar to one conducted in Fall Creek cove in September 2014. Having observed success with small-scale physical removal, the HTF will continue to utilize this non-chemical management strategy wherever feasible.

With treatments finalized for the 2015 season, the HTF will continue post-treatment water quality and plant community monitoring through late fall. Treatment updates and plant community reports will follow in early 2016, and the HTF and its stakeholders will begin planning for the upcoming 2016 treatment season!

In addition to active hydrilla management, public education and outreach will be crucial in the fight against hydrilla and other invasive species. HTF stakeholders like Cornell Cooperative Extension, the Cayuga Lake Watershed Network (CLWN), and the Cayuga Lake Floating Classroom lead numerous outreach initiatives. Many opportunities exist for those who want to join the fight against invasives, including volunteering as a Hydrilla Hunter (http://www.cayugalake.org/hydrilla-hunters.html) or participating on hydrilla monitoring cruises aboard the Cayuga Lake Floating Classroom (http://www.floatingclassroom.net/)!

The Hydrilla Task Force would like to thank the community for its continued interest and support this season! As always, further information on the ongoing Cayuga Lake Watershed Hydrilla Project can be found on the official Task Force website (www.Stophydrilla.org).

James Balyszak is Program Manager, Hydrilla Task Force of the Cayuga Lake Watershed.

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