Pesticides compound climate risk to reef
Corals already under pressure from global climate change are facing an additional threat in the form of pesticides running off from the land, shows a new scientific study published in the journal Marine Ecology Progress Series.
Corals can be harmed by agricultural chemicals at levels so low as to be practically undetectable, a ground-breaking study by scientists at the Australian Institute of Marine Science (AIMS), the ARC Centre of Excellence for Reef Studies (ARC CoE) and James Cook University (JCU) concludes.
Reefs on a global scale are under threat from many sources; one of the most insidious is land based pollutants from agriculture – and the new research indicates that this threat may have been underestimated.
The study measured the sensitivity of the eggs, larvae and adults of the broadcast spawning coral, Acropora millepora, to a number of common pollutants including four classes of agricultural insecticides and a fungicide commonly used in Great Barrier Reef river catchments.
According to AIMS scientist, Dr Andrew Negri the novelty of the study is that it explored the effects of insecticides on many different life stages of the coral.
Normally developing coral embryos at the “prawn chip” stage, 12 hours after fertilisation. Image: Andrew Negri
“Previous studies have focused only on the adults, which seem more robust to insecticides. Our study looked at fertilization, larval development, survival and metamorphosis and we found that some of these stages were very vulnerable to these chemicals at very low concentrations”.
Coral embryos exposed to 1 µg/L of the fungicide MEMC. The embryos have not developed normally and will not make it to the larval stage. Image: Andrew Negri
Kathryn Markey, of JCU, continues “Neither fertilization rates nor adult branches were affected by any of the insecticides. In contrast, coral settlement was reduced by between 50 and 100% following 18 hours exposure to very low concentrations of each insecticide”.
Dr Andrew Baird of the ARC CoE for Reef Studies says “These developmental stages and events are critical points in the life history of corals. The failure of any one of these events could seriously reduce the ability of coral populations to replenish themselves”.
Close up image of a coral branch exposed to 1 µg/L of the fungicide MEMC. The brown tissue is normal but the MEMC has caused tissue death, exposing the white skeleton underneath.
Image: Andrew Negri
In addition, the study found that coral at all life stages was particularly sensitive to the agricultural fungicide MEMC, which caused bleaching in adult corals at levels so low as to be scarcely measurable.
These are some of the most sensitive biological responses to pesticide contamination in the marine environment yet demonstrated. The researchers say the real worry is that the effects of these chemicalswere found at such low levels. In addition, the high sensitivity of coral settlement also suggests current water quality guidelines may not adequately protect all coral life stages.
The team says that both state and federal governments have recognised the pesticide threat to the Great Barrier Reef where up to 80 per cent of the catchment contains some form of agriculture.
The Great Barrier Reef Marine Park Authority, with other government agencies, is currently overseeing the implementation of the “Reef Water Quality Protection Plan”, a ten-year $40 million program to halt and reverse the declining quality of water entering the GBR Marine Park by improving land management practices.
However such measures do not necessarily apply elsewhere in the world.
Dr Negri says that the latest IPCC climate change report provides a particular context and reasons for concern about the impact of pesticides on corals: “Corals are already under pressure from rising sea temperatures and pesticides in runoff may be causing additional critical stresses on corals especially during the early life histories such as the larval phase,” he says.
*This story was jointly released by AIMS and the Australian Research Council Centre of Excellence for Coral Reef Studies.
THIS STUDY FROM JAMA AND SHOWN IN THE WEBMD MAGAZINE IS STUNNING. TO SEE, CLICK BELOW:
J. Aquat. Plant Manage.
Efﬁcacy of Fluridone, Penoxsulam, and Bispyribac-sodium on Variable-leaf Milfoil
LEEANN M. GLOMSKI
AND MICHAEL D. NETHERLAND
Variable-leaf milfoil (
Michx.) is a native perennial submersed plant ranging from southwestern Quebec and Ontario to North Dakota and southward to New Mexico and Florida (Godfrey and Wooten 1981). It is classiﬁed as a species of concern in Kentucky and is endangered in Ohio and Pennsylvania (USDA 2007). In the northeastern United States, however, variable-leaf milfoil is not native and is considered an invasive and weedy species. Variable-leaf milfoil is listed as invasive in states such as Connecticut and Maine, prohibited in Massachusetts and New Hampshire, and is a class A noxious weed in Vermont (NHDES 2007, USDA 2007). As an invasive milfoil, it causes many of the same problems as Eurasian watermilfoil (
L.), including shading out native submersed vegetation and interfering with recreational activities and water supplies (NH-DES 2002, Halstead et al. 2003). Variable-leaf milfoil has been estimated to reduce lakefront property values by as much as 20 to 40 percent in New Hampshire (Halstead et al. 2003). Variable-leaf milfoil has been described as an aggressive invader that can grow up to one inch per day under optimal nutrient, temperature, and light conditions and spreads mainly via fragmentation (NH-DES 2002). To date, the auxin-type herbicides are considered the most effective at controlling variable-leaf milfoil. Research by Getsinger et al. (2003) found that triclopyr (3,5,6-trichloro-2pyridinyloxyacetic acid) was effective at controlling variableleaf milfoil over a wide range of rates and exposure times. Bugbee et al. (2003) reported good control of variable-leaf milfoil treated with 2,4-D ester [(2,4-dichlorophenoxy)acetic acid] in the ﬁeld. Although effective, both triclopyr and 2,4D have use restrictions for drinking water and therefore may not be a viable option for treatment around potable water intakes. Possible alternatives for controlling variable-leaf milfoil in large-scale situations where triclopyr and 2,4-D cannot be used include the herbicide ﬂuridone and the new acetolactate synthesis (ALS) inhibitors bispyribac-sodium and penoxsulam. The use and impacts of ﬂuridone for whole-lake management of Eurasian watermilfoil has been addressed by several researchers (Smith and Pullman 1997, Madsen et al. 2002, Bremigan et al. 2005); however, information is limited regarding the efﬁcacy of ﬂuridone on variable-leaf milfoil.
