AQUATIC PLANT CONTROL ALTERNATIVESBrazilian Elodea

Lake Leland Integrated Aquatic Plant Management Plan

 


Treatment methods for the control of noxious aquatic plants are various (physical, mechanical, biological, chemical) and may be initiated for the short term or long term. What works in one situation may not work in another. Or perhaps a combination of treatments might be best. The steering committee examined each available option in terms of suitability for Lake Leland. Environmental effects, costs, user friendliness, effectiveness, and permitting were points for evaluation. Management of Lake Leland as a whole with its variety of uses (wildlife habitat, excellent fishery, domestic water source, recreation) was taken into account. Both the advantages and disadvantages of each control method were considered.

The following descriptions were excerpted from A Citizen’s Manual for Developing Integrated Aquatic Vegetation Management Plans (Gibbons et al. 1994) and Aquatic Plants and Fish (WDFW 1998b). Additional information was gathered from presentations by Kathy Hamel (Ecology), Scott Bonar (WDFW), and Dan Collins (WDFW).

The following is a list of control alternatives as presented to the steering committee by Kathy Hamel. Those controls most pertinent to Lake Leland or Leland Creek are in bold.

Physical Controls

  • Hand-pulling / cutting
  • Bottom barrier
  • Water level drawdown

Mechanical Controls

  • Harvesting and cutting
  • Rotovation
  • Diver-operated dredging

Biological Controls

  • Triploid grass carp

Chemical Controls

  • Fluridone
  • Glyphosate
  • Endothall

No Action Alternative

PHYSICAL CONTROLS

HAND-PULLING

Description Hand-digging and removal of rooted, submerged plants is a labor intensive control method. This method involves digging out the entire plant with roots. Plants are then deposited in a dry disposal area away from the shoreline. No specialized gear is required in waters less than three feet. In deeper waters, hand pulling is most efficient with divers using snorkeling equipment or SCUBA gear. Divers carry mesh bags for collection of plants. Plants then need to be disposed of on shore.

Effectiveness and Duration Sediment type, visibility, and thoroughness in removal of the entire plant, particularly the roots, all affect the speed at which plants are removed. A high degree of control, lasting more than one season, is possible when complete removal has been achieved.

Advantages This method results in immediate clearing of the water column of nuisance plants. The technique is very selective in that individual plants are removed. It is most useful in sensitive areas where disruption must be kept to a minimum and also works well in hard to get places. It is a highly labor intensive control and, therefore, most appropriate in small or low density areas. Environmental impacts, including turbidity increases and bottom disruption, are short-term.

Disadvantages This method is time-consuming and can be very costly if contract divers are employed. Diver visibility may become obscured by the digging process, making it difficult to see and remove roots. Hand-pulling is not practical for large areas.

Costs Costs will vary depending on whether contract divers and laborers or volunteers are used. According to the 1994 IAVMP Manual, expenses can run between $500 to $2400 per day.

Permits Hydrologic Project Approval (HPA) is required from Washington Department of Fish and Wildlife at no charge. The process includes requesting and reading a pamphlet titled Aquatic Plants and Fish (WDFW 1998b). The booklet itself serves as the HPA and is available from WDFW area habitat biologist Chris Byrnes, Port Orchard, WA, 360-895-6123.

Appropriateness for Lake Leland This method would be useful for small-area, short-term control of Brazilian elodea around private docks and along short shoreline segments. Some type of boom or boat could be used to help collect fragments. Hand-pulling or digging is also suggested as a control method for the removal of yellow flag iris, although residents who have tried this report that it is very labor intensive.

HAND-CUTTING

Description This is also a manual method but does not involve hand-pulling the roots. The plants are cut or torn using tools that can be pulled through the weed beds by boat or manually. This work can be done using hand held cutting tools, some of which may be powered. Items such as rakes, chains, logs, railroad ties, or even old bedsprings may be dragged across the bottom to collect plants. Collected plants should be disposed of at a dry land location. Because roots are not removed, this is a less intensive removal technique. Mechanized weed cutters are also available that can be operated from the surface for small-scale control (similar to an underwater lawnmower). And mechanized weed rollers, which flatten and wear down weeds by frequent agitation, are useful around docks. Weed rollers can be shared by neighbors but are cumbersome to install.

Effectiveness and Duration With hand-cutting, root systems and lower stems are left intact. As a result, effectiveness is usually short-term as rapid regrowth is possible from the remaining root masses. Duration of control is limited to the time it takes the plant to grow to the surface (probably less than one season). With a weed roller, control is achieved on a continuos basis.

Advantages Hand-cutting and mechanized weed cutters or rollers result in immediate removal of the nuisance plant and quickly create open water for swimming or fishing. Hand-cutting is similar to hand-pulling but costs can be minimal. Hand-cutting is site specific and can be species specific, if care is used, which minimizes environmental disruption. Mechanized rollers and cutters are site specific and offer low-cost operation after the initial purchase.

