Rapid response: Rapid response efforts should focus on the use of a contact herbicide that controls hydrilla relatively quickly by damaging the parts of the plant that it directly contacts. Successful rapid response requires coordination with regulatory agencies and regulators that are willing to streamline permitting processes, where feasible. Existing permitting processes in many states have review and public notification timeframes that hamper the ability to treat hydrilla quickly. Thus, states should develop a streamlined permitting process that facilitates rapid response upon detection. Such a “rapid response” permit should be considered by state agencies for treatments under 3 acres to provide leeway for managers to quickly address new infestations.
Long-term Sustained Control: Based on successful eradication programs in other parts of the country (e.g., Maine, California, and Washington), we know that eradication is a multi-year effort and requires a long-term commitment. Since successful eradication programs often have more than five years of treatment, it is important to obtain support from agencies and project proponents, as well as a sustained funding source. The first year or two of treatment in an eradication program is the most critical in decreasing overall hydrilla biomass and reducing the number of hydrilla fragments by orders of magnitude, which reduces the chance for further spread. Typically, years three through eight of a treatment program are designed to control the last one to five percent of the tuber bank. In later years, it becomes increasingly difficult to eliminate the final one to two percent of the tuber bank, as detection becomes difficult.
Herbicide application is the most effective means of hydrilla management in the Great Lakes. Grass carp have been implemented on a much lower frequency in small water bodies, used in concert with herbicides, and used to manage lower level infestations . The U.S. Army Engineer Research and Development Center is currently researching possible biocontrol agents for monoecious hydrilla, but no such agents are currently available. Mechanical controls are not a preferred management option unless the infestation is limited to a small patch of hydrilla that can be isolated with a curtain. Mechanical controls can be costly, labor-intensive, and result in extensive spread of plant fragments.
With effective, long-term, sustained control, hydrilla can transition to isolated patches/satellite populations that survive treatment or re-sprout from the bank of subsurface tubers. For these isolated patches, the following approaches have been documented to be effective:
- Apply contact herbicides at the maximum label rates, along with limited public access in those areas;
- Use benthic mats (i.e., burlap barriers) on very small patches of hydrilla in shallow, low-velocity water. Due to cost and labor requirements associated with installation, benthic mats are not feasible for use in larger areas; and
- Use limnocorrals (impermeable enclosures) to isolate hydrilla beds for direct application of herbicide. Limnocorrals have been shown to be effective, but are also labor intensive.
Hydrilla can be found in a variety of systems, from lakes and reservoirs to flowing streams. Identifying the most effective treatment plan for each site is a case-by-case exercise. Refer to the Case Studies page for examples of management in various systems.