Integrated Plant Management
In the final phase of the Hydrilla Issues Workshop held December 7, 2004 the participants listed Integrated Aquatic Plant Management as one of the top five issues. Integrated Aquatic Plant Management is the process of evaluating all available tools and then using the appropriate tools in a combination that will achieve the management objectives for a given aquatic system and a given budget. There are several written descriptions in reports and manuscripts that describe this management strategy. The following summary outlining Integrated Aquatic Plant Management is from the North American Lake Management (NALMS)/Aquatic Plant Management Societies’ (APMS) aquatic plant management manual (Hoyer and Canfield 1997):
A successful integrated aquatic plant management plan is built on six main principles: (1) identify the uses of the water body and determine if any of these uses are impaired or benefited by aquatic vegetation; (2) understand plant ecology and the ecology of the water body; (3) set management goals; (4) consider all management techniques and select for use those that are most appropriate for the defined problems; (5) develop an action plan and a program to monitor the success or failure of management activities; (6) establish a long-term aquatic plant management education program.
The Department of Environmental Protection and other agencies charged with the management of aquatic plants generally follow the above procedures with some exceptions that came out in the Hydrilla Issues Workshop.
Throughout the workshop it became obvious that for the above Principle (4) the number of tools that are available for aquatic plant management is declining, especially for large lakes with abundant hydrilla that is resistant to low concentrations of fluridone. This hinders the ability to use fluridone for the selective control of hydrilla and enhancement of native plants. Fluridone provides short-term control of resistant hydrilla at higher use rates, but at an increased risk of killing non-target plants and at a significantly higher cost. Thus, to maintain some level of control, other management methods like contact herbicides and/or mechanical harvesting will have to be used, understanding that the total area of hydrilla control will be much less for equivalent expenditures. More information and some recommendations to alleviate this problem will be made in the section on herbicides.
The workshop participants strongly felt that the above noted procedures need to be followed working toward the development of lake management plans making sure to involve all stakeholders. Developing individual lake management plans by incorporating stakeholder input can be accomplished (e.g., Tsala Apopka Chain of Lakes, Hoyer et al. 1999). However, this is time consuming and requires dedicated financial resources.
Integrating Mechanical or Biological Control Methods
While this document provides detailed discussions and recommendations for grass carp, chemical use, and water level deviations, there is limited mention of mechanical and classical biological control approaches. Workshop participants suggested that moving towards an integrated management approach was the number one issue and priority, yet there was little input regarding how to incorporate mechanical or biological control methods with the current management techniques. Both mechanical and biological control were noted as tools that may be used for hydrilla control, yet both options have been available for many years and technological advances that demonstrate methods for improved use of these tools are limited.
The lack of discussion on mechanical harvesting likely reflects the fact that there have been limited advances in technology over the past several decades (Haller 1996). While mechanical harvesting can provide immediate relief from hydrilla, the typical cost of control ($500 to $1,200 per acre), limited capacity to address large-scale infestations, and rapid re-growth of hydrilla have greatly limited the use of harvesting as a primary tool for hydrilla control. It should be noted that as the potential for integration of mechanical harvesting is discussed, in-lake disposal methods could significantly increase efficiency and reduce costs by up to 50% compared to standard trucking and disposal methods (Sabol 1981). While recent evaluation of a machine called the Kelpin harvester provided hydrilla control at approximately $200 per acre (Haller 1996), these large machines can be difficult to move from site to site, and the upfront costs for building the number of machines necessary to integrate this technology into a statewide program would be substantial. Lastly, a significant increase in the use of harvesting suggests the issue of non-target organism mortality as described by Haller et al. (1980) would need to be revisited. While mechanical harvesting represents a tool that could be immediately integrated into the larger state hydrilla control program, issues such as cost-effectiveness, use patterns and efficiency, non-target impacts, and disposal methods would require further discussion prior to embarking on a large-scale mechanical control effort.