Disadvantages The hand-cutting method is time-consuming and labor intensive. Visibility may become obscured by turbidity generated during cutting activities. This technique does not result in long-term reductions in growth because roots are left intact. Duration of control of Brazilian elodea would be minimal, probably less than one season. Cut plants must be removed from the water. Fragments are numerous, making clean up messy and laborious. This method is not practical for large areas. Mechanized weed rollers and cutters are expensive to purchase and require maintenance and are not species specific. Weed rollers are not permitted for removal of early infestations of noxious aquatic weeds because they create fragments and might help spread the plant to new locations.

Costs Assuming volunteers are used, costs are limited to the purchase of cutting implements. This can vary from under $100 for the Aqua Weed Cutter (Sunrise Corp.) to approximately $1500 for the mechanized underwater lawnmower Swordfish (Redwing Products). A Water Weed Cutter (Aquacide Company) was purchased for $135 and found to be a very effective tool.

Permits The permitting process is the same as for hand-pulling.

Appropriateness for Lake Leland Hand cutting of Brazilian elodea would be most applicable for short-term and small-scale control around private docks and in light areas of infestation along the shoreline. A hand-cutting tool called the Water Weed Cutter was demonstrated during the tool effectiveness workshop. It was used to clear a heavily infested area around a dock and was found quite easy to use. The actual weed cutting with the tool went rather quickly. The time consuming element was the collection of the weed fragments. One should note that though the tool is easy to use it is quite sharp and could be dangerous if safety is not kept in mind. In order to keep a dock weed-free with this cutter, one would probably need to use it several times a season. The mechanized weed roller may be used around private docks, but the area needs to be free of obstructions.

BOTTOM BARRIER

Description Barrier material is applied over the lake bottom to prevent plants from growing. Bottom covering materials such as sand-gravel, polyethylene, polypropylene, synthetic rubber, burlap, fiberglass screens, woven polyester, and nylon film have all been used with varying degrees of success. Typically, synthetic (geo-textile) fabrics or burlap are used. Bottom barriers can be used at any depth, with divers often utilized for deeper water treatments. Usually, bottom conditions (presence of rocks or debris) do not impede barrier applications, although pre-treatment clearing of the site is often useful.

Effectiveness and Duration Bottom barriers create an immediate open water area. Duration of control is dependent on a variety of factors, including type of material used, application techniques, and sediment composition. Synthetic materials like Aquascreen and Texel have eliminated nuisance plant conditions for at least the season of application. If short-term control is desired for the least expense, burlap is a good choice of materials. It has been known to provide up to two to three years of relief from problematic growth before eventually decomposing (Truelson 1989). The intensity of control is high. In some situations, after satisfactory control has been achieved (usually several months), bottom barriers may be relocated to other areas to increase benefits.

Advantages Bottom barriers can usually be easily applied to small, confined areas such as around docks, boat launches, or swimming beaches. They can be installed by homeowners. Bottom barriers are hidden from view and do not interfere with shoreline use. They are site specific and can be installed around obstructions. Bottom barriers do not result in significant production of plant fragments (advantageous for Brazilian elodea treatment). Barriers are most appropriately used for localized, small-scale control where exclusion of all plants is desirable.

Disadvantages Depending on the material, major drawbacks to the application of bottom barriers include some or all of the following: control not species specific, high material cost if used on a large scale, labor-intensive installation, limited material durability, possible suspension due to water movement or gas accumulation beneath material, eventual regrowth of plants from above material, requires area free of large obstructions. Periodic maintenance (yearly) of bottom barrier materials is beneficial to remove accumulations of silt and any rooting fragments. In some situations, removal and relocation of barriers may not be possible (natural fiber burlap decomposes over time). If used over a large area, sediment covers can produce environmental impacts such as a decrease in the populations of bottom-dwelling organisms like aquatic insects.

Costs Bottom barrier material costs vary depending on the type of material used. Rolls of synthetic material for aquatic barrier use can be purchased in 300 foot lengths and either 12 or 15 foot widths for $300 to $350. Rolled burlap material (available in fabric stores or outlets) averages from $0.15 to $0.25 / sq. ft. Costs for professional installation are an additional $0.25-$0.50 / sq. ft. A Leland community member has installed a bottom barrier using a 20 X 20 ft plastic tarp. These are relatively inexpensive to purchase at a local hardware store. Current costs are about $8.50 for an 8 x 10 ft tarp and $25 for a 16 x 20 ft tarp.

Permits The permit process is the same as for hand-pulling but prior authorization from WDFW is required for projects that exceed specified thresholds. See Aquatic Plants and Fish (WDFW 1998b) for specific information.

