EPA Workplan: Demonstration Project on Hydrilla and Hygrophila in the Upper Kissimmee Chain of Lakes

Element 2: Evaluation of Currently Registered Herbicides for Control of Hydrilla and Hygrophila

Objectives Addressed by Element 2

1) To evaluate new technology processes or practices, or a new combination or uses of technologies, processes or practices for the control of hydrilla and hygrophila using small-scale field work.

2) To implement and monitor successful practices and processes identified in objective 2 using large-scale field demonstrations.

Introduction for Hydrilla

Of the nine active ingredients currently registered for aquatic use, only four of these compounds (fluridone, endothall, diquat, copper) have been proven effective for hydrilla (Hydrilla verticillata) control. The products that form the backbone of most state-funded hydrilla control programs include fluridone and endothall.

Fluridone is a slow acting herbicide that prevents the formation of carotenoid pigments. This results in bleaching of newly developing plant tissue, and ultimate control of the plant due to its inability to produce healthy new shoot tissue. Following large-scale and repeated use of fluridone in the Kissimmee Chain of Lakes ( Osceola County), hydrilla has developed an increased resistance to this herbicide. This increased resistance has resulted in a significant cost increase, reduced longevity of control, and increased non-target plant injury due to the requirement for higher use rates. Due to the widespread coverage of fluridone resistant hydrilla in the Kissimmee Chain of Lakes, spread of this biotype to other water bodies within Osceola County is inevitable.

Endothall is faster acting contact-type herbicide that disrupts plant membranes and respiration resulting in loss of tissue integrity and ultimate collapse of the standing mass. This product has been available since the early 1960’s and has generally proven reliable for the short-term control of the standing mass of hydrilla. Due to issues noted with fluridone resistance, endothall use in the FLDEP state program within Osceola County has increased significantly over the past few years. The increased use pattern of endothall has many resource managers asking questions regarding optimal use patterns as well as potential strategies to treat in higher flow or shallow water environments that can tend to limit the efficacy of this product.

Approach

Due to the limited number of registered products, we propose that work on hydrilla control should be focused in the following areas:

  1. Evaluations of endothall in high flow areas of the Kissimmee Chain of Lakes or in other Osceola County Lakes where drip applications can be evaluated.
  2. Evaluations of endothall use in the fall and winter for control of hydrilla.
  3. Evaluations of endothall in shallow-water environments, with an emphasis on initial efficacy and longevity of control.

The proposed projects will generally include initial laboratory (replicated trials inside) or mesocosm (replicated trials outside) validation work, followed by field-scale demonstrations using the most promising techniques. We have decided that while fluridone does represent an existing and important technology, knowledge on use patterns for both fluridone-resistant and fluridone-sensitive strains of hydrilla is extensive within Osceola County. We feel there is a much greater need to focus our attention on developing information on the other existing molecules to help us reduce our reliance on fluridone.

 

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Element 2,Task 1: Evaluations of endothall in high flow areas of the Kissimmee Chain of Lakes or in other Osceola County Lakes where drip applications can be evaluated.

Objectives

1) To evaluate new technology processes or practices, or a new combination or uses of technologies, processes or practices for the control of hydrilla using small-scale field work.

2) To implement and monitor successful practices and processes identified in objective 2 using large-scale field demonstrations.

Justification

The reduced activity of fluridone for larger scale hydrilla control and the recent increase in the use of endothall has many resource managers asking questions regarding the expansion of endothall applications into larger areas that have traditionally presented challenges to achieving control. There are several areas on the Kissimmee Chain ofLakes (Tohopekaliga, Cypress, Hatchineha, and Kissimmee) and other Osceola County Lakes that are subjected to significant water movement due to scheduled water releases. Areas currently identified include East City Ditch/ Mill Slough inlet and Goblet’s Cove on Lake Tohopekaliga, the SW corner of Lake Cypress that receives water from the Lake Tohopekaliga outlet structure, the NE lobe of Lake Hatchineha, and the outlet of Lake Jackson. As these areas represent high-flow zones in the lakes, control of the more tolerant strains of hydrilla with fluridone has been challenging. There is ongoing discussion between aquatic plant managers and engineers regarding the flood control threat that hydrilla poses when it forms dense infestations near the areas described above. We feel that an evaluation of an endothall drip treatment, a little used technology that needs refinement, in these zones is warranted as it could provide improved control of hydrilla by delivering a target concentration of endothall for a defined period of time. These high-flow environments have posed challenges to traditional application techniques due to rapid dispersion of the residues from the treatment area.

