Management Practices - Great Lakes Hydrilla Collaborative

Prevention

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

Develop a targeted educational campaign for angler groups focused on prevention, including the impacts of hydrilla on sport fishing and the need to be proactive in prevention (i.e., reporting hydrilla sightings).

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.

For coastal wetland restoration projects within the littoral zones of the Great Lakes, include specific requirements for pre-construction screening of fill material and post-construction monitoring of invasive species, including hydrilla, in project plans and specifications.

Early Detection

Train professionals to detect hydrilla early, especially in areas where there is heightened concern. Provide information on who to contact if hydrilla is found, or a plant is suspected to be hydrilla.

Develop a specific process for people to report sightings/presence of hydrilla, including agency verification.

Visual monitoring should prioritize prioritize (a) boat ramps/launches and inlets in waterbodies without existing infestations, (b) popular recreational waterbodies and embayments with marinas, and (c) waters with depths less than 25 feet.

Invasive species check station at Pymatuning State Park, Pennsylvania.

Focus monitoring efforts on areas near existing infestations, using a bathymetric map or transects prioritized by likely invasion points or potentially threatened resources.

Include signage at boat ramps to help aid early detection and provide outreach to lake associations, lake user groups, and marina owners. Signage should focus on how to report the presence of hydrilla or a plant suspected to be hydrilla.

Management

Timing of Herbicide Treatment

To maximize use of available management resources, conduct surveys for hydrilla when water temperatures reach 62.6 °F (17°C) for at least two weeks.

Conduct pre-treatment plant surveys beginning in mid-July to inform the annual treatment plan, as surveys will determine plant locations and provide input to determine duration and dosage of treatment.

Employ chemical treatment after tubers have sprouted (late June to July) but before the formation of new tubers (late August to November). In the Great Lakes Basin, time systemic chemical treatments, (e.g., use of fluridone, which targets vegetative tissues such as leaves, stems, and roots) to occur no earlier than mid-June, as systemic herbicides should be applied when tubers are sprouting.

Treatment: General

Use bathymetric data to accurately determine water volume. This will help in the development of treatment plans that will achieve more consistent and evenly distributed herbicide concentrations, which is more efficient and cost-effective.

Provide herbicide applicators with GIS shapefiles of treatment areas that can be downloaded into their GPS systems. Doing so will help to keep herbicide applications in the target area of interest.

Treatment: Rapid Response

Focus response efforts on use of a contact herbicide.

Advocate that state agencies develop a streamlined process that facilitates rapid response upon detection.

Treatment: Long-Term Control of Patches

Apply contact herbicides at the maximum label rates, along with limiting public access in treatment areas.

Use benthic mats (i.e., burlap barriers) on very small patches of hydrilla in shallow, low-velocity water.

Use limnocorrals (impermeable dividers) to isolate hydrilla beds for direct application of herbicide.

Limnocorral used near a marina on Tonawanda Creek.

Monitoring

Monitoring is critical to assess the rate of plant expansion, inform the components of a treatment plan, and evaluate the efficacy of a treatment plan. Monitoring is also critical to obtain an estimate of remaining hydrilla populations after each year of treatment. Monitoring data are also used to inform the development of annual treatment plans, including identification of treatment locations and the duration and dosages of herbicide treatments. Annual monitoring should include the following:

Resources for Tuber Sampling

• Monoecious Hydrilla Tuber Dynamics Following Various Management Regimes on Four North Carolina Reservoirs

• Lake Manitou Aquatic Vegetation Management Plan Update, Fulton County, IN

Hydrilla tuber.

• Assessment of tuber presence and density: Conduct annual fall tuber sampling at established locations via taking sediment cores, which provides an indication of tuber presence and density. Conduct this intensive monitoring for the first couple of years of a treatment plan because, as multi-year management projects progress, tuber numbers get so low that the sampling effort outweighs the benefits of collecting the data to demonstrate significantly reduced tuber values. During the later years of a project, perform assessments of plant species diversity and abundance as described below.

USACE Buffalo monitoring for hydrilla on Cayuga Lake.

• Assessment of plant species diversity and abundance: Annual rake-toss data provide an indication of hydrilla abundance (estimated biomass) as well as overall plant species diversity. Conduct surveys pre- and post-treatment each year using grids established using the point-intercept method. Pretreatment surveys should be performed in mid- to late July, and post-treatment surveys should be performed in late September through early November. If new locations of hydrilla are identified, increase the grid size to facilitate a larger search area for detection. Assess the rate of plant expansion to inform the control strategy. Record the following metrics: native and rare plant species presence and abundance; and hydrilla plant status, include whether plants are injured, and whether there is re-growth or formation of tubers or turions (i.e., a dormant bud produced by the above-sediment portion of the plant, capable of growing into a new plant when released from the parent plant).

¹Systemic herbicides are absorbed by vegetative tissues (foliage, roots) and translocated to other parts of the plant.