Appropriateness for Lake Leland Bottom barriers would be appropriate around docks at Lake Leland where there are no large obstructions and also along short stretches of shoreline. Cost and maintenance of bottom barriers confine them to very small-scale use. One barrier is currently being tested in front of a dock in the heavily infested south end of the lake. This barrier was cheaply constructed with a 20 X 20 ft plastic tarp which was tied to a frame of plastic pipe. Rebar was inserted in the pipe to weight it down. Sandbags or other weights could also be used. Ecology Publications offers a fact sheet on building bottom barriers (Appendix E). This and other publications may be obtained at no cost by calling Jean Witt, Ecology Publications at 306-407-7472.

WATER LEVEL DRAWDOWN

Description Drawdown involves exposing plants and root systems to prolonged freezing and loss of water. It is generally performed in winter months. The use of drawdown as an aquatic plant management tool is more common for use in reservoirs and ponds than in natural lakes. A water control structure for drainage or high capacity pumps are needed to draw the water down.

Effectiveness and Duration Although freezing can have a dramatic impact on some plants, Brazilian elodea is known to have over-winter buds. Also, temperatures in the Leland area rarely reach the sub-zero temperatures that would be necessary for a large scale kill.

Appropriateness for Lake Leland Drawdown is not feasible at Lake Leland. Because of this, advantages, disadvantages, costs, and permits relating to drawdown were not addressed.

MECHANICAL CONTROLS

HARVESTING / CUTTING

Description Mechanical harvesters are large floating machines that cut plants below the water surface. Harvesting is considered a short-term technique that temporarily removes nuisance plants. To achieve maximum removal of plant material, harvesting is usually performed during summer when submersed and floating-leafed plants have grown to the water’s surface. Conventional single-staged harvesters combine cutting, collecting, storing, and transporting vegetation into one piece of machinery. Cutting machines are also available which perform only the cutting function. Maximum cutting depths for harvesters and cutting machines range from 5 to 8 feet with a swath width of 6.5 to 12 feet.

Effectiveness and Duration The immediate effectiveness of harvesting is creating open water. The duration of control is variable. Factors such as frequency and timing of harvest, water depth, and depth of cut may influence the duration of control. Harvesting has not proven to be an effective means of sustaining long-term reductions in the growth of milfoil. Regrowth of milfoil to pre-harvest levels typically occurs within 30-60 days (Perkins and Sytsma 1987) depending on water depth and the depth of cut. Aquatic plant researchers note that any effects on the control of Brazilian elodea would also be short term.

Advantages Harvesting is most suitable for large lakes and open areas with few surface obstructions. A specific location can be targeted leaving an area open for fish and wildlife. There is usually little interference with recreational use of the water body during harvesting operations. By cutting only the top 5 ft of the plant, some habitat remains. Harvesting has the added benefit that removal of in-lake plant biomass also eliminates a source of nutrients, often released during fall die back and decay. This is of important consequence in those water bodies with extensive plant beds and low nutrient inputs from outside sources. Furthermore, harvesting can reduce sediment accumulation by removing organic matter that normally decays and adds to the bottom sediments. Depending on species content, harvested vegetation can be easily composted and used as a soil enhancement.

Disadvantages Cut plant material requires collection and removal from the water with off-loading sites needed for plant disposal. Collecting machines fill up very quickly which makes the process quite lengthy. Harvesting creates numerous plant fragments which would contribute to the spread of Brazilian elodea. It is not species specific and can be detrimental to juvenile fish which are removed indiscriminately by the process. Harvesting can enhance the growth of opportunistic plant species that invade treated areas. Capital costs for the machine purchase are high ($35,000-$150,000) and equipment requires considerable maintenance. Harvesters are not very efficient and repeated treatments are necessary--rather like mowing a lawn.

Costs Harvesting costs depend on a variety of factors such as program scale, composition and density of vegetation, equipment used, skill of personnel, and site-specific constraints. Detailed costs are not uniformly reported, so comparing project costs of one program to another can be difficult. Currently, contract aquatic plant harvesting operations cost about $750.00 per acre on non-prevailing wage rate projects and $1000.00 per hour if prevailing wage is required (McNabb pers. comm. 1998). Using a recent estimate of control at one acre per day, contracting would be very costly. The current purchase price for a new harvesting system is approximately $110,000 plus an ongoing operations and maintenance expense each year.

Permits The permit process is the same as for hand-pulling.

Appropriateness for Lake Leland Mechanical harvesting is more appropriate for larger lakes. The cost of the equipment would be prohibitive, particularly in the light of the short-term control offered by harvesting. Harvesting results in the production of numerous plant fragments which would contribute to a larger scale infestation of Brazilian elodea in the main lake.

