Milfoil Infested Lake Control Strategies.......

Eradication - Whole Lake Fluridone treatment

Fluridone (aquatic herbicide):

Fluridone is a systemic herbicide that kills the entire plant and is generally non-selective since most submersed plants will be killed or affected by a whole lake treatment. Fluridone inhibits the formation of carotene (pigment) in growing plants. In the absence of carotene, chlorophyll is degraded by sunlight. Because this is a slow process and the plants can “grow out” of this if fluridone is removed, the contact time between the plant and chemical needs to be maintained for many weeks. Sonar® and Avast!® are the trade names for aquatic herbicides that contain fluridone as the active ingredient. The liquid formulation of fluridone has been used for whole-lake milfoil eradication projects. A granular formulation is also available, but has not been used for whole lake treatments.  The premise for using fluridone as an eradication tool is that milfoil rarely produces viable seeds, so killing the vegetative growth will prevent spreading through fragmentation. Milfoil is particularly susceptible to fluridone and it is theoretically possible to achieve 100 percent kill. If all the milfoil plants are killed by fluridone treatment the only way that milfoil can reinfest the lake is to be reintroduced or germinate from seeds. Germination by seeds is considered rare.   

Waterbodies suitable for whole-lake fluridone treatment:

Lakes and ponds suitable for whole-lake fluridone treatment are heavily infested with Eurasian watermilfoil throughout the littoral zone. Fluridone is not suitable for spot treatments (sites less than five-acres within a larger waterbody) since it is difficult to maintain enough contact time between the plant and the herbicide to kill the plant. If milfoil is limited to patches within the littoral zone, 2,4-D may be a more effective treatment method (see the 2,4-D milfoil eradication strategy). Due to the high treatment costs, fluridone treatments have been limited to smaller sites in Washington. The largest lake in Washington where this method has been used for milfoil eradication has been Long Lake (about 330 acres). In larger lakes, treatment of selected coves or embayments is possible, although milfoil will eventually reinvade from untreated areas. 

Special considerations:

While there are no swimming, fishing, or drinking water restrictions when fluridone is in the water, the label warns against using the water for irrigation for seven to thirty days after treatment. Even at the low fluridone concentrations used to treat milfoil, some terrestrial plants may be sensitive to fluridone if they are watered with treated lake water.  

Washington has had excellent success using this fluridone for milfoil eradication/control, but there is no guarantee that every lake group who tries this method will achieve the same results. Each site is different and many environmental factors may affect the treatment. Developing a site-specific plan for each lake is crucial to identifying environmental factors or concerns that may impact the treatment outcome. A permit called a National Pollutant Discharge Elimination System Permit (NPDES) permit is needed to treat waterbodies with aquatic herbicides. You can obtain NPDES coverage under the Washington Department of Agriculture Permit for noxious weed control. Click here for more details of the permitting process.

Description of a milfoil eradication project using fluridone:

When the project goal is eradication, a whole lake fluridone concentration of 12-15 ppb (parts per billion or mg/liter) should be maintained in the lake for approximately ten weeks during the spring and/or summer. While it is possible to achieve successful milfoil control at lower concentrations (as low as 3-6 ppb), these higher levels are recommended to ensure that all milfoil plants are killed.  

Before application, the lake volume must be determined to ensure fluridone is applied in a sufficient amount to result in the target whole lake concentration. If the lake is shallow and not thermally stratified, concentrations throughout the water column must remain in the 12-15 ppb range. If the lake is deep and thermally stratified (warm above and cold below), these concentrations can be maintained in the epilimnion (warmer surface layer of water) rather than throughout the water column.  

Treatment costs will vary based on lake surface area, water volume treated, and the number of treatments needed to maintain the target concentration for ten weeks. The SePRO Company (distributor for Sonar®) has developed a new patented test called planTEST™ that their preferred applicators may use. Treated plants are collected a few weeks prior to treatment and planTEST™ determines the concentration of Sonar® needed to kill the target weed. If milfoil in the lake is particularly susceptible to fluridone, it may be possible to reduce the concentration of fluridone needed to effectively treat the infestation.  