Approach

Although some notable differences exist, these proposed treatments would be similar in nature to the endothall treatments being conducted by the Florida Department of Environmental Protection on Wakulla Springs. The proposed sites provide the ability to drip endothall into a fairly narrow channel that widens to a broader area. While this aspect of the treatments represents a departure from the Wakulla Springs applications (injection into a long narrow river channel), it is anticipated that during the 48 to 96 hour injection, the treated water will spread laterally throughout the target zone.

To demonstrate the principle of chemical dispersion, it is suggested that in some areas a short-term Rhodamine Wt dye study (up to 48 hour injection) be conducted to determine chemical dispersion downstream from the injection point. Good dispersion of dye outside of the main channel would strongly support endothall drip applications. In addition, the downstream movement patterns of the dye plume will provide data that can be used to plan the duration of the drip application. If the water moves as a slowly diluting plume, then the area of control could be much greater than the actual amount of water treated.

As endothall treatments are implemented, we plan to establish monitoring protocols for endothall residues via the use of an enzyme-linked immunoassay (ELISA), and subsequent monitoring of hydrilla control and native plant response via point intercept methods. The ELISA can detect endothall to a concentration of 7 ppb (typical use rates are 1500 to 3000 ppb) and will be key to this demonstration, as it will allow us to compare treatment results across different sites. We know that the key to achieving hydrilla control with endothall relates to the concentration and exposure time scenarios that are achieved. The ELISA will allow us to determine these scenarios for each demonstration site and this will allow us to come up with guidance regarding drip treatment scenarios for the different treatment sites. There are several pros and cons to this approach.

Pros

  1. Application costs will be minimal to non-existent compared to traditional endothall pellet or liquid applications.
  2. Use of liquids on a large scale will be more cost-effective than pellet applications.
  3. Treatment of incoming water will result in good top to bottom distribution of endothall residues. This provides control of the root crown as well as the shoots.
  4. Applicator exposure will be minimized by this approach
  5. Conducting treatments in the fall, winter, or spring will greatly reduce microbial degradation of endothall, allowing better downstream movement of residues.
  6. Hydrilla die-back will be much slower during fall, winter and spring than in the summer, and treatment of the plants in flowing water will mitigate any concerns with water quality.
  7. Treatment of cool water decreases negative impacts of oxygen depletion from plant decomposition (decreases chance of fish kill).
  8. Treatments can be timed based on favorable weather patterns. No need to schedule helicopter time and a crew for filling hoppers.
  9. Use of endothall immunoassay will allow us to determine the actual dispersion pattern and longevity of the endothall residues.
  10. If this approach works well, it should be sustainable, as the flowing water system will prevent the buildup of a microbial flora that can rapidly degrade endothall.

Cons

  1. It is not possible to predict the longevity of control, but we would like to achieve 6 to 9 months of relief from hydrilla.
  2. There will be a fishing restriction associated with the application. Upcoming EPA action on endothall label may preclude these restrictions.
  3. Vandalism to the drip equipment or theft of chemicals is possible.

This technology will have potential applications for other high-flow sites in the State of Florida such as Lake Rousseau, Lake Seminole, and Lake Istokpoga.

 

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Element 2, Task 1 Milestones and Measure of Success

Fall of 2006 and Spring of 2007: An injector system will be constructed in the Fall of 2006 and treatments will be scheduled for November 2006. A preliminary dye study will be conducted to provide a prediction of herbicide dispersion patterns by December 2006. This short-term study will allow us to determine appropriate use rates and duration of the drip application. If the initial demonstration is successful, other areas that can benefit from drip application technology will be evaluated, and further treatments will be scheduled in October through March in both 2007 and 2008.

Residue, efficacy, and selectivity data collected during this effort will be written up as a manuscript and submitted for peer-review publication. The project evaluates and documents, a little used technique fro controlling hydrilla in flowing waters. New information should lead to better long-term control at a reduced cost and with minimum applicator exposure. If we demonstrate this technology to be superior to current strategies, we will continue to refine use rates and timing to provide optimal hydrilla control.

 

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Element 2, Task 2: Evaluations of endothall in shallow-water environments, with an emphasis on initial efficacy and longevity of control.