ROTOVATION

Description Rotovation is basically underwater cultivation or rototilling using a barge-mounted rototiller or amphibious tractor towing a cultivator. Plants and root crowns are uprooted as bottom sediments are tilled to a depth of up to 12 inches. Bottom tillage is usually performed in the cold months of winter and spring to reduce plant regrowth potential. This technique is generally used for milfoil control and is most suitable for use in larger lakes due to the size of the equipment and the high cost.

Effectiveness and Duration Depending on plant density, control offered by rotovation may last up to two or three years.

Advantages A high percentage of entire plants, including the roots, can be removed during tillage. Plant density is generally reduced. By removing the canopy, tilling stimulates the growth of native plants which is of potential benefit to fish.

Disadvantages Bottom obstructions limit the use of rotovation. Tillage should not occur where water intakes are located. Short term turbidity increases in the area of operation, and short-term impacts on water quality and the benthic invertebrate community can occur (Gibbons et al. 1987). Rotovation is not advised where bottom sediments have excessive nutrients and/or metals because of their potential release into the water column. Rotovation is not species selective. Plant fragments are produced and the machine does not collect plants. The process is very labor intensive and expensive.

Costs Bottom tillage costs vary according to treatment scale, density of plants, machinery used and other site constraints. Contract costs for rotovation in Washington range from $1200-$1700 / acre depending on treatment size.

Permits An individual HPA is required from WDFW for all rotovation projects. Also, the use of bottom tillage requires a temporary modification of water quality standards from Ecology. A shoreline permit may also be required, so contact must be made with the Jefferson County Planning Department. It may also be necessary to obtain a letter of approval from Washington Department of Natural Resources.

Appropriateness for Lake Leland Rotovation is generally used for milfoil control and, like harvesting, is more suitable in a larger lake. This procedure is cost prohibitive and also would contribute to the spread of Brazilian elodea.

DIVER-OPERATED SUCTION DREDGING

Description With this technique, divers operate portable dredges with suction heads that remove plants and roots from the sediment--essentially vacuuming the bottom of the lake. The suction hoses draw the plant/sediment slurry up to a small barge or boat carrying the dredge. On the barge, plant parts are separated from the sediment slurry and retained for later off-site disposal. The sediment slurry can be returned to the water column.

Effectiveness and Duration Diver dredging can be highly effective under appropriate conditions. Removal efficiency depends on sediment condition, density of aquatic plants, and underwater visibility (Cooke et al. 1993). This technique works well to control early low-level infestations of milfoil or Brazilian elodea. It can also be used as a maintenance tool following herbicide treatments.

Advantages This method of control is site and species specific. Disruption of sediments are minimized. Plant parts are collected for later disposal, and the spread of fragments is minimized which is important in the control of Brazilian elodea or milfoil. Diver dredging can cover a much larger area than is practical for hand pulling and it can be effective in soft sediments. Also, it can be easily operated around obstacles and in tight places.

Disadvantages Diver dredging is labor intensive and very costly. Two divers and a tender are needed. Turbidity, and release of nutrients and other contaminants from disturbed sediments are some environmental concerns. The turbidity caused by the machine creates poor visibility which slows the process. Some sediment and non- target vegetation may inadvertently be removed during the process. Some fragment loss may be expected if dredged slurry is directly returned to the lake. It would be even more costly if slurry were disposed of upland.

Costs The costs can vary depending on density of plants, type of equipment used, and disposal requirements. State regulations on contract divers for dredging work are stringent and prevailing wage rates are high. Two divers and a tender are needed. Costs can range from a minimum of $1100 / day to upwards of $2000 / day with actual removal rates varying from approximately to one acre per day.

Permits Four different permits are needed, one of which takes up to two years. WDFW requires a Hydraulic Permit and the Corps of Engineers may also require a permit. A shoreline management permit is required from the Jefferson County Planning Department, and it may be necessary to obtain a letter of approval from DNR. A temporary modification of water quality standards due to increased turbidity is required from Ecology.

Appropriateness for Lake Leland This method is very costly, very labor intensive and slow going, so it isn’t very practical for widespread infestations such as in Lake Leland. It may work well at Lake Leland (with soft sediments) if volunteer equipment and labor were used, but, as mentioned above, the permitting process is long and can take up to two years. Some community members have discussed the possibility of building the equipment on a very low budget. If so, diver dredging could come up at a later date as a control of interest in selected areas.

BIOLOGICAL CONTROLS

The desire to find a more "natural" means for long term control, to reduce use of expensive equipment, and to eliminate the use of chemicals has created an interest in biological control agents to reduce the quantity of non-native aquatic weeds. The only biological method of control for Brazilian elodea at this time is the use of triploid grass carp. Grass carp were brought into the United States from Malaysia in the 1960’s and have been used to control aquatic weeds extensively in the South. Triploid carp, which are sterile, were legalized for use (by permit) in lakes and ponds in Washington State in 1990.

