NYSDEC

Division of Water

A Primer on Aquatic Plant Management

in New York State

April 2005

- DRAFT -

4. Aquatic Herbicides

� Principle

Aquatic herbicides (pesticides) are chemical compounds used to kill undesired macrophytes and restrict further vegetation growth. Herbicides are used primarily to kill specifically-targeted aquatic vegetation species, whether floating, emergent, or submerged. They also provide short-term clearance for recreational areas and navigational channels. As with other in-lake weed management strategies, herbicides address neither the cause nor the source of the problem.,

Herbicides are applied in either liquid or granular form. In most cases, the chemicals are applied to the water directly overlying the problem area. Most granular herbicides are activated through photodegradation of the granular structure, releasing the active chemical. These chemicals either elicit direct toxicity reactions or affect the photosynthetic ability of the target plant. The plants die and degrade within the lake. Some herbicide residuals sink to the lake sediment, providing some additional temporary control of vegetation. For some herbicides, however, once the granules sink to the bottom and out of the photic zone (area penetrated by light), photodegradation ceases, and the chemical is no longer effective. .

There are generally two classes of aquatic herbicides. Contact herbicides affect only those portions of the plant contacted by the herbicide, usually through (plant) toxicity. Systemic herbicides affect metabolic or growing processes within most or all of the plant, often translocating from the leaves to the root system. In general, systemic herbicides tend to take longer to work, but are often more effective at controlling plants for a longer period. Contact herbicides generally work more quickly but have less longevity. However, individual herbicides within these classes have different modes of action for either inhibiting plant growth or destroying the plant itself.

Both classes of herbicides are registered for use in NYS and since many herbicides contain toxic chemicals, only licensed applicators should place herbicides in lakes. Most herbicides can be used in most lakes, but some lakes used for a domestic drinking water source may have restricted uses for certain herbicides.

Correct timing of the chemical application is important, since seeds can germinate and roots can sprout even when the parent plants are killed off. The specific time for the application will depend on the specific target weed, required dosage rate, water temperature, water chemistry characteristics of the lake, weather conditions, water movement and retention time, and recreational use of the lake. Curly-leaf pondweed has a growing season from mid-fall through early summer, while Eurasian watermilfoil usually grows from early spring through the end of the summer. Herbicide applications must consider the timing of the growing season relative to the algae levels (since photodegradation of herbicides may be slower when algae reduces lake clarity), ice cover, and the effect the chemical application will have on the recreational use of the lake. Most herbicides have restrictions on the use of the water body immediately after treatment, lasting up to 30 days, depending on the dose rate or use of the lake.

Follow-up monitoring should track the fate of the applied chemical, and changes in the plant communities, water quality conditions, and impaired uses. The effectiveness for any given herbicide treatment varies with the treatment design, and the conditions of the lake and treatment site listed above (Westerdahl and Getsinger, 1988). In general, for contact herbicides the effectiveness of an herbicide treatment will last anywhere from several weeks to several months, usually corresponding to a single growing season. Since seeds and roots frequently are not affected by treatment, once the chemicals have degraded or washed out of the system, plant growth will resume, and reapplication may be necessary. Effectiveness rarely carries over to the next growing season. For systemic herbicides, treatment effectiveness is often not observed for at least three to four weeks (and often up to six to eight weeks), although plant control with these herbicides have be

Case Study- Aquatic Herbicides

Lake Setting: Snyders Lake is a 110 acre lake found in the Capital District region of New York State, used primarily by local residents for swimming and boating

The Problem: While more than 20% bottom coverage of rooted aquatic plants had been reported in the lake from the time of the biological surveys of the 1930s through at least the late 1980s, watquality issues, particularly winter and spring blooms of the reOscillatoria rubescens and complaints of turbidity by nearby development had dominated discussions about the management of the lake. Weeds had not been sufficiently dense to warrant active management until the late 1990s, but at that time, dense aquatic plant beds were dominated by Eurasian watermilfoil throughout the littoral zone.

Response: After significant public debate about the need for management and the available alternatives, the Lake Association of Snyders Lake voted to apply fluridone to the entirety of the lake in the spring of 1998. A combination of private funds and state local assistance grants were used to offset the appx. $25,000 cost for the treatment.