Objectives

1) To evaluate new technology processes or practices, or a new combination or uses of technologies, processes or practices for the control of hydrilla using small-scale field work.

2) To implement and monitor successful practices and processes identified in objective 2 using large-scale field demonstrations.

Justification

The FDEP does not currently manage hydrilla in waters of less than 3 feet in depth due to perception that the control achieved is of very short term and due to the fact that the Kissimmee Chain of Lakes (KCOL) can fluctuate by as much as 4 to 5 feet a year based on water regulations, seasons and prevailing weather patterns. Nonetheless, leaving this hydrilla unmanaged results in large contiguous shallow littoral zones of the lake that are dominated by hydrilla. These plants serve as a source of re-infestation of managed areas as well as creating access problems for many users of the lake.

Osceola County personnel have been tasked with developing an integrated plan to manage hydrilla in these shallow areas, and it is our intent to develop treatment protocols in conjunction with County operations that will evaluate treatment timing, use rate, size of the treatment block, and the herbicide formulation. Endothall is currently the only effective contact herbicide approved for use on hydrilla. Current use patterns in the shallow littoral zones include long and narrow shoreline strip applications that are thought to result in rapid dispersion of the endothall molecule from the treatment zone. These short-term exposures result in reduced treatment efficacy and rapid re-growth of the hydrilla.

Approach

In order to protect drinking water wells that may be seated in a surficial aquifer, a survey will be conducted to identify these drinking water wells within a mile of the lake application site. Should any such wells be identified, no treatment shall occur until the EPA Project Manager is notified and provides approval.

To assure that detention stormwater pond test sites do not result in drinking water well contamination, prior to applying registered or experimental use herbicides, Osceola County will inspect stormwater ponds to verify that they are in good repair and meet the permitted design standards.

Water residue sampling behind operational treatments has not been feasible in the past due to the high cost of sample analysis. Through the use of ELISA technology, intensive sampling will take place within the zones of treatment and outside the treated areas to determine if current application strategies are responsible for the reduced control in the shallow zones of various water bodies. Coordination will occur with Osceola County managers to determine areas in the County that would benefit from shallow water applications of endothall for control of hydrilla. Sampling stations will be established via GPS coordinates, and these sites will be sampled over a 3 day period following application. Residue data will be correlated with pre and post-treatment plant frequency and biomass. Plant biomass and frequency will be collected prior to treatment and at 6, 12, and 24 weeks after treatment.

Shallow water applications can be conducted during almost any time of the year. Evaluation of 2 to 5 shallow water operational applications in the fall of 2006, the winter/spring of 2007, the summer of 2007 and the fall of 2007. During this time, coordination between Osceola County personnel and UF/ IFAS staff will be critical to alter treatment strategies if the early residue and efficacy data suggest that treatments are failing due to the inability to maintain a phytotoxic level of herbicide for the required period of time.

Refinement of application techniques and use rates and focus on demonstrating optimal treatment strategies will continue. These demonstrations will require continued sampling of numerous operational applications (2 to 5 applications during each season) throughout the year. If we observe poor control following conventional treatment strategies based on an inability to maintain the necessary concentration and exposure requirements, we will develop different treatment strategies with Osceola County personnel. Strategies may include increasing the width of the strips, changing to granular formulations, changing target concentrations, or treating in cooler water when microbial degradation rates are slower. We will continue to conduct intensive residue sampling and efficacy assessments to determine optimal technologies for improving initial efficacy and longevity of hydrilla control in shallow littoral zones. As Osceola County personnel have been tasked with maintaining control of hydrilla in many of the shallow zones, we will coordinate closely to insure that our sampling occurs immediately behind the operational treatments.

 

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Element 2, Task 2 Milestones & Measure of Success

In the fall of 2006, coordination between Osceola County managers and UF staff in the determination of areas in the County that would benefit from shallow water applications of endothall for control of hydrilla. Evaluation of 2 to 5 shallow water operational applications will occur in the fall of 2006, the winter/spring of 2007, the summer of 2007 and the fall of 2007. Continued to refinement of the application techniques and use rates and focus on demonstrating optimal treatment strategies will be addressed in 2008 and 2009. The measure of success in this task is evaluating and providing information to Osceola County that will increase the efficacy and longevity of shallow water endothall treatments.