TRIPLOID GRASS CARP

Description Grass carp or white amur (Ctenopharyngodon idella) are plant consuming fish native to the large rivers of China and Siberia. They have definite feeding preferences, though there is a wide range of plants that they will eat. Under the right circumstances, these fish are known to control certain submersed nuisance aquatic plants. They are most suitable for use as a lake-wide, low intensity control over the long term.

Calculating the optimum stocking rate to achieve the desired control of the target plant is not easily achieved. Variable factors such as the amount of plant material available (both target species and other plants), water temperature, climate, and predators, along with past experiences from other lakes, are considered in determining the stocking rate. In order to introduce the carp, a permit is required from Washington Department of Fish and Wildlife (WDFW 1998b) and specific state regulations must be adhered to. Only sterile fish can be planted. Inlets and outlets must be screened to keep the carp out of other water bodies. These regulations are in place to prevent problems that have occurred in other lakes where grass carp were introduced.

In a study of 98 lakes in Washington State, Bonar et al. (1996) reported that grass carp achieved successful vegetative control in only 20 percent of the lakes. In 40 percent of the lakes, the grass carp denuded all the vegetation and in the remaining 40 percent no difference was noticed. Despite this low success rate, 83 percent of the landowners interviewed were satisfied with the results. It should be noted that in this study only lakes achieving over 50 percent of vegetative control were counted as successful. Also, most of the lakes were less than ten acres in size.

Control Effectiveness and Duration Effectiveness of grass carp in controlling aquatic weeds is dependent on several factors: feeding preferences, metabolism, temperature, and stocking rate (Ecology 1992). Grass carp eat in a hierarchy with distinct preferences. For example, newly introduced carp in Devil’s Lake, Oregon initially preferred thinleaf pondweeds (Potamogeton spp.). However, as the fish grew larger (12-14 inches), Brazilian elodea became the favored food. This change in food preference took approximately one year. According to WDFW biologist Scott Bonar (pers. comm. 1998), it generally takes about two to three years to see noticeable results from stocking when the density of carp is adequate. Restocking may be necessary in five to ten years.

Advantages Depending on the problem plant species and other site constraints, proper use of grass carp can achieve long-term reductions in nuisance growth of vegetation without much management. In some cases, introduction of grass carp may result in improved water quality conditions, where water quality deterioration is equated with dense aquatic plant growth (Thomas et al. 1990). Compared to other plant control techniques, costs for grass carp are relatively low though screens on inlets and outlets can add considerably to costs. Long term operation and maintenance costs are relatively inexpensive.

Disadvantages The target plant may not be high on the grass carp’s preference list. The fish may avoid areas of the water body experiencing heavy recreational use, resulting in less plant removal in these locations. Plant reductions may not become evident for several years. Full ecological impacts of grass carp introductions in Northwest waters are still being determined, and there may be a problem which is presently unrecognized.

Overstocking of grass carp could result in eradication of beneficial plants and have serious impacts on the overall ecology of the water body. Overstocked carp are very difficult to remove, and these fish can live 14 years or more in Washington waters. Also, costs for screening inlets and outlets can be substantial. Because of the unpredictability of grass carp control, the WDFW recommends that they not be introduced where total plant eradication and increased turbidity cannot be tolerated. Total eradication has caused turbidity problems in other lakes where all submersed plants were eaten and carp began rooting on the bottom. Other consequences of total submersed plant eradication include: loss of habitat which provides protection for young fish and other aquatic organisms, loss of a waterfowl food source, and the possible establishment of another invasive species in the newly created niche. With the removal of a large biomass of aquatic macrophytes, there is a potential for increased algae production.

Costs The costs for grass carp control include those for the fish and any needed screens for inlets and outlets. Rotating drum screens require electricity to run them. At a stocking rate of 10 to 25 fish per vegetated acre at an average cost of $10 per fish and an estimated 5 to 10 acres of Brazilian elodea, the fish cost would range from $500 to $2500. WDFW estimated a cost of $39,300 to install a drum screen at the existing fish weir on Leland Creek. This cost may be reduced with the use of volunteer labor. An additional screen on the major inlet may also be required.

Permits WDFW requires a game fish planting permit prior to grass carp introduction to a water body. In addition, if outlet screening is necessary, hydraulic approval is required from the WDFW. A shoreline exemption permit is required from Jefferson County Permit Center for "installation of a permanent or temporary structure within or near the lake" (Mark pers. comm. 1998). Department of Natural Resources Natural Heritage Program must be contacted for assessment of threatened or endangered plant species.

Appropriateness for Lake Leland Since Brazilian elodea appears to be a preferred food for grass carp, their use as a large-scale control in Lake Leland does have some merit. There has been quite a bit of discussion in the community about the use of carp, as it is a more preferred option than the use of herbicides. However, questions have been raised over the suitability of introducing one exotic species to control another exotic species. Because Lake Leland has an excellent fishery and supports a great deal of waterfowl and wildlife, the possibility of total vegetative eradication is a big concern. The habitat provides protection for young fish and other aquatic organisms and food for waterfowl. Wintering trumpeter swans feed on the Brazilian elodea but they have been seen on the lake long before the presence of the Brazilian elodea. Last year the swans spent a lot of time around the Leland Creek wetlands rather than on the lake.