Fluridone was applied at a rate of approximately 13-18 (parts per billion, or ppb), and was tracked by the lake association at several locations and depths for about 5 months. Furidone residuals remained above 6ppb for at least 55 days, above 4ppb for more than 115 days, and were still above 2ppb for at least 155 days. The greater-than-expected longevity was due to a combination of factors, including a dry spring and summer resulting in little outflow (through a small sand-bagged outlet), a slow drop of the thermocline, and a lower rate of photodegradation.

Results: By the end of the summer in the year of treatment, there was no evidence of any submergent aquatic plants in the lake. Scattered submergent plant growth returned the following summer, although this was limited primarily to macroalgae (Chara spp.) and isolated single stems of Eurasian watermilfoil, mostly in thin sediments. In 2000 and 2001, however, extensive billowing beds of brittle naiad (Najas minor) were found in the areas where sediment was thick andorganic, and small quantities of other native plants (large-leaf pondweed, leafy pondweed, macroalgae) were found in isolation throughout the littoral zone. Eurasian watermilfoil was still largely limited to small patches, mostly in the thinner sediments. Maps showing aquatic plants in the lake prior to treatment and in 2000 look very similar, with the brittle naiad replacing the milfoil. However, while the brittle naiad grew very bushy below the surface, unlike tmilfoil, it did not form de

� Target

Target Plants At the dosage rates allowed in New York State lakes, most aquatic herbicides are not selective. If applied when plants are actively growing, at concentrations allowed by the label, most plants within the treatment zone will be removed by these herbicides. Selectively can be increased by timing the applications to when the target plants are preferentially growing. To a lesser extent lower dosage ra

In New York State, the most frequ

endothol, glyphosate, and fluridone. Diquat is a contact herbicide used to control emergent species such as cattail; floating species such as duckweed; and submerged species such as coontail, milfoil, nitella; and some varie

algae control. 2,4-D is a systemic herbicide used for controlling a wide variety of emergent, floating, and submerged species, primarily Eurasian milfoil, coon

Endothol is a contact herbicide used primarily for control of coontail and most pondweeds, including curly-leafed pondweed. It stays in the water column longer than either diquat or 2,4-D.

Glyphosate is a contact herbicide used almost exclusively on emergent and floating plants, especially cattail and waterlily.

Fluridone is a systemic herbicide used extensively in recent years for the control of Eurasian watermilfoil and curly-leafed pondweed. It has been used at low dosage rates to attempt to manage target plants while preserving non-target plants.

Case Study- Aquatic Herbicides (cont)

Results (cont): After 2001, milfoil recolonized large patches of the littoral zone, although it was still much less dominant than prior to treatment, due to the well-established brittle naiad beds. The milfoil spread to some areas not previously occupied by any macrophytes. The coverage and density of the milfoil/brittle naiad beds were significant enough to trigger a spot teatment with endothal in the summer of 2004 in the areas of the lake with the highest macrophytes coverage (and, perhaps not coincidentally, the highest sedimentation rate).

Most antidotal information from lake residents and visitors indicate a general satisfaction with the results of the initial treatment, with few reported complaints from anglers about the lack of a fishing edge or loss of any year-classes. Water quality conditions were relatively stable throughout the treatment and subsequent response period, and reports of blue-green algal blooms or other water quality complaints were less common than in most previous five-year periods, despite the potential available of nutrients not taken up by the rooted plants. However, this may have been more a function of more favorable weather conditions.

Lessons Learned: Aquatic plants appear to recover (or get re-introduced) after a long

Source: Kishbaugh, S.A. 2002. Assessment of Eurasian watermilfoil control with Sonar at Snyders Lake, NY: 1998-2001. Presentation to the NEAPMS annual conferenc

The table below indicates the susceptibility of common New York State submergent, floating, or emergent plants to these herbicides.

� Advantages

Unlike many other in-lake management techniques, aquatic herbicides can be applied directly to the problem plants, although many of the herbicides registered in New York State are so water soluble that they do move somewhat out of the treated areas. Aquatic herbicides are available for immediate or long-term control of nuisance plants, and some of these herbicides have been shown to be somewhat selective if applied at the right time (usually very early or very late in the growing season, corresponding to when target plants, such as invasive exotic weeds, are preferentially growing) and at the right dosage rate.

Aquatic herbicides have been effective at providing at least temporary control of Eurasian watermilfoil in some New York State lakes. This pernicious exotic weed has not been consistently (or at least somewhat selectively) controlled by any of the other whole-lake treatment strategies. While generally cost-prohibitive for treatments of very large areas or very large lakes, aquatic herbicides are often less expensive than other large-scale plant control methods.