Treatments can start as soon as milfoil begins rapidly growing. This can be as early as April or May and as late as early July and is site-specific. Much depends on the timing windows for salmon usage (provided by Washington Department of Fish and Wildlife for each waterbody) since juvenile salmonids should not be exposed to chemicals. Another critical factor particularly in western Washington is water flow. A heavy rainfall may wash the herbicide out of the system. For deeper lakes, treatment should be delayed until the thermocline develops and stabilizes in summer. For these reasons, fluridone treatments in Washington often begin in June or July rather than earlier.   

Fluridone is applied in a liquid formulation by sub-surface injection from trailing hoses by a state-licensed applicator. About a day or two after treatment, water samples should be collected to determine fluridone concentrations. The number of samples required depends upon the size and shape of the lake. In a long narrow lake, three samples may be enough to determine lake concentration. In a small round lake, one sample taken in the middle may be sufficient. In a lake with many coves or channels, a number of samples may be needed to determine a whole lake concentration. Testing the water ensures that the target concentration of fluridone has been met. The SePRO Company and Griffin LLC (distributor for Avast!) both have fluridone analysis test kits. Test results can be available within 48 hours and each sample costs about $100. Other laboratories can also perform fluridone analysis, but turn around times for results may be longer.

Fluridone concentrations are maintained in the lake over time by the application of additional herbicide at about bi-weekly intervals or as needed. To determine how much herbicide to add, water samples are collected about 10 to 14 days after the initial treatment and analyzed for fluridone. Generally during this two-week period, fluridone concentrations decrease by about half, due to plant uptake and exposure to sunlight. Fluridone is also more persistent in cooler waters. After fluridone concentrations are determined, the applicator applies enough herbicide to the lake to bring the whole lake concentration back up to the 12-15 ppb range. This scenario continues until fluridone concentrations have been held at 12-15 ppb in the lake for ten weeks. This fluridone concentration and exposure time should be sufficient to kill milfoil plants. During a typical treatment, the applicator may apply fluridone to the lake four times.  

The SePRO Company has also developed a new patented test called effecTEST™ that their preferred applicators may use. Treated plants are collected at about five to six weeks after the initial treatment and effecTEST™ determines whether these plants have received enough herbicide to kill them or if a higher (or lower) concentration is needed.  

General impacts of fluridone treatment: 

There are significant impacts to the waterbody during and following treatment. Fluridone is a generally non-selective herbicide, which means most submersed plants and some floating leaved plants will be killed by fluridone during the treatment. Emergent species like cattails will be impacted but will recover. A week to three weeks after the initial treatment, observers will see the growing tips of aquatic plants bleach pink to white. Water lilies will appear bleached and cattails and other emergent species may look variegated. Since this is a slow process, low oxygen conditions do not develop. The plants eventually drop out of the water column by about six weeks post-treatment.  

While there is no direct toxicity of fluridone to animals, the loss of habitat does cause indirect impacts. The smaller fish lose their hiding places and because the larger fish can find them easily, they have greater chances of being eaten. Waterfowl that eat vegetation tend to move onto other vegetated waterbodies while waterfowl that eat fish enjoy better fishing opportunities on the treated lake. Sometimes increased algal blooms are observed in the year of treatment and for a year following treatment. However, eventually the lake reaches a new equilibrium and native aquatic plants recover. Naturally occurring plants have viable seeds, tubers, and overwintering buds that allow them to revegetate the lake the year following treatment, while milfoil does not. In Washington the colonization of the lake bottom by plant-like algae called brittlewort (Nitella spp.) and stonewort (Chara spp.) is often observed following a fluridone treatment. This is because algal species are resistant to fluridone and removing milfoil opens up space for them to colonize.  

Up to 100 percent of the Eurasian watermilfoil in the lake should be killed. However in inlets or areas where the herbicide may be diluted by flowing water (including in-lake springs), milfoil may be undertreated and must be physically removed if eradication is to be successful. These areas should have been identified during plan development and alternative methods planned for milfoil removal. Undertreatment or no treatment of milfoil in inlet areas may result in the lake being reinfested unless immediate management methods are undertaken.  