To lessen the chance of total eradication, a conservatively low stocking rate could be used. A low stocking rate would also lessen the chance for increasing nuisance algae production. Even if the reduction of Brazilian elodea was less than 50 percent (the criteria used to determine success by Bonar et al. 1996), Leland residents would consider it successful. Besides stocking fewer carp, it could be advantageous to stock larger carp. Larger fish are less susceptible to predation and have a higher preference for Brazilian elodea than smaller fish.

At the present time, the steering committee does not endorse the use of grass carp but does not rule them out as a future option. The committee will periodically reassess conditions in the lake and reevaluate grass carp as a possible control. The committee will keep informed of the results of using grass carp in other lakes, especially Duck Lake (located on the Washington coast) where grass carp were stocked at a low density to control Brazilian elodea.

CHEMICAL CONTROLS

The use of aquatic herbicides has historically been a common method of controlling invasive aquatic weeds. In recent years, there has been a shift away from broad use of herbicides. Environmental, economic, political, and social implications are considered as well as results from thorough reviews of target effectiveness.

Currently, there are four aquatic herbicides allowed in the State of Washington for control of aquatic weeds. Two are the systemic herbicides fluridone and glyphosate. These herbicides are absorbed by the plant and can kill the entire plant roots and shoots. The third herbicide is endothall, a contact herbicide. This type of herbicide kills only the plant part that it comes in contact with leaving roots alive and capable of regrowth. A fourth herbicide is copper sulfate and chelated coppers. Copper compounds are generally only permitted for algae control at this time. Because copper accumulates in the sediment and never breaks down and can be toxic to fish, the state strongly discourages its use—even for algae management. Therefore, only fluridone, glyphosate, and endothall will be examined here.

FLURIDONE

Description More commonly known as SONAR, this herbicide is a very slow acting systemic type of herbicide that has to remain in contact with the plant for up to eight to ten weeks. It is commonly used in the management of aquatic plants in freshwater ponds, lakes, reservoirs, or irrigation canals. It is formulated as a liquid (SONAR 4AS) sprayed above or below the surface, and in controlled release pellets(SONAR SRP) which are spread on the surface of the water. Fluridone is effectively absorbed and translocated by both plant roots and shoots (Westerdahl and Getsinger 1988).

Effectiveness and Duration This chemical is most effective where there is little water movement and provides good control of both submersed and emergent aquatic plants in this situation. Its use is most applicable for whole lake or isolated bay treatments to control a variety of exotic and native species. Fluridone is reportedly successful in control of Eurasian milfoil and Brazilian elodea. Characteristics typical of fluridone use are whitened leaves, retarded growth, and plant mortality. Effects of fluridone treatment are noticeable 7-10 days after application with control of target plants often taking 60-90 days to become evident (Westerdahl and Getsinger 1988). Because of the delayed nature of toxicity, the herbicide is best applied during the early growth phase of the target plant, usually spring or early summer.

Advantages Because of its ability to kill roots and shoots, fluridone has a long lasting effect. A variety or emergent and submersed aquatic plants are susceptible to fluridone treatment. Extensive human health risk studies report that when used according to label instructions, fluridone does not affect human health. The chemical also has low toxicity to zooplankton, benthic invertebrates, fish, and wildlife.

Disadvantages Because of its slow acting capabilities, the effects of fluridone may take up to several months. It is not effective in flowing water situations because of the long uptake time needed for absorption and herbicidal activity. Fluridone is not suitable for treating a defined area within a large lake because of the potential for drift. Also the potential exists for release of nutrients to the water column and consumption of dissolved oxygen from the decaying plants. Non-target plants will be affected, because, as mentioned above, a variety of plants show degrees of susceptibility to fluridone treatment. Mitigation of lost vegetation may be necessary. There are label recommendations for delay in the use of treated waters for irrigation purposes. To protect drinking water sources, it is recommended that no applications be made within a quarter mile of a domestic water intake—although whole lake applications at 20 ppb or less target concentration can be made within a quarter mile of drinking water intakes (Hamel pers. comm. 1998).

Costs Sonar is an expensive herbicide. Treatment costs by private contractors vary depending on lake characteristics but start around $1000 per acre. A recent price quote recommended a budget of $116,000 for Sonar treatment of Lake Leland (McNabb pers. comm. 1998). This would include five Sonar treatments and five samplings, permitting, public notification, bathymetric mapping, and volume calculations. This price could be reduced, depending on how well the lake retains Sonar.