� Disadvantages

Chemically-treated lakes may experience some significant side effects. Because herbicides kill plants primarily through toxic response, the toxicity of the herbicide to non-target plants and animals can be of great concern. Short-term impacts of aquatic herbicides have been fairly well studied for most of the inhabitants of lakes and the surrounding environment, and have been deemed to be an �acceptable risk� if applied in the appropriate manner. In general, humans and most animals have high tolerance to the toxic effects of herbicides presently approved for use in lakes. This is especially true of the newer generation herbicides that have been formulated to impact metabolic processes specific to chlorophyll-producing plants. However, the long-term impact of herbicides on humans and other plants and animals in the environment continues to be poorly studied. High herbicide dosages can elicit toxic response for the applicator and protective gear must be worn.

Non-target plants may not be resistant to the herbicide. If a wide variety of plant species are eradicated by herbicide treatment, the fast-growing ("opportunistic") exotic species that were the original target plants may recolonize the treatment area and grow to levels greater than before treatment. There are only very limited data on the effect of specific herbicides on plant species in New York State lakes. It is not clear if the target plant species listed on the herbicide labels can be completely controlled without adversely affecting non- target species at any given lake.

Impact of NYS Registered Herbicides on Common Nuisance Aquatic Plants

Susceptibility to Herbicide:
Aquatic Plant	Diquat	2,4-D	Endothal	Glyphosate	Fluridone
Emergent Species
Lythrum salicaria (purple loosestrife)	low	low	low	high	low
Phragmites spp (reed grass)	low	low	medium	high	low
Pontederia cordata (pickerelweed)	low	medium	low	medium	low
Sagittaria spp (arrowhead)	low	high	low	high	low
Scirpus spp (water bulrush)	medium	high	low	high	low
Typha spp (cattails)	medium	medium	low	high	medium
Floating Leaf Species
Brasenia schreberi (water shield)	medium	medium	medium	low	medium
Lemna spp. (duckweed)	high	medium	medium		low	high
Nuphar spp (yellow water lily)	low	medium	medium	high	medium
Nymphaea spp (white water lily)	low	medium	medium	high	medium
Trapa natans (water chestnut)	low	medium	low	low	low
Submergent Species
Ceratophyllum demersum (coontail)	high	medium	high	low	high
Cabomba caroliniana (fanwort)	medium	medium	high	low	high
Chara spp. (muskgrass)	low	low	low	low	low
Elodea canadensis (common waterweed)	high	medium	low	low	high
Heteranthera dubia (water stargrass)	high	high	medium	low		medium
Myriophyllum spicatum (Eurasian watermilfoil)	high	high	high	low	high
Najas flexilis (bushy pondweed)	high	medium	high	low	medium
Potamogeton amplifolius (largeleaf pondweed)	low	low	medium	low	medium
Potamogeton crispus (curly-leafed pondweed)	high	low	high	low	high
Potamogeton robbnsii (Robbins pondweed)	low	low	medium	low	high
Stuckenia pectinatus (Sago pondweed)	high	low	medium	low	medium
Utricularia spp (bladderwort)	high	medium	low	low	high
Vallisneria americanum (eelgrass)	low	low	medium	low	medium

*- adapted from Holdren et al., 2001 and others

When herbicides are applied in a lake environment, the affected plants drop to he bottom of the lake, die, and decompose. The resulting depletion of dissolved oxygen and release of nutrients could have detrimental ef-fects on the health or survival of fish and other aquatic life as well as stimulating new plant growth.

The effectiveness of systemic herbicides is often delayed. Given that the most effective treatment windows correspond to periods bounded by the onset of thermal stratification in the beginning of the year (to avoid treating the entire lake rather than the upper warmer waters where plants tend to grow) and by the onset of fish spawning and native plant uptake (when surface waters warm to > 50�F), plant dieoff may often not occur until early to mid summer. This means that plant control from systemic herbicides might not be �enjoyed� by lake residents until much of the recreational season has passed.

� Costs

Herbicide costs will vary with the chemical brand and form (liquid or granular), required dose rate, applicator fees, and frequency of application. Typical costs for using herbicides are approximately $200-400 per acre of treated area per treatment, with the majority of these costs associated with the raw materials.

