Fortunately, there are non-chemical methods available for management of invasive aquatic vegetation. Below is some basic information about several available methods, although often the best approach would be integrating the use of several of these methods to fit different areas of a lake.
For about the same price as most pesticide treatments, many commercial divers offer services for aquatic weed control. This simple process involves little more than sending divers down with mesh bags or vacuum hoses to remove weeds by hand and transport them to the surface for proper disposal. Not only does diver pulling preserve desirable native plants while targeting only invasive weeds, but it ensures that the entire invasive plant and root structure will be removed from the water to prevent rapid re-growth. Diver pulling is effective, environmentally safe, and unlike pesticides, subsequent dives should cost less than the initial treatment.
Bottom Barriers and Weed Rollers
Both of these products offer great weed control for swimming areas or space beneath docks.
Bottom barriers are little more than heavy, durable blankets designed to compress vegetation and block sunlight to prevent further growth. Placed directly on the bottom or mounted to a frame, bottom barriers (made of burlap, plastic, mylar, woven synthetics, or commercial materials designed for weed control) can be moved easily and provide 100% weed control wherever they are placed. If properly anchored and maintained, bottom barriers should not interfere with swimming, boating, or any other recreational activities. The cost is about $750 for 1,000 square feet of bottom screening.
Weed rollers also provide effective weed control for the area underneath a dock or swimming platform. A weed roller is a long pipe (up to 30 feet) with a low-voltage power unit which attaches to a dock or piling and sweeps back and forth over the bottom in an adjustable arc to keep weeds and vegetation clear. Once installed, the unit can be used as little as one day a week and draws little more power than a lightbulb. Like bottom barriers, weed rollers should not interfere with swimming or other activities and they require even less maintenance than bottom screens do. The initial cost of installation is about $2,000.
Mechanical harvesters are machines which can be used for clearing large, open spaces of water with weed infestations. Harvesters operate much like a giant lawnmower, cutting the weeds down to a depth of 5 or 10 feet and removing the waste material for disposal. Harvesters can cut an acre or two per day and provide immediate weed relief, although you will almost certainly need to harvest more than once during a season. Harvesting generally costs about $500 to $800 per acre, although it may cost less.
Hand Raking and Cutting
There are a number of different handheld rakes and cutters currently on the market which allow individual homeowners to control weeds in front of their houses and docks. Most of these control methods are simple and easy to use and generally cost around $100-$150. Weeds can be removed from the water, dried, and used as mulch or fertilizer. There are also smaller, home-use mechanized cutters that are available for purchase that cut vegetation at a depth of several feet below the water’s surface.
For more information on these non-chemical control methods and others, visit the Washington State Department of Ecology Aquatic Plant Management website.