Classical biological control has a much better chance of providing a long-term and highly selective tool for hydrilla control; however, overseas exploration for new organisms has been very limited over the last decade. The Hydrellia flies Hydrellia pakistanae and Hydrellia balciunasi have been released in Florida for the control of Hydrilla. H. pakistanae became established, while H. balciunasi has not. While research with H. pakistanae continues, there is limited evidence that demonstrates presence of the hydrellia fly provides a consistent and quantifiable level of control that is compatible with an operational management program. Hydrellia flies are already present in many lakes throughout Florida, and their effectiveness is related to the ability to build up a threshold population density (Wheeler and Center 2001). Fly populations are impacted by both winter weather patterns as well as the nutritional value (nitrogen) of the hydrilla, with damage typically noted in the top 20 cm of the hydrilla canopy (Wheeler and Center 2001). Lake Seminole on the border of Florida and Georgia does represent a site where H. pakistanae populations are thought to have increased to a level that provided a large-scale, but short-term reduction in hydrilla biomass (Grodowitz et al. 2003b). Nonetheless, at the current time, the presence or absence of the hydrellia fly within a waterbody has little bearing on the hydrilla management approach taken by resource managers in Florida. From an integrated plant management standpoint, the presence of hydrellia flies is likely having some level of impact on hydrilla growth potential (Doyle et al. 2002), and therefore, where present, the hydrellia fly would already be considered part of an integrated management program.
The operational use of this tool as a primary means of managing a hydrilla infestation remains a significant question. There has been a recent research emphasis on mass rearing and release of hydrellia flies to provide a more pro-active approach to hydrilla management, and these results are being analyzed. Results from laboratory and the field indicate that herbivory by Hydrellia spp. can impact hydrilla by reducing photosynthesis, thereby impacting biomass production and tuber formation. This research suggests that sustained herbivory, even at relatively low levels (i.e., 15% to 30% leaf damage) may reduce the competitive advantage of hydrilla over native species allowing native species to compete more favorably (Doyle, et al. 2002, Grodowitz et al. 2003 and Grodowitz and Smart et al. 2003).
Researchers from the U. S. Army Engineers Engineer Research and Development Center (ERDC), Vicksburg, MS have continued work with H. pakistanae in the laboratory and field and they have developed mass rearing capabilities. Mass rearing allows introduction or augmentation of Hydrellia sp.. Researchers with the ERDC are currently working with the Florida DEP regarding permits for releasing Hydrellia flies into selected Florida Lakes. In addition to releasing the flies, there are plans for follow-up monitoring of hydrellia fly populations and their impact on hydrilla. It should be noted that it might take a number of years and a number of fly introductions for impacts to be seen and documented.
As research with the hydrellia fly continues, aquatic resource managers in Florida should pay close attention to results that provide a quantifiable demonstration of the effects of site augmentation with the flies.
Due to the limited number of classical biological control options available, aquatic resource managers within the state of Florida should encourage interested agencies (FLDEP, USACOE, University of Florida) to meet and discuss the feasibility, advisability, and target countries for renewing overseas searches for biological control organisms on hydrilla. While the performance of the upcoming hydrellia fly augmentation releases will be monitored, to date, H. pakistanae has not been indicative of an organism that will provide a predictable level of hydrilla control necessary to relieve pressure on aquatic managers.
Recommendations
Recommendation 1: Florida Department of Environmental Protection (FDEP) should begin establishing for each lake/aquatic system receiving significant State of Florida aquatic plant management funds an initial working group composed of senior FDEP and Florida Fish and Wildlife Conservation Commission (FWC) staff that is charged with developing a preliminary, written, aquatic plant management plan. Other appropriate state and federal agencies will be notified of the formation of this working group and those agencies will be allowed to determine whom among their staff are best qualified to provide input on the development of the plan. The plan must consider the principal or planned use of the water body, the optimum sustained use by the public of the water body’s living aquatic resources, and/or sound biological management principals. The working group must utilize stakeholder input throughout the development of lake management plans. Finally, the working group shall also determine the historical level of hydrilla infestation, current status of the hydrilla, and technologies and funding available for control when determining the minimum feasible level of hydrilla. This must be done with the recognition that protection of human health, safety, and recreation are mandated by the Florida legislature when determining minimum feasible levels of hydrilla.
Justification: The Florida Department of Environmental Protection and the Florida Fish and Wildlife Conservation Commission are the two entities charged by the Legislature to manage aquatic plants throughout the state of Florida. Senior staffs from these two groups know the lakes, have extensive experience, and know other pertinent players at each lake. Senior staff of these agencies in conjunction with appropriate representatives from other local, state, and federal agencies has the best chance of coming up with a temporary yet workable lake management plan. These individuals also know the consequences of failure (i.e., legislative involvement) to their programs. Both the FLDEP and FWC have statewide responsibilities regarding hydrilla management, therefore, these two groups will be the most knowledgeable regarding the need for including Water Management Districts, the US Army Corps of Engineers, US Fish and Wildlife Service, County cooperators, and other groups with a stake in management policies regarding hydrilla.