� Regulatory Issues

Herbicide use in New York State requires a permit from the DEC regional environmental permits office, in compliance with the Environmental Conservation Law. If all or part of the lake contains a regulated wetland, an additional wetland permit may be required. For those lakes for which the generic Environmental Impact Statement (EIS) prepared by the manufacturers of these herbicides is deemed insufficient to address the myriad of permitting issues that might be appropriate in the lake, a site-specific EIS may be required to issue these permits. The Adirondack Park Agency will require a separate permit for herbicide use within the boundaries of the park.

Case Study- Aquatic Herbicides

Lake Setting: Waneta Lake is an 800 acre lake in the western Finger Lakes region that is part of a two-lake chain with Lamoka Lake (downstream to the south); the Waneta-Lamoka Lakes Association was formed in 1938 to address a variety of lake management issues. The lake is also a valued local fishery for largemouth- and smallmouth-bass and a secondary source for muskellunge brood stock throughout the state, and thus the lake fisheries have enjoyed a high level of protection.

The Problem: Waneta Lake has a long history of recreational use impacts associated with both nuisance algae and nuisance weed growth. The latter has been exacerbated by the introduction and spread of Eurasian watermilfoil throughout both Waneta and Lamoka Lakes since at least the mid-1980s. By the late 1990s, Eurasian watermilfoil comprised just over 50% of the biomass of aquatic plants in Waneta Lake. Mechanical weed harvesting was conducted during the mid-1980s, with funds provided through the Aquatic Vegetation Control Program (AVCP, the predecessor to the Finger Lakes-Lake Ontario Watershed Protection Alliance). This was marginally successful, but the funds for this activity dissipated ov

Response: The lake association proposed the use of fluridone to reduce the coverage and density of Eurasian watermilfoil while maintaining sufficient cover of native plants to protect the valuable fisheries resource in both Waneta and Lamoka Lakes. After much discussion and �negotiation�, the NYSDEC issued a permit for the whole-lake application of fluridone only in Waneta Lake at an initial concentration of 12-14 ppb in the summer of 2003, with provisions for a bump application as needed to restore fluridone residuals back to 6ppb within 60 days. Due to very low dilution (probably due to relatively low inflow and low photodegradation), however, fluridone residuals remained above 6ppb, without supplemental applications, for more than 60 days, and remained above 3ppb for nearly 175 days.

Performance standards were devised to evaluate herbicidal impacts to Waneta Lake and proposals for follow-up treatments in Lamoka Lake. Native and exotic plant recovery were monitored as part of an extensive survey program conducted by Cornell University, and results were evaluated by the lake consultant and NYSDEC to determine if �sufficient� recovery existed to maintain cover and refuge in the event of a downstream (Lamoka Lake) treatment. This corresponded to < 25% loss of native plant cover and overall aquatic plant biomass, and > 90% milfoil removal, within the year of treatment, and return to pre-treatment plant densities the following year.

Results: As a result of the herbicide treatment, Eurasian watermilfoil disappeared from the lake, and there was no evidence of milfoil anywhere in the lake through at least the summer of 2004. Traces of native plants were found in 54 of the 91 sites with some evidence of plant growth prior to treatment in 2003, and in 50 sites in 2004, with native plant biomass reduced to about 5% of the pre-treatment native biomass. No significant water quality changes or fisheries impacts were reported (or attributable to the herbicide treatment), and it is expected that native plant recovery will accelerate beginning in 2005, as was found in other lakes with similar initial recovery patterns. Due to delays in the plant recovery in Waneta Lake, however, large-scale treatment of Lamoka Lake was not approved. It is anticipated that the strategies used to evaluate the Waneta Lake treatment will be utilized in assessing the impacts (positive and negative) of other herbicide treatments throughout the state.

Nearly all of the aquatic herbicides registered for use in New York State carry at least one water use restriction, ranging from 24 hour restrictions on bathing to 30 day prohibition of the use of the lake water for irrigation of established row crops. These restrictions are clearly identified on the label governing the use of each of product formulations registered in New York State

Herbicide applicators must also be licensed by New York State. A list of licensed applicators is available from the NYSDEC Bureau of Pesticides in Albany. Applicators may also need to carry an insurance policy.