Permits The use of aquatic herbicides is regulated primarily by Ecology and Washington Department of Agriculture. Each agency should be contacted for recent information. A short-term modification to state water quality standards is required from Ecology prior to treatment. Jefferson County regulations require a shoreline exemption permit (Mark pers. comm. 1998).

Appropriateness for Lake Leland After discussions of the pros and cons of broad chemical use in the lake, the Leland community has chosen to look for alternative control options. This conclusion is based on environmental and human health concerns. The long term health effects for humans and wildlife are questioned. Untargeted native vegetation is killed. And, as mentioned earlier, there are lake residents who are dependent on the lake as a source of domestic water. Sonar label restrictions specifically refer to potable water intakes and irrigation use. It is felt that whole lake chemical treatments are not practical. The high cost is another barrier to use at Leland. Although fluridone is reportedly successful in the treatment of Brazilian elodea, large scale applications of SONAR (four treatments over a ten week period) made a few years ago in Lake Limerick in Mason County indicate otherwise. According to Limerick community member Dan Robinson (pers. comm. 1998), the Brazilian elodea infestation was initially knocked back 99.5 percent—success. But, by the end of the next season, Brazilian elodea had come back with a wide spread light growth throughout the lake. It now appears that Brazilian elodea has buds in the soil that survive broad scale chemical applications. Based on his experience with Lake Limerick, Robinson felt that, for long-term control, applications of the herbicide at higher than 20 ppb chemical concentration would need to be made.

GLYPHOSATE

Description The commercial brand of glyphosate known as RODEO is approved in Washington for aquatic use. This herbicide is a non-selective and broad spectrum chemical used primarily for control of emergent or floating leafed plants such as water lilies. Glyphosate is a systemic herbicide that is applied to the emergent vegetation of actively growing plants. It is rapidly absorbed and translocated throughout plant tissues, affecting the entire plant, including the roots.

Effectiveness and Duration Glyphosate is effective against many emergent and floating leafed plants but, according to the manufacturer, will not control plants that are completely submerged or those that have a majority of their foliage below the water. The herbicide binds tightly to soil particles on contact and thus is unavailable for root uptake by plants. Because of this strong adherence to soil particles, glyphosate is practically non-mobile and unlikely to migrate to groundwater. Initial evidence of herbicide effects includes the wilting and yellowing of plants, but this may not be apparent for seven days or more. These effects are followed by browning and death.

Advantages As a systemic herbicide, glyphosate is capable of killing the entire plant, producing long term control benefits. Glyphosate carries no swimming, fishing or irrigation label restrictions. It dissipates quickly from natural waters, with an average half-life of two weeks in an aquatic system. This herbicide has a low toxicity to benthic invertebrates, fish, birds, and mammals.

Disadvantages Glyphosate is a non-selective herbicide and therefore can affect susceptible non-target plant species. There is a possibility of drift during aerial application but it is expected to be minimal if label and permit instructions are followed. Though there are no irrigation label restrictions, there are potable water restrictions within one half mile of intakes in standing or flowing water. To make applications within the half mile limit, potable water intakes must be turned off for a minimum of 48 hours after the application or until a laboratory measured level of glyphosate in the water is below 0.7 ppm.

Costs Treatment costs by a private contractor average approximately $300 per acre, depending on the scale of treatment. Current bids for one application of RODEO to control reed canary grass in the upper 2000 feet of Leland Creek range from approximately $800 to $3800. At least two applications in a year would probably be necessary.

Permits The permit process is the same as for fluridone.

Appropriateness for Lake Leland Since RODEO is inactive for submersed plants, it would not control Brazilian elodea and would not be suitable for whole lake treatment.

Appropriateness for Leland Creek As previously mentioned, chemicals are not a control of choice for the community, but RODEO is seriously being considered to control reed canary grass in Leland Creek. This particular herbicide is inert in water, and though there are half-mile domestic water intake restrictions, there are no known potable intakes within that distance. Research with Ecology’s Water Resources section indicates that two surface water right certificates were issued, one in 1967 and the other in 1968 (Carroll pers. comm. 1998). These permits were issued for use two to three miles below the project area and it is not known if they are still in existence. RODEO can produce long term control and, if applied carefully perhaps with a backpack pump, can target specific plants. As mentioned earlier, a sensitive plant species, bristly sedge, has been detected along Leland Creek. Applications of RODEO would need to be selective if bristly sedge occurs in the spray area. Clallam County has used RODEO to control canary grass in the past year and should be consulted for their results before it is used at Leland. Also, it should be noted that there is a possibility of Brazilian elodea or another aquatic weed replacing the canary grass. It is believed, though, that these macrophytes would not impede water flow as much as the canary grass.

