Mechanical/Physical Control Options
Eelgrass can be removed by cutting and raking it from the pond but can reestablish from remaining roots.
Fertilization to produce a phytoplankton or algal “bloom” prevents the establishment of most bottom rooted aquatic weeds and produces a strong food chain to the pond fish.
Non-toxic dyes or colorants prevent or reduce aquatic plant growth by limiting sunlight penetration, similar to fertilization. Aquashade, Blue Springs, and Crystal Blue are examples of non-toxic dye and other products are available. However, dyes do not enhance the natural food chain and may suppress the natural food chain of the pond.
Many types of mechanical removal devices are available that cut or chop up aquatic weeds. It is important to remember that many submerged plants regrow from fragments, so removal of cut fragments many be necessary to keep from spreading the unwanted plant. Companies that make cutters and rakes include but are not limited to Cutting Edge, Jenson Lake Mower, Midwest Aqua Care, and WeedRoller.
Physical barriers are also used to eliminate plants by shading the bottom. These work well for swimming areas, docks, etc. but must be kept clean of any buildup of sediment and debris. Lake Mat and Lake Bottom Blanket are examples of companies that makes these mats.
Biological Control Options
Grass carp will seldom control aquatic vegetation the first year they are stocked. They will consume eelgrass but it is not a preferred food item. Grass carp stocking rates to control eelgrass are usually in the range of 7 to 15 per surface acre. In Texas, only triploid grass carp are legal and a permit from the Texas Parks and Wildlife Department is required before they can be purchased from a certified dealer (list at the end of the packet).
Chemical Control Options
The active ingredients that have been somewhat successful in treating eelgrass include diquat (F) and endothall (F). F = fair
Reward is a liquid diquat formulation that has been somewhat effective on eelgrass. It is a contact herbicide. Contact herbicides act quickly and kill all plants cells that they contact.
Hydrothol 191 is an alkylamine salt of endothall and comes in both liquid and granular formulations. It is a contact herbicide and has been somewhat effective on eelgrass. Contact herbicides act quickly and kill all plants cells that they contact. Hydrothol can be toxic to fish.
One danger with any chemical control method is the chance of an oxygen depletion after the treatment caused by the decomposition of the dead plant material. Oxygen depletions can kill fish in the pond. If the pond is heavily infested with weeds it may be possible (depending on the herbicide chosen) to treat the pond in sections and let each section decompose for about two weeks before treating another section. Aeration, particularly at night, for several days after treatment may help control the oxygen depletion.
One common problem in using aquatic herbicides is determining area and/or volume of the pond or area to be treated. To assist you with these determinations see SRAC #103 Calculating Area and Volume of Ponds and Tanks.
Many aquatically registered herbicides have water use restrictions (See General Water Use Restrictions).
To see the labels for these products click on the name. Always read and follow all label directions. Check label for specific water use restrictions.
Eelgrass can be propagated by digging up whole plants and transplanting them into clear, shallow water.