Permits have been issued for aquatic herbicides in nearly every part of New York StateIn fact, upwards of 500 permits are issued annually, not including purchase permits for small farm ponds. However, in some regions of the state, such as the Adirondacks no aquatic herbicide permits are being issued. The myriad of reasons include overlapping regulatory authority (the NYSDEC and the Adirondack Park Agency), strong sentiments about the use of herbicides, the presence of and concern for protecting rare and endangered species, and the lack of historical precedent in the use of many aquatic plant control strategies (due in part to the historical lack of problems with invasive plants). . A paucity of permits is also the case for lakes in other regions of the state used for potable water intake or encompassing wetland areas, since the permitting rigor is often more significant in these waterbodies. On the other hand, many lakes in the downstate region have been treated with aquatic herbicides.

Copper-based herbicides (for rooted plant control) have been registered for use in New York State, but since they can kill some fish species at the label application rate, these require extensive review and environmental assessment by the NYSDEC.

� History and Case Studies in NYS

Aquatic herbicides have been used in New York State for many years. Federal regulation began by at least the early 1900s, although the �modern� pesticides regulations largely stem from the passage of the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA) in 1947. However, federal and state attention to pesticides, including aquatic herbicides, was significantly heightened by the publication of Silent Spring by Rachael Carson in 1962. Since then the aquatic herbicides used in lakes have been subject to more stringent testing and regulations, resulting in amendments to FIFRA starting in 1972. However, most of the lakes treated with aquatic herbicides have not been closely studied either before or after treatment. The most closely monitored lakes include Waneta Lake in Schuyler County and Snyders Lake in Rensselaer County.

Case Study- Aquatic Herbicides: Waneta Lake (cont)

Lessons Learned: The controversies over the proposedtreatment in Waneta Lake are a microcosm of the issues surrounding the use of aquatic herbicides in New York State, and it is unlikely that all parties involved will agree that the process and the results were adequate. However, the dialogue accompanyiapplication process was insightful and open, and the compromise reached by the advocates for, the opponents of, and the mediators in the permitting and evaluation process may serve as a template for future contentious aquatic plant management proposals. It is also hoped that the results from the well-designed monitoring plan will provide sorely needed answers to continuing questions about the use of aquatic herbicides in Ne

York State lakes

Sources: Lord, P.H., R.L. Johnson, and K. Wagner. 2005. Effective aquatic plant monitoring: data and issues from Waneta Lake. Present

Lord, P.H., R.L. Johnson and M.E. Miller. 2004. Waneta Lake 2003 and 2004 plant community structure researcsubsequent to 2003 fluridone treatment for control of

watermilfoil. Cornell University rep

ENSR International. 2001. Draft supplemental environmental impact statement for the control of Eurasianwatermilfoil in Lamoka and Waneta Lakes wit

� Is That All?

Perhaps no other lake-related issue causes as much heated discussion as chemical controls. At many lake association meeting, large or small, there will likely be two factions, both convinced that the other could ruin the lake. One faction may claim that there are absolutely no conditions or situations that call for chemical treatments. The other group may insist that if herbicides are not applied immediately, weeds will take over the entire lake, destroying recreational use and slicing property values. And neither group is likely to listen to the other.

There have been few, if any, documented cases of an herbicide treatment gone completely awry. Any health problems associated with contact with herbicide-treated lakes may be perceived and based on an expected threat. While toxicological studies indicate that short-term human health effects or impacts to non-targeted organisms in the lake ecosystem are probably very small when herbicides are applied according to the permitted label, long-term monitoring of ecological or human health has not occurred. An herbicide treatment may also be ineffective due to poorly timed applications, unusual weather conditions, eradication of non- target plants, reinfestation by exotic species, or by simply using the wrong herbicide to control a particular species. Even when successful, treatments will have to be repeated at least every growing season, as is the case with nearly all symptom- based vegetation control techniques. These limitations and concerns need to be balanced against the ecological damage that may occur when invasive plants spread through a lake ecosystem, creating �biological pollution� and drastically altering the ecological balance.

Although herbicide use requires a permit in New York State, the decision whether to use chemical treatment usually rests with the lake association, residents, or lake management team. As much information as possible should be obtained about the particular species of nuisance plant, proposed herbicide, existing water chemistry conditions on the lake, and the benefits and drawbacks of using this particular herbicide on this particular lake to control this particular plant. It is important to use discretion when extrapolating information from a different lake to the conditions at your lake. Differing weather conditions, recreational uses, water chemistry characteristics, and vegetation types could yield dramatically different results from one lake to another. The DEC regional office may be able to provide some assistance in obtaining information about the lake and proposed herbicide.