Moreover, aside from laboratory scale studies with the ALS inhibitor bensulfuron methyl (Nelson et al. 1993) on Eurasian watermilfoil, there is no published laboratory or ﬁeld information on ALS inhibitors for either Eurasian or variable-leaf milfoil. Fluridone has been registered by the U.S. Environmental Protection Agency (USEPA) for aquatic use for more than 30 years, while penoxsulam was registered by the USEPA for aquatic use in 2007. Bispyribac-sodium is still being evaluated for aquatic use under an Experimental Use Permit (EUP). Like ﬂuridone, the ALS inhibitors target a plant-speciﬁc enzyme; thus, at proposed use rates they have very low toxicity to mammals, ﬁsh, and invertebrates (WSSA 2007). As such, these favorable toxicology proﬁles will likely preclude consumptive restrictions on water use. Fluridone inhibits the plant enzyme phytoene desaturase (PDS) in the carotenoid biosynthetic pathway. Carotenoids play an important role in preventing photooxidative damage by quenching chlorophyll triplets that would lead to oxygen singlets (Bartley and Scolnik 1995). Without carotenoids, new plant tissue becomes bleached due to photodestruction of chlorophyll (Bartels and Watson 1978). Bispyribac-sodium and penoxsulam inhibit the plant enzyme acetolactate synthase (ALS), which is involved in biosynthesis of the branched-chain amino acids. The ALS compounds inhibit the production of the amino acids valine, leucine, and isoleucine in plants by binding to the ALS enzyme (Tranel and Wright 2002). Without these amino acids, protein synthesis and growth are inhibited, ultimately causing plant death (WSSA 2007). The impact of these slow acting enzyme inhibitors on plants such as hydrilla (
[L.f.] Royle) and Eurasian watermilfoil is most notable on the actively growing shoot meristems, and extended exposures (60 to 120 days) to both PDS and ALS inhibitors are likely required to achieve plant control (Langeland 1993, Nelson et al. 1993, Netherland et al. 1993, 1997, Netherland and Getsinger 1995). Our objective was to determine the efﬁcacy of ﬂuridone, bispyribac-sodium, and penoxsulam on variable-leaf milfoil.
MATERIALS AND METHODS
This study was initiated on March 9, 2006, in the greenhouse at the U.S. Army Engineer Research and Development Center’s Lewisville Aquatic Ecosystem Research Facility (LAERF) in Lewisville, Texas. Plastic pots (750 ml) were ﬁlled with LAERF pond sediment amended with 3 g L
U.S. Army Engineer Research and Development Center, Lewisville Aquatic Ecosystem Research Facility, 201 E. Jones St., Lewisville, TX 75057; e-mail: LeeAnn.M.Glomski@usace.army.mil.
U.S. Army Engineer Research and Development Center, 3909 Halls Ferry Rd., Vicksburg, MS 39180. Received for publication July 22, 2007 and in revised form June 16, 2008.
J. Aquat. Plant Manage.
mocote (16-8-12). Each pot was planted with two 15-cm apical tips of variable-leaf milfoil. Pots were topped with a 1-cm layer of play sand, and two pots were placed in each aquarium. Aquaria were ﬁlled with alum-treated Lake Lewisville water. Eight aquaria were situated into each of eight 1000-L ﬁberglass tanks ﬁlled with water. Water temperatures were maintained at 22 to 24 C. Carbon dioxide was bubbled into each aquarium once a day to reduce pH (6.5 to 7.0) for improved plant growth. Ten days after plants were established, aquaria were treated with one of the following herbicides: bispyribac-sodium, ