Note: the following information was extracted from these sources:

Aquatic Ecosystem Restoration Foundation

http://www.aquatics.org/index.html

Washington Department of Ecology
http://www.ecy.wa.gov/programs/wq/plants/management/aqua028.html

All aquatic plant management techniques have positive and negative attributes.  None of the techniques is without some adverse environmental impact; all have both strengths and weaknesses.  In selecting management techniques, selections need to be based on economic, environmental, and technical constraints.

Mechanical Harvesters

Though we have only tried a harvester for one day in our project area, the use of mechanical harvesters and chopping machines needs to be carefully considered.  Resulting EWM plant fragments may easily re-grow or be carried downstream to create new infestations; harvesting machines are effective at reducing a large bio-mass in a short time, however, harvesting may have to be done several times per year.

Benthic Barriers

Description of Method
In addition to controlling nuisance weeds around docks and in swimming beaches, benthic barriers (also bottom barriers, bottom screening) has become an important tool to help eradicate and contain early infestations of noxious weeds such as Eurasian watermilfoil and Brazilian elodea.  Pioneering colonies that are too extensive to be hand pulled, can sometimes be covered with bottom screening material.

Our barriers are made of a 10 ft. X 10 ft. piece of spun, nylon fabric (versus woven), attached to a square frame made of Schedule 40 PVC pipe, one (1) inch in diameter.  Opposite ends of the fabric are attached with stainless-steel screws to two (2) straight, 10 ft. lengths of the PVC pipe (like a scroll), which are then filled with sand and plugged with foam.  PVC elbows (90°) are attached on each end of the two pipes, then two (2) more 10 ft. lengths of pipe are fitted into the elbows, completing the square frame.  Because the barrier can be dismantled and rolled up, it carries well on a boat or in a truck.  Divers, once the barrier is assembled, can float over the area of EWM infestation, then sink it into place.  When removing the barrier, it can be disassembled and rolled up, then transferred to a waiting vehicle or boat.  These barriers are non-reactive in the water and can be reused for another season if washed and stored dry.

The advantages of benthic barriers is:

• Installation creates an immediate open area of water with no vegetation.

• They are easily installed around docs and in swimming areas.

• Control of aquatic vegetation can be up to 100%.

• Installation can be done (with the proper permits) by a homeowner or diver.

The disadvantages of benthic barriers is:

• Because they reduce habitat by covering the sediment, they are suitable only for localized control.

• For safety and performance reasons, they must be regularly inspected and maintained.

• Harvesters, fishing gear, propeller backwash and boat anchors may damage, move or dislodge the barrier.

• If improperly weighted or anchored, they can create a safety hazard for boaters and swimmers.

• Some can move if not anchored into place on deep sediments.

• They could interfere with bottom-dwelling animals and fish spawning.

• If they are not maintained, sediment build-up will allow aquatic plants to colonize on top of the barrier.

In Idaho, barrier research during the 2005-2006 seasons in Lake Coeur d'Alene showed that between 8 and 10 weeks of  coverage was needed to be effective for EWM eradication.

Permits for benthic barriers in our area were provided by the Idaho Department of Lands - Coeur d'Alene Field Office, limited to placement and removal within the EWM growing season.

Costs for use of the barriers are based on barrier materials, placement and removal.  For our projects, benthic barrier costs $1.00 per square foot, so a standard 10 ft X 10 ft barrier placed and removed is $100.00.  A maintenance cost to clean the sediment off the barrier during the season varies by contractor.

Diver Hand-Pulling

Description of Method

Diver hand-pulling is an effective way of EWM removal in small areas or for widely scattered, single plants.  When treating EWM, light to medium infested areas within a small space can be easily removed and the control is complete.  The EWM is gently lifted from the bottom sediment, including the root system, and placed in a canvas or netted bag.  The diver must be careful to not damage the plants, causing fragments to form and float away.  Once the bag is full, the collected material is placed in totes on a diving platform and disposed of at the landfill.

The advantage of hand-pulling is:

• Small areas can be quickly cleaned.

• Plants are completely removed from the system.

• Areas not accessible by boat or incompatible to barrier placement can be accessed with a diver.

• No permits are necessary for the work.

The disadvantages of diver hand-pulling are:

• The activity is time consuming.

• Many divers are unfamiliar with identification of EWM.

• The high cost per hour or per day.

• Disposal of the bio-mass.

Diver hand-pulling costs include the diver(s) labor (no less than 2 divers for safety), air tanks and air refills or an air-assist pump, diving platform (boat or pontoon barge), fuel, bags and totes for disposal.  The average cost is $125 per hour for two (2) divers.

Diver Hand-Pulling/Suction Assisted

Description of Method

Diver hand-pulling with suction assistance (also know as diver dredging) is the same activity as above, only instead of placing the EWM plants in a bag, a vacuum pump and hose is utilized to suck the plants into a catch-cage (a screen box) located on the diving platform.  Typical pumps used for the operation are dredge or mining (reclamation) pumps, hooked up with a hose attached to a power jet (venture tube) that creates suction as air pressure pulls water through the hose.  Divers can "vacuum" a larger area than with hand-pulling alone, but the water can get murky with the movement of sediment where the EWM is being pulled.

The advantages and disadvantages are the same as hand-pulling.

Costs for diver hand-pulling with suction assistance are slightly higher than hand-pulling alone, due to the added expense of the pump system being part of the equipment necessary for the job.  The average cost is $240 per hour for two (2) divers.