Follow-up:

For lakes that are heavily infested with milfoil, the goal of eradication should only be sought when lake residents are willing to finance and conduct the follow-up monitoring and treatments that are essential to ensure long term success. The littoral zone of the lake should be thoroughly inspected by divers in the fall of the treatment year and the next spring as well to identify any milfoil plants that may have been undertreated. Areas where this might happen include areas of lake bottom with springs or near inlet streams. Any remaining milfoil plants should be hand pulled or covered with bottom barriers (See: Eradication - Hand Pulling and Bottom Barrier Installation). Diver and surface inspections should continue at least twice a year during the growing season on an ongoing basis. Survey work should be as frequent as can be afforded, since small milfoil plants may be easily overlooked. Often divers report finding two to three foot tall milfoil plants in areas that they had extensively searched only three weeks earlier. As native plants recover, it will become more difficult to locate any milfoil plants. 

Very important note!

In most Washington lakes treated with fluridone, milfoil is found growing in the lake from two to five years later. It is suspected that milfoil is reintroduced via boating activity, since it is often discovered near a public boat launch. However, anecdotal evidence also suggests that milfoil seeds can germinate during dewatering. During long, dry summers lake levels may drop. Check these areas for milfoil growth after the water returns. As long as the lake group has continued the survey work, these new introductions can be identified quickly and targeted for removal before milfoil reestablishes. In treated lakes where lake groups have continued the diver and surface inspections, milfoil remains at extremely low levels and recreation, fishing, and habitat remain healthy. In the few lakes where inspections did not continue, milfoil reinvaded and the lakes returned to pre-treatment infestation levels. It is interesting to note that the one lake where milfoil never returned after treatment is a canoe and kayak lake only and located on an island (Goss Lake).  

Follow-up is the key!

While it is very difficult to totally eradicate milfoil from a lake forever, extensive and long-term follow-up activities make it possible to maintain extremely low levels of milfoil that will not impede recreational activities or impact native plant communities. As an example, Long Lake in Thurston County was treated with fluridone in 1991. In 1995, milfoil was discovered growing near the public boat launch. Since then the lake residents and Thurston County have been successfully maintaining extremely low levels of milfoil in the lake by surface and diver survey and hand pulling. In 2001 about 90 pounds total wet weight of milfoil was removed from the 330-acre lake (Ryan Langen, personal communication). Much less milfoil was found in 2002. These activities are not inexpensive, but are considered a necessary cost to maintain this lake in good condition for recreation and habitat. Should these management measures cease, milfoil would probably reinfest the lake within three to five years.

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Contact Kathy Hamel by e-mail at kham461@ecy.wa.gov

Last Updated October 09, 2005

Milfoil Infested Lake Control Strategies.......

Eradication – 2,4-D treatment

2,4-D (aquatic herbicide):

2,4-D is a relatively fast-acting herbicide that kills the entire plant (systemic herbicide). Its mode of action is primarily as a stimulant of plant stem elongation. This herbicide is considered to be “selective” for milfoil because it generally targets the broad-leaved plants (dicots) like milfoil. Most other aquatic plants are monocots (grass-like) and are unaffected by 2,4-D.  Navigate® and Aqua-Kleen® are granular 2,4-D products registered for aquatic use and DMA*4IVM® is a liquid formulation.  

Waterbodies suitable for 2,4-D treatment:

Sites suitable for treatment include lakes or ponds partially infested with Eurasian watermilfoil such as waterbodies where milfoil has recently invaded, but where the extent of the infestation is beyond what can be removed by hand pulling or bottom screening. In these situations an herbicide, like 2,4-D, that is effective for spot treatment can be used to reduce the amount of milfoil so that hand pulling can remove any milfoil plants that are not killed. 2,4-D is suitable for spot treatment because it is a fast-acting herbicide that only needs a 48-hour contact time with the plant. 2,4-D can be used for milfoil control in heavily infested lakes, but it does not provide the nearly 100 percent kill of the herbicide fluridone. Because many plants remain alive and scattered throughout the littoral zone after 2,4-D treatment, hand pulling extensive areas after treatment may not be effective in heavily infested lakes. Lake residents must be willing to fund the follow-up activities necessary to ensure continued milfoil eradication (or maintenance at extremely low amounts).  

Special considerations:

Water users need to be identified prior to 2,4-D application. Water within the treatment areas cannot be used for drinking until 2,4-D concentrations have declined to 70 ppb and water used for irrigation cannot be used until 2,4-D concentrations are 100 ppb or less. If water users do not have other water sources, the project proponents must arrange for alternative water supply during the time that 2,4-D is in the water. In Washington, testing has shown that water both inside and outside of the treated area is generally below the drinking water standard three to five days after treatment. A permit called a National Pollutant Discharge Elimination System Permit (NPDES) permit is needed to treat waterbodies with aquatic herbicides. You can obtain NPDES coverage under the Washington Department of Agriculture Permit for noxious weed control. Click here for more details of the permitting process.

