Lake Gaston Treatment & Revegetation Evaluation Component

Background

The Lake Gaston Stakeholders Board (LGSB) Long-term Management Plan has been designed with an objective to reduce the hydrilla coverage (and other noxious weeds) to less than 300 acres by a target period of 2012, while attempting to establish a diverse and healthy native plant community. This objective will likely only be accomplished if a more aggressive approach is taken to exhaust the hydrilla tuber bank.

Review of other monecious hydrilla control programs around the country, reveals two distinct management approaches with aquatic herbicides;
1) Utilizing contact and systemic herbicides (such as the fluridone and copper used on Gaston) to sustain an acceptable non-nuisance level of hydrilla in the waterbody (management of standing crop).
2) Aggressive systemic treatment program (eradication) targeting a reduction both in the standing hydrilla crop and the tuber and turion bank over time.

The Technical Advisory Group (TAG) of the LGSB recommends the implementation of a Treatment and Revegetation Evaluation Component as part of the Long Term Hydrilla Management Program in Lake Gaston. We suggest the LGWCC adopts the following Evaluation program during the 2007 management season with guidance and implementation support from TAG.

Introduction

In order to achieve a reduction in the number of hydrilla acres ), TAG recommends further evaluation of the most appropriate fluridone treatment* approach as part of the long-term management program. This proposal includes a multi-year evaluation of two operational scale fluridone treatment strategies (using Sonar pellet formulations) for targeting hydrilla;
1) Current LGWCC approach of conducting cyclic fluridone treatments ( 2 year cycle)
2) An aggressive hydrilla tuber reduction approach which includes implementing consecutive year fluridone treatments at selected sites.

In addition, native revegetation efforts would be incorporated to selected sites with the objective of evaluating ability of select species to survive within a varied level of hydrilla (and tubers) competition and ability to sustain a long-term diverse plant community in the Evaluation sites.

Methods

" Select a total of 12 sites (eight treatment and four control sites)
Sites would be selected based on the following criteria:
1) Site identified as fluridone treatable areas (coves, creeks, inlets)
2) Sites with existing native plant community (per ACOE or other surveys)
3) Conditions that would likely support native plant establishment (sediment/nutrient characterization)
4) Sites not treated with fluridone during the 2006 season (due to lack of pre-evaluation tuber data)
" 4 sites (A-D) would be treated using the 2 year cycle approach (i.e. treat in 2007 and again in 2009)
" 4 sites (E-H) would be treated a minimum three consecutive years (i.e. 2007, 2008, 2009)
" 4 control sites, no historic and future fluridone treatments 2007-2009 (sites with no known fluridone history and no or limited contact herbicide treatments)
" Remaining hydrilla management sites targeted for fluridone would continue on 2 year cycle (or 3 year cycle per budget and LGWCC direction).
" Spring and fall hydrilla tuber & turion monitoring, to include general sediment characterization in 2007. An additional tuber and turion monitoring event (winter) would be conducted after tuber drop from floating mats, as budget allows. Three monitoring events would help determine the potential regrowth from onsite tubers compared to those transported and deposited from floating mats.
" Planting of native plants (species and location TBD).
" Annually evaluate (October) native plant establishment (augmented and natural) and hydrilla population in Evaluation sites.

Discussion
Upon assessment of the monitoring data for the ten evaluation sites (winter 2009), TAG would provide general recommendations as follows:

1) Adopt consecutive year treatment approach. If consecutive multi-year approach recommended, discuss the plan for continuing treatments/monitoring in the existing four Evaluation sites (E-F) to exhaust tuber & turion bank in the coming years. This approach could include;
A1) treating the entire site with Sonar, as with previous three seasons
A2) spot-treating hydrilla areas within the site, with Sonar (based on spring surveys)
Also begin to select other sites to initiate the consecutive year fluridone approach in 2010. Modify the level and location of grass carp stocking to complement the invasive and native plant community objectives.

2) Provide adaptations (if any) to "cyclic" fluridone treatment approach and revegetation components for future seasons. Continue with 2 (or 3) year cycle approach and incorporate revegetation efforts where appropriate. Modify the level and location of grass carp stocking to complement the invasive and native community objectives.

3) Suggest a revised long-term management objective for Lake Gaston. Need would be based on TAG's review of management status to date, Evaluation site data and ultimately the groups expert opinion if the current objective remains achievable (from a technical and funding perspective). If the answer is no, then outline a new objective from a technical and funding perspective. Modify the level and location of grass carp stocking to complement the current lake management objective or the new objective as it relates to invasive and native plant community objectives.

* Currently fluridone (Sonar) is the only registered systemic herbicide for large scale management of hydrilla. TAG intends to evaluate new systemic herbicides as they become available for operational control. TAG will review the new technology and where appropriate incorporate these tools into the long-term management plan and/ or Evaluation component.


Estimated Annual Evaluation Program Costs

1) Tuber and Turion Sampling $40,000 (Spring & Fall) or $50,000 (Spring, Fall, Winter)
- Conduct hydrilla tuber/turion sampling in each of 12 Evaluation Sites (Spring and Fall), methods and locations would be defined further by TAG.

2) Treatment/Control Site Assessment $10,000
- Annually evaluate (fall) hydrilla and native plants in all LGWCC management areas (including 12 Evaluation Sites) via point intercept method history utilized by Madsen. A whole lake plant survey (invasive and native plants) would be conducted independent of this effort. Methods & cooperators should be further defined by TAG and LGWCC prior to start of 2007 management season. The Treatment Site Assessment and Whole Lake plant survey efforts could be combined to a single monitoring event in Oct/Nov. Cost for a single plant monitoring event is estimated at $40-50,000, pending survey method(s) selected. In previous year, LGWCC has budgeted approximately $35,000 for both Site Assessment and Whole Lake plant surveys.

3) Revegetation Component $ ???
- Planting of native plants (species and location TBD) to assessment ability to survive competition by hydrilla, establish in previously treated areas and survive low dose fluridone treatments. Cooperate with ACOE as funding and availability allow. If current federal (USDA/ACOE) funding is not available in future years, revegetation expenses would have to be absorbed by the LGWCC or covered by external funding, which LGWCC would need to actively pursue.