Great Lakes Hydrilla Collaborative
Recommendations for Prevention, Detection, and Response

Prevention

Prevention

The first step to prevent the spread of hydrilla is public education directed toward water users, including passive recreation users, boaters, and fishermen. It is important to share information about the potential impacts of hydrilla, and what can be done to reduce the risks associated with transport. Two key recommendations for public awareness are provided below.



Number 1

Develop a public information campaign to educate the public, specifically recreational water users, on what hydrilla is, how to identify it, and the threat it poses to the Great Lakes.

Education

This recommendation focuses on public education through development of hydrilla-specific targeted outreach and educational materials, drawing upon existing regional and national program materials, and using existing venues to distribute the materials. Examples include distributing materials at public and private marinas and botanical gardens, organizing lake management and angler association membership mailings and events, developing state aquatic nuisance species programs, and conducting workshops implemented by Partnerships for Regional Invasive Species Management (PRISMs).

Outreach and educational materials should include the following content to be most effective:

  • Information on how to identify the plant and how to distinguish it from native plants. The Hydrilla Hunt! ID sheet and ID card are examples of identification materials.
  • An overview of hydrilla’s potential impacts if it successfully establishes in the Great Lakes and the importance of diligence with respect to early detection efforts.


number 2

Post signage at all access points and implement watercraft inspections at areas of high traffic or at highest use boat ramps within priority public watercourses.

Recreational boating has been identified as a key pathway in the spread of aquatic invasive species (AIS) across the Great Lakes Basin including inland waterbodies (Rothlisberger et al. 2010; Hebebrand and Bossenbroek 2017). Signage, watercraft inspections, wash stations, and nuisance species disposal stations should be provided with priority given to already infested waters, waters with high boater activity, and waters in proximity to existing infestations. Watercraft inspection should be limited to those areas of highest traffic or the highest use boat ramps within a priority public watercourse. Inspection consists of visually inspecting all areas of boating and recreational equipment (e.g., boats, trailers, motors, livewells, anchors, snorkeling and scuba gear, and paddles) that come into contact with or hold water; removing visible plants, animals and mud; and draining water from all compartments/containers. As indicated in the New York Watercraft Inspection Steward Program Handbook (New York Sea Grant 2014), watercraft inspection led by stewards is an effective way to:

  • Inform boaters about AIS issues and teach them how to intercept the potential introduction and establishment of AIS;
  • Help reduce the spread of AIS between waters; and
  • Empower boaters to protect the natural resources they love.

An example of an AIS watercraft education program include the Clean Boats Crew: Guidelines for the Illinois and Indiana Aquatic Invasive Species Volunteer Outreach Program manual, which provides information on how volunteers can organize an AIS watercraft education program, including how to conduct an inspection and a sample script for approaching recreational users.



Detection

New Populations: Early detection of new populations is critical to control the spread of hydrilla, as is monitoring of existing infested sites. Active and passive detection networks are necessary to survey and monitor high-priority waterbodies. Within these waterbodies, visual monitoring should prioritize boat ramps/launches and inlets without existing infestations. Additionally, popular recreational waterbodies and embayments with marinas, and waters less than 25 feet in depth should receive higher priority. Inland waterbodies are expected to be more vulnerable to a hydrilla infestation than the Great Lakes proper because they are less turbulent, shallower, and warmer. A specific, unified or universal process should be developed for people to report sightings/presence of hydrilla; this process should include agency verification of those reports. For example, the Hydrilla Hunt! program encourages the public to take and send close-up photos of aquatic plants that they suspect may be hydrilla, along with a description of where the plant was found, to an email address where the plant can be verified by an expert (Northeast Illinois Invasive Plant Partnership 2018).

Areas with Current Infestations: In areas with current infestations, monitoring efforts should focus on areas near these existing infestations. Use of a bathymetric map of the site can help to identify areas where water depths are suitable for hydrilla (i.e., 25 feet or less), and transects can be established in those areas at regular intervals. If resources are limited, transects should be prioritized based on likely invasion points (access points) or potentially threatened resources (e.g., intakes, swimming areas, and key habitat).



Response

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.