Description of a milfoil eradication project in Washington using 2,4-D:

Lakes where 2,4-D is being used for milfoil eradication in Washington typically have milfoil scattered in patches within the littoral zone. The lake is surveyed immediately prior to herbicide application and milfoil locations are mapped and Global Positioning System (GPS) points established.  

Herbicide application can begin as soon as milfoil starts rapidly growing. Effective treatments can be made as early as April or May and as late as early September. Timing is also dependent on salmon usage since juvenile salmonids should not be exposed to chemicals. Treatment in the spring/summer should be followed by a late summer survey and possible retreatment if large patches remain or if more milfoil is discovered in untreated areas of the lake.  

A month after the initial 2,4-D treatment, the littoral zone of the lake should be thoroughly inspected by divers to identify and map remaining milfoil plants. Sparse populations of remaining milfoil plants should be hand pulled or covered with bottom barrier. Larger, denser patches may need to be treated again with 2,4-D, although in that case some assessment should be made as to why the initial treatment was ineffective. Diver and surface inspections should continue at least twice a year during the growing season. Survey work should be as frequent as can be afforded since small milfoil plants may be easily overlooked within the native plant beds. Often divers report finding two to three foot tall milfoil plants in areas that they had extensively searched only three weeks earlier.  

The herbicide is available in a granular and liquid form and application must be made by a state-licensed applicator. The granular formulation of 2,4-D is typically applied using a bow-mounted centrifugal or blower-type spreader and uniformly spread over the water above the milfoil beds and slightly beyond. The clay particles sink to the bottom or are caught up in the plants. The herbicide slowly releases from the clay over the next day. Granular formulations are generally recommended for spot treatment since liquid applications may have more tendency to drift away from the milfoil beds. When the liquid formulation is used, it is applied using subsurface trailing hoses. In both cases, if the project is funded by an Ecology grant or if there are irrigation or drinking water concerns, monitoring will be required. A 2,4-D analysis test kit should be available soon or environmental laboratories can also perform 2,4-D analysis. Rapid turn around of results costs more.  

General impacts of 2,4-D treatment:

2,4-D is a selective herbicide and milfoil is particularly susceptible at a labeled rate of about 100 pounds per acre (granular product). At this rate impacts to other aquatic plant species are minimal. Even if applied at higher rates there are only a few other aquatic plant species that are affected by 2,4-D. A study conducted in Loon Lake Washington showed that Eurasian watermilfoil was the only aquatic plant whose growth was statistically reduced by the 2,4-D application (Parsons, et. al, 2001). In the Loon Lake study up to 98 percent of the Eurasian watermilfoil biomass in the treatment plots was removed after the July treatment. Click here to see Ecology's risk assessment for the environmental and human health impacts of 2,4-D.

A few days after the 2,4-D treatment, observers will see the growing tips of milfoil plants twist and look abnormal. These plants will sink to the sediments usually within one to two weeks of treatment. Unless treatment takes place in dense beds of milfoil, it is unlikely for low oxygen conditions to develop. Results of spot treatment may be variable depending on water movement, size of treatment plot, density of milfoil, weather conditions, underwater springs, etc.  

Follow-up:

Follow-up is essential to ensure the success of eradication. Used alone, 2,4-D is not an eradication tool. Some plants survive the treatment and regrow, so these plants must be removed by other means. Surveys done in Minnesota indicated that, 2,4-D use did not result in eradication of milfoil over the long-term (Crowell, 1999). Treated lakes for which there was no follow up survey work or treatment eventually ended up with milfoil throughout the littoral zone. There is some anecdotal evidence that milfoil plants may become resistant to 2,4-D. Applicators have reported that milfoil in Loon Lake did not respond as well to treatment in 2002 as it had in previous years. If this occurs and the plant population is too large to be hand removed, consider using endothall, diquat, or (when approved by Ecology) triclopyr. There is also some anecdotal evidence that milfoil may germinate from seeds in areas where water levels dropped and then returned. This may happen in low rainfall or low runoff years. It is important to check those areas when the water returns to remove any milfoil that may have germinated. 