ENDOTHALL

Description Although Endothall is a contact-type herbicide, it is not readily translocated in plant tissues. Endothall formulations (active ingredient endothall acid, 7-oxabicyclo(2,2,1)heptane-2,3-dicarboxylic acid) are currently registered for aquatic use in Washington in either inorganic or amine salts. Aqueous or granular forms of the dipotassium salt of endothall, AQUATHOL (Elf Atochem), is permitted in State waters with stringent use restrictions on water contact, irrigation, and domestic purposes over and above label restrictions.

Effectiveness and Duration Being a contact herbicide, endothal kills only the plant parts that it contacts which is usually the upper stem portions. The entire plant is not killed so this herbicide is generally used for short term control of nuisance aquatic plants. Contact efficiency and regrowth from the unaffected root masses determine duration of control. Effective reductions in plant biomass can range from a few weeks to several months. In some circumstances, season-long control can be achieved but carryover control into the next season is not typical.

Advantages This type of treatment generally acts faster than translocating herbicides such as fluridone; evidence of tissue death is often apparent in one to two weeks. Cost wise this type of treatment is several hundred dollars per acre cheaper than fluridone over the same area. There is little or no drift impact using proper application techniques.

Disadvantages Endothall is a contact herbicide, so control is temporary. Non-target plants can be affected. Oxygen levels can become low. There are swimming use restrictions in Washington State of seven to eight days and also water use restrictions.

Costs Average costs run about $700 per acre.

Permits The permit process is the same as for fluridone.

Appropriateness for Lake Leland As previously mentioned, the use of whole lake chemical treatment is not a preferred option for the Leland community. Non-target plants could be affected. This particular herbicide requires swimming, fish consumption, irrigation, and domestic use restrictions. There is concern for the safety of this product in light of all the restrictions. Because only the upper part of the plant is killed, this product is not a good choice.

THE NO-ACTION ALTERNATIVE

Along with control alternatives to be investigated, the "no action" alternative should also be considered. There are several situations in which taking no action is appropriate. Consensus on control strategy may be unattainable or simply taking no action may be more favorable than using control options. No action might be the choice while waiting for new, more effective or environmentally friendly strategies to be developed.

If taking no action is considered, it is important to think about the eventual consequences to the target water body and perhaps surrounding water bodies, particularly in the case of a non-native invasive weed such as Brazilian elodea. The effects of dense weeds on water quality, fish and wildlife habitat, aquatic organisms, and recreation and tourism are all concerns to be addressed when considering the no action alternative. In order to maintain a perspective, the consequences of taking no action should be weighed against the costs and benefits of various plant control options.

As pointed out by David Christensen of Jefferson County Environmental Health (pers. comm. 1998), the no action alternative, though allowing for more infestation of Brazilian elodea, may cause an eventual decline. Research on Eurasian watermilfoil (Myriophyllum spicatum) has shown that control methods can lengthen the time for this plant to be dominant, and if left alone, it will become subdominant after a couple of decades. This may also be true for Brazilian elodea. In fact, Long Lake in Kitsap County has had a Brazilian elodea infestation for about 20 to 30 years and has been extensively studied by the University of Washington. In that lake, there has been a gradual decline in the biomass over time, but recently the biomass has resurged (Parsons and Hamel pers. comm. 1998). The residents of Long Lake are very unhappy about the plant and its impacts to recreation in the lake, and, currently, they are looking for an effective control.

Considering the fact that there are no large-scale control options without associated risks, the no-action alternative has appeal. Though the negative impacts of Brazilian elodea encroachment throughout the littoral zone of Lake Leland are substantial, some of these impacts, such as swimming safety, can be addressed using small-scale controls (hand-pulling and bottom barriers). At the present time, it is felt that no action on a large-scale, along with low risk control on a small-scale is a suitable combination.

Because of the complexities involving the flooding problem and reed canary grass in Leland Creek, taking no-action on the canary grass is not felt to be appropriate.

PREVENTATIVE TECHNIQUES

A prevention program that educates the public about noxious aquatic weeds is a valuable and important part of aquatic management planning. Weed control is not weed prevention. Education is a great prevention tool. This can be accomplished in the form of continued newsletters, flyers, and newspaper articles. More neighborhood workshops for training in the recognition of troublesome aquatic plants can help citizens with the early detection of different noxious weeds. Monitoring the areas that have used specific control methods such as hand-pulling and bottom barriers will add knowledge for future planning.

Public awareness of the problem can make a difference in the spread of exotic plants. Signs are being posted at the boat ramp and nearby lakes describing the invasive plant problem and the need to keep boats, trailers, and fishing gear free of plant fragments. Occasional weekend volunteers checking boat motors and trailers for noxious weeds at the boat ramp would reinforce this message. Boat washing stations have been used successfully at some lakes. Presently, there is no running water at the Leland boat launch, but this is a good preventative tool that may be able to be utilized in the future.


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Questions about this page?
Contact Kathy Hamel by e-mail at kham461@ecy.wa.gov