Plant control options
Users who want to control aquatic plants in the Three Lakes have a number of options, but the first step is to know your weeds. Among submersed plants, the biggest weed issue is often milfoil. Eurasian water milfoil (EWM) is an invasive plant that has spread widely throughout our lakes. While it can out-compete native vegetation, in our lakes native bassweed can generally hold its own against EWM and can grow in dense stands. We also find nuisance levels of native elodea and coontail. Our lakes also have some nuisance level patches of floating leaf plants: white water lilies and spatterdock. The recent reports on the plant survey page have plant photos and descriptions.
Plants are a part of the lake environment. As one lake scientist says, where light hits the bottom, plants will grow. Removal of most of the plants is will cause significant changes to the lake ecosystem. Wetland and aquatic plants provide many beneficial ecosystem services and some plants will always need to remain in our lakes to keep a natural, functioning lake environment.
Physical controls include hand harvesting, suction harvesting, mechanical harvesting, and benthic barriers. Chemical controls are herbicides. Biological controls include grass carp and weevils.
Hand harvesting. Recommended for our lakes: plants and fragments should be removed
Hand pulling is exactly what it sounds like: an individual pulls out plants. This is labor intensive, but can be successful in small areas, especially when pulling up plant roots. Harvested plants should be removed from the lake. Some report that significant harvesting may reduce regrowth in subsequent years. This option may not be viable in all areas because of bottom contour or plant density.
Suction harvesting. Recommended for our lakes: know your vendor
A snorkeler or scuba diver will pull out plants, and feed it to equipment that will collect the material. Suction dredging allows a high rate of plant removal since the diver does not have to carry pulled plants to a disposal point. This technique was used by Three Lakes Council as part of BEEP, the Brazilian Elodea Eradication Project: this project eradicated invasive Brazilian elodea from one cove of Lake Waccabuc in 2009. Other lakefront owners have also had some success with this approach. Anyone engaging a vendor to do suction harvesting should ensure that the materials removed from the lake are disposed of properly. Vendors must not dump plants on untended forested or common areas, and may charge more to remove plant material from the area.
Mechanical cutting and mowing: Hand cutting is ok, but larger equipment is not encouraged
Hand cutting is similar to hand harvesting and can be successful when attempts to remove fragments. Various cutters and rakes are commercially available. Use of large mechanical harvesters is not currently recommended. In mechanical harvesting, a blade or a larger mechanical device severs the top part of the plant from the remaining rooted portion. This is generally compared to mowing the grass, requires repetition throughout the season, and often can’t capture cut weeds. Mechanical harvesting is generally an expensive proposition because of the need for repeated treatments, needs care to capture and dispose of fragments, and can encourage subsequent denser plant growth at the surface.
Benthic barriers — Highly recommended: maintenance may be needed for long term success
Benthic barriers can be a highly effective plant control technique, especially for limited areas or to make a path to deeper water. Benthic barriers, also called bottom blankets, work by preventing light from reaching the plants on the bottom. These can be difficult to deploy, must be weighted down, and are most effective when put out before plants grow extensively in the spring. Benthic barriers can be successful against floating leaf as well as submersed plants. If left in place, over time they can become less effective when sediment is allowed to accumulate, as plants can then grow on top of the barrier. Some vendors install and then move benthic barriers annually, and other people have had success in removing sediment with a broom. The Two Lake Club has kept a benthic barrier in place next to a dock for years.
Chemical herbicides – not recommended for use in the Three Lakes
The principal reason against herbicide use in our lakes is that many residents obtain drinking and household water from the lakes. This makes getting a permit extremely difficult. In addition, herbicide use would disrupt the current ecological balance. While newer herbicides have improved selectivity, they still can be disruptive. Some of the lakes that use herbicides against plants see an increase in algal blooms. Some area lakes have an herbicide treatment for plants early in the year, and then have algaecide treatments every two weeks during the summer season. Repeated surveys of Three Lakes Council community residents show a preference not to consider herbicides as a weed management tool.
Grass carp – not currently recommended for the Three Lakes
Grass carp are selective eaters, and milfoil is their least preferred food. Grass carp may take several years to have an impact on plant life. Initially, milfoil may increase since carp eat the native plants first. As the carp grow, they eat more, and often completely eliminate plants in the lake. Significant algae blooms, especially cyanobacteria blooms, have occurred in lakes where grass carp have been introduced.
Milfoil weevils and moths — milfoil weevils and moths may help, but introductions have not been successful
Enough native weevils and naturalized aquatic moths occur naturally in some lakes to affect the amount of milfoil. Attempting to supplement lakes with weevils has had limited to no success. Reasons given for the lack of success include lack of reproductive success, fish predation, disruption by boats, and poor overwintering conditions. Few weevil vendors remain active.
Summary
No single plant control option is ideal in all locations or for all plants. Many of these plant management techniques have both advantages and disadvantages, and some require permits and careful oversight. Sources used for this include the highly recommended Chapter 6 of Diet for a Small Lake and The Practical Guide to Lake Management in Massachusetts. Many additional resources exist.