Follow-up is the key!

Once milfoil is discovered in a lake, it generally requires continual maintenance to keep it at low levels. Even if milfoil appears to have been eradicated it often is reintroduced by boaters or may germinate from seeds. As long as the lake group continues surveying on a yearly basis, new introductions can be identified quickly and targeted for removal before milfoil can re-establish in the lake. In treated lakes where the lake group has continued diver and surface inspections, milfoil remains at extremely low levels, without impacts to habitat or recreational activities.  

References:

Crowell, W.J. 1999. Minnesota DNR tests the use of 2,4-D in managing Eurasian watermilfoil. Aquatic Nuisance Species Digest. 3(4):42-46.

Parsons, Jenifer K.; K.S. Hamel, J.D. Madsen and K.D. Getsinger. 2001. The Use of 2,4-D for Selective Control of An Early Infestation of Eurasian Watermilfoil in Loon Lake, Washington.  J. Aquat. Plant Manage. 39:117-125.

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

Last Updated October 09, 2005

Milfoil Infested Lake Control Strategies.......

Control- Littoral Zone Endothall treatment

 Endothall (aquatic herbicide):

Endothall (active ingredient) is a fast-acting contact herbicide (an herbicide that burns back the above-sediment vegetation, but doesn’t kill the roots) that is believed to disrupt the plant biochemical processes at the cellular level. The dipotassium salt of endothall is used for aquatic plant control and is formulated as Aquathol® K (liquid) and Aquathol® Super K Granular. The Washington State Department of Ecology recently completed a risk assessment and an environmental impact statement for endothall. The risk assessment and the impact statement can be viewed by clicking here.  

Endothall has been used for years in Washington lakes to spot treat milfoil along shorelines because it is rapidly-acting, and when used at higher concentrations (2-3 parts per million (ppm) needs only a short contact time to remove milfoil vegetation. Recently, lower concentrations (1-1.5 ppm) of endothall have been used to treat milfoil in whole lake or littoral zone treatments. Milfoil can be controlled (vegetative growth removed) at 1 mg/l active ingredient endothall with an exposure time of 48 to 72 hours. At this concentration, endothall impacts some native plant species to a lesser degree (Skogerboe and Getsinger, 2001).

The benefit of using low levels of endothall is to remove exotic weeds like milfoil, while allowing native species to recover. While this is not an eradication technique, it may be useful for maintaining more acceptable levels of milfoil in a lake by periodically treating the littoral zone with low concentrations of endothall. It is possible that treatments can occur as infrequently as every three years. Ecology, along with the Department of Fish and Wildlife, and the endothall manufacturer, Cerexagri, is conducting a study on a small western Washington lake (Kress Lake) to determine the efficacy of using low levels of endothall to control milfoil.  

Waterbodies suitable for endothall treatment:

Whole littoral zone treatment with endothall cannot be considered as an eradication method. Endothall will suppress the growth of milfoil and may allow native plants to recover and therefore increase species diversity within a lake. Lakes and ponds considered suitable for littoral zone treatment are heavily infested with Eurasian watermilfoil. This method may be used where it is considered too expensive, or the waterbody is too large to use milfoil eradication strategies.  

Special considerations:

The endothall label has a three-day fish consumption restriction in the area of treatment and an irrigation and stock watering restriction for 14-days after treatment. Ecology advises waiting 24 hours after any herbicide treatment before swimming, although there is no official label restriction for swimming. Care must be taken with the application so that low oxygen conditions do not develop as plants decompose. 

Any whole lake or widespread herbicide treatment, such as littoral zone endothall treatment should be conducted under an integrated aquatic vegetation management plan. A permit called a National Pollutant Discharge Elimination System Permit (NPDES) permit is needed to treat waterbodies with aquatic herbicides. You can obtain NPDES coverage under the Washington Department of Agriculture Permit for noxious weed control. Click here for more details of the permitting process.

Description of the Kress Lake project, using endothall:

A detailed report about the treatment and sampling methodology and the results of the Kress Lake project can be seen in Ecology’s Aquatic Plants Technical Assistance Program: 2001 Activity Report. The information/data below were taken from that report. The project is still ongoing and additional data will be collected in August 2002 and June 2003.  

Kress Lake, a 30-acre manmade lake in Cowlitz County, is a popular fishing lake with a nuisance population of milfoil.  