Element 2 Continued - Introduction: Hygrophila Control

Of the nine active ingredients currently registered for aquatic use, none of these compounds has been proven to be highly effective for hygrophila (Hygrophila polysperma) control in high-flow environments (Table 2). There have been some herbicide efficacy evaluations on hygrophila in South Florida, but the results have been equivocal, and successes difficult to replicate. At this point in time, most of the chemical control methods implemented for hygrophila are based on trial and error and anecdotal evidence of control. Current recommendations suggest that repeat applications are necessary, and the frequency of these repeat applications can often come at very short intervals. The vast majority of hygrophila control efforts have been focused in the canal systems of South Florida, and there is limited experience with controlling this plant in other areas of the state. The lack of success with currently registered compounds suggests the need for new active ingredients; however, expansion of treatment strategies with current compounds warrants further evaluation.

As hygrophila is found mainly in high flow environments (canals, creeks, areas of lakes subject to high flow events), traditional herbicide applications to a discrete treatment zone likely results in rapid dispersion of the residues to downstream sites. While the failure of registered herbicides to provide control in many situationslikely speaks to the fact that hygrophila can be fairly tolerant of herbicide applications, the rapid downstream movement of residues is a confounding factor. At the present time there is very limited information regarding the efficacy of registered compounds on hygrophila under controlled Concentration and Exposure Time (CET) evaluations. This type of evaluation is critical to determining treatment strategies and which herbicides will work the best in a given environment.

 

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Element 2, Task 3: Evaluation of diquat, endothall, 2,4-D, and triclopyr under controlled conditions to determine the CET requirements for each compound and formulation.

Objectives Addressed by Element 2

1) To evaluate new technology processes or practices, or a new combination or uses of technologies, processes or practices for the control of hygrophila using small-scale field work.

2) To implement and monitor successful practices and processes identified in objective 2 using large-scale field demonstrations.

Justification

Development of CET requirements for numerous invasive aquatic plants (e.g. hydrilla, Eurasian milfoil, egeria, sago pondweed) has proven to be highly transferable to field conditions. These relationships have allowed us to change application strategies for compounds such as fluridone and endothall, and can explain our lack of ability to achieve control under certain environmental conditions. The lack of this information to date has resulted in numerous field trials that have yielded very limited information. We plan to screen each of the compounds noted above in a systematic manner to determine if hygrophila is truly tolerant to the herbicide, if a rate-response exists, and if maintaining longer-term exposures at reduced use rates can increase the efficacy. We will also compare liquid and granular formulations of 2,4-D, endothall, and triclopyr to determine if efficacy differences exist.

Approach

Due to the limited information we have on hygrophila response under controlled conditions, we propose a two-tiered approach to evaluation of currently registered compounds. Work on registered products for hygrophila control should be focused in the following areas:

  1. Develop culture methods for hygrophila that allow small-scale efficacy testing of registered herbicides
  2. Evaluation of diquat, endothall, and 2,4-D, which are registered herbicides and triclopyr, which has section 3 approval under controlled conditions to determine the CET requirements for each compound and formulation.
  3. Field evaluations of the most promising compounds and application strategies in Osceola County.

Studies will be conducted in small outdoor mesocosm facilities or in growth chambers. Herbicides will be evaluated under a variety of Concentration and Exposure Time scenarios that would be likely given high-flow conditions. Exposure times will range from 1 hour up to 72 hours, and herbicide rates evaluated will increase incrementally up to the maximum label rate. This is a well-established approach for evaluating herbicide efficacy on other aquatic species, and several peer-reviewed papers have been published describing the various CET relationships that exist for a given herbicide and target plant species. Certain compounds that show promise in the mesocosm testing will be recommended for further evaluation at the field scale in a high-flow environment to validate work conducted at the mesocosm scale. Herbicide residue and efficacy data will be collected.

Large-scale field evaluations and test plot will be performed in Osceola County for the most promising. This information will be highly useful to both Osceola County and to water managers responsible for maintaining weed-free flood control canals in South Florida.

 

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Element 2, Task 3 Milestones

Existing registered products and EUP products will be screened during years 1 and 2 of the project. Products that show little potential for performance will be removed from further consideration. Starting in year 2 and continuing through year 3, we will select the products that have the optimal efficacy and environmental characteristics for more intensive testing at the mesocosm scale. Based on results from the mesocosm trials, field-testing will be initiated in year 2 or year 3. Following data collection, reports will be provided on the optimal product or product combination that provides control of Hygrophila in a high-flow environment.

Overall Timeline for Element 2

 

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