One possible solution to isolated vegetation problems is to use a dense fabric or black plastic to shade aquatic plants from sunlight. Black plastic sheeting or a dense weave geo-textile can be attached to floats to keep it on the water surface where it can serve as a floating shade. The shade can be floated easily from one place to another for spot treatment of nuisance water plants in small areas.
When using a physical light barrier to control aquatic vegetation, the treatment must remain in place for 30 days to be effective. Use of a physical barrier is best suited for small, controlled areas such as around boat docks, fishing piers, and swimming beaches. These barriers can present problems with access to the treatment area, dislocation by wave or wake actions and difficulty keeping the barrier anchored in place.
UV Light Inhibitors
In some areas, pond owners have used UV light inhibitors which are harmless dyes. When mixed with the pond water, the products produce a dark color which reduces the ability of light to penetrate the water column. Reducing the light penetration in the pond inhibits the growth of submergent vegetation. Commercially available nontoxic water dyes (nigrosine™, analine™, and aqua-shade™) can be used to color the water in order to reduce light penetration and shade out nuisance plants.
To be effective, the dyes must persist for several weeks and in ponds with frequent changes in the water's volume (i.e. the pond is located on a flowing stream or waterway) this may be a costly strategy. For the best results, this technique should be used in early spring at the start of the growing season before the water-weeds have had a chance to establish themselves.
In New York State, chemical dye compounds for aquatic weed applications are considered registered substances and their use requires a permit from New York State Department of Environmental Conservation. For landowner use of these chemicals, a licensed pesticide applicator is not required, but the landowner must obtain a permit for purchase of the chemicals from a registered dealer. You may contact NYSDEC for these permits at the following link: NYSDEC Aquatic Weed Control Permits Home Page.