Kress Lake is owned and managed by Washington Department of Fish and Wildlife as a warm water fishery (bass, channel catfish, and sunfish) and has no inlet or outlet. Trout and surplus steelhead are also stocked into this landlocked lake. Prior to treatment, aquatic plants were found growing throughout the lake with milfoil as the dominant species. Both fishing and the fishery of the lake were being negatively impacted by the milfoil plants (Stacey Kelsey of Fish and Wildlife, personal communication). She reported that excessive vegetation was contributing to a stunted fish population, and milfoil mats, especially along the shoreline, were interfering with fishing. The endothall study was undertaken to see if a low concentration of endothall could selectively remove milfoil, increase species diversity, and improve fishing and the fishery.   

On June 21, 2000, a state-licensed applicator applied Aquathol® K at rate of 1.5 ppm to ten acres around the edge of the lake. A second treatment took place a month later with an additional 10 acres treated from the shorelines toward the center of the lake using the same application rates.  

Assessment of the treatment project is ongoing. Three months after treatment the endothall treatment reduced the frequency with which the vascular plants (flowering plants like milfoil) were found, while not affecting the macroalgae muskgrass (Chara sp.). During this period, vascular plants were reduced to the point of eliminating plant cover completely in locations throughout the lake. By one year after treatment and throughout that summer (June 2001 and September 2001) the frequency of muskgrass appeared to level-off while some of the vascular plants increased (e.g. waterweed, (Elodea candensis), milfoil (M. spicatum), and bladderwort (Utricularia sp.). This recovery appeared to fill in areas left bare of plants the previous summer.  The pondweeds (Potamogeton sp.) did not appear to be rebounding. 

Two species showed a significant change in their biomass before and after treatment. The biomass of waterweed (native plant species) increased significantly one year after treatment. About one third less milfoil biomass was collected after treatment (76 g/m² - before treatment versus 23 g/m² - one year after treatment). 

The species list from each sample date shows that the species diversity was greatest in June 2001; one year after treatment. A total of 12 different plant types were present at that time. This is almost double the number found before the herbicide treatment. The number of plant types observed decreased to 9 by the September 2001 sampling event.  This may have been due to sampling variability, increased dominance by a few species making locating less common species more difficult, or the seasonal die off of selected species.

Endothall (Aquathol KÒ) significantly reduced both the biomass and frequency of observation of milfoil, over the study period. However, by 1.3 years after treatment milfoil was showing a significant increase in frequency, so the duration of the control may be ending. The results also show an increase in overall submersed aquatic plant species diversity one year after treatment. 

Although the June 2002 data have not been statistically analyzed, surprisingly milfoil did not appear to have increased in frequency or biomass when compared to the previous year (Kathy Hamel, personal observation).     

General impacts of endothall treatment:

Generally endothall is used to spot treat areas and therefore impacts are not widespread. Using low levels over the lake littoral zone does cause adverse impacts in the short term, since many vascular plants are affected by the treatment. Within a few weeks of treatment, most plants in the treated area are brown and dropping from the water column. In Kress Lake, an algal bloom was observed a few weeks after the herbicide treatment. This may have been caused by the nutrients released from the decaying plants. (Note: an algal bloom was also observed in August 2002, although no herbicide treatment had taken place for two years. Many lakes are naturally nutrient-enriched.) Sampling ten weeks after treatment showed mostly dead and decaying plants lying along the bottom and bright green healthy muskgrass populations. A year after treatment, the native plant community was recovering, but milfoil, though present, did not dominate the plant population.  

Fish and Wildlife staff have been pleased with the results, indicating that anglers are now able to fish without tangling their gear in milfoil.   

Follow-up:

This is potentially a new method available for the control of milfoil in heavily infested lakes. The results from Kress Lake have been excellent. The lake was treated in 2000 and no further treatment was needed in 2001 or 2002. At this stage of assessment, we do not know how often the lake will need to be treated to continue the suppression of milfoil. 

References:

Parsons, J., B. Dickes, and A. Fullerton, 2001. Aquatic Plants Technical Assistance Program: 2001 Activity Report. Washington Department of Ecology 

Skogerboe, J.G. and K.D. Getsinger. 2001. Endothall species selectivity evaluation: southern latitude aquatic plant community. J. Aquat. Plant Manage. 39:129-135.

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