Herbicides

Description of Method

Aquatic herbicides are chemicals which are specifically formulated for use in water to kill or control aquatic plants.  Herbicides approved for aquatic use by the United States Environmental Protection Agency (EPA) have been studied and tested and are considered compatible with the aquatic environment when used according to label directions.  Aquatic herbicides can be sprayed directly onto floating or emergent aquatic plants or applied to the water in either a liquid or pellet/granular form.  Liquid herbicides are generally injected below the water surface while the pellet/granular forms are spread across the water surface and allowed to sink.  Systemic herbicides are capable of killing the entire plant.  Contact herbicides cause the parts of the plant in contact with the herbicide to die back, leaving the roots alive and able to regrow.  Non-selective, or "broad spectrum" herbicides will generally affect all plants that they come in contact with.  Selective herbicides will affect only some plants.  Often dicots - broad leafed plants like Eurasian watermilfoil (Myriophyllum spicatum) - will be affected by selective herbicides whereas monocots like most native aquatic plants will not.

Because of environmental risks from improper application, aquatic herbicide application in Idaho waters is regulated and has the following restrictions:

• Applicators must be licensed by the Idaho Department of Agriculture.

• Notification to appropriate State or Tribal agencies is required before applications are made.

• Notification and posting are required and there may be additional mitigations proposed to protect rare plants or threatened and endangered species.

The chemicals that are currently permitted for use in controlling EWM in Idaho are:

• Fluridone – (Trade names for fluridone products include: Sonar® and Avast!®). Fluridone is a slow-acting systemic herbicide used to control Eurasian watermilfoil and other underwater plants. It may be applied as a pellet or as a liquid. Fluridone can show good control of submersed plants where there is little water movement and an extended time for the treatment. Its use is most applicable to whole-lake or isolated bay treatments where dilution can be minimized. Fluridone is generally not effective for spot treatments of areas less than five acres. It is slow-acting and may take six to twelve weeks before the dying plants fall to the sediment and decompose. When used to manage Eurasian watermilfoil, fluridone is applied several times during the spring/summer to maintain a low, but consistent concentration in the water. Some new granular formulations of fluridone are proving to be effective when treating areas of higher water exchange. Although fluridone is considered to be a broad spectrum herbicide, when used at very low concentrations, it can be used to selectively remove Eurasian watermilfoil. Some native aquatic plants, especially pondweeds, are minimally affected by low concentrations of fluridone.  (Click here to read product label for Sonar AS liquid)  (Click here to read product label for Sonar PR pellet)
   

• 2,4-D – There are two formulations of 2,4-D approved for aquatic use. The granular formulation contains the low-volatile butoxy-ethyl-ester formulation of 2,4-D (Trade names include: AquaKleen® and Navigate®). The liquid formulation contains the dimethylamine salt of 2,4-D (Trade name - DMA*4IVM). 2,4-D is a relatively fast-acting, systemic, selective herbicide used for the control of Eurasian watermilfoil and other broad-leaved species. Both the granular and liquid formulations can be effective for spot treatment of Eurasian watermilfoil. 2,4-D has been shown to be selective to Eurasian watermilfoil when used at the labeled rate, leaving native aquatic species relatively unaffected. (Click here to read Washington’s 2,4-D risk assessment) (Click here to read product label for DMA 4 IVM) (Click here to read product label for Navigate).
   

• Triclopyr - (Trade name Renovate3®). There are two formulations of triclopyr. It is the TEA formation of triclopyr that is registered for use in aquatic or riparian environments. Triclopyr, applied as a liquid, is a relatively fast-acting, systemic, selective herbicide used for the control of Eurasian watermilfoil and other broad-leaved species such as purple loosestrife. Triclopyr can be effective for spot treatment of Eurasian watermilfoil and is relatively selective to Eurasian watermilfoil when used at the labeled rate. Many native aquatic species are unaffected by triclopyr. (Click here to read Washington's Environmental Impact Statement for triclopyr)  (Click here to read product label for Renovate 3 liquid) (Click here to read product label for Renovate OTF flake).
   

• Endothall  – (Trade name Aquathol®) Endothall, the dipotassium salt, is a fast-acting non-selective contact herbicide which destroys the vegetative part of the plant but generally does not kill the roots. Endothall may be applied in a granular or liquid form. Typically endothall compounds are used primarily for short term (one season) control of a variety of aquatic plants. However, there has been some recent research that indicates that when used in low concentrations, endothall can be used to selectively remove exotic weeds; leaving some native species unaffected. Because it is fast acting, endothall can be used to treat smaller areas effectively. Endothall is not effective in controlling Canadian waterweed (Elodea canadensis) or Brazilian elodea. (Click here to read Washington’s risk assessment for endothall) (Click here to read product label for Aquathol K liquid) (Click here to read product label for Aquathol Super K granular). 
   

• Diquat – (Trade name Reward®). Diquat is a fast-acting non-selective contact herbicide which destroys the vegetative part of the plant but does not kill the roots. It is applied as a liquid. Typically diquat is used primarily for short term (one season) control of a variety of submersed aquatic plants. It is very fast-acting and is suitable for spot treatment. However, turbid water or dense algal blooms can interfere with its effectiveness. (Click here to read Washington’s risk assessment for Diquat) (Click here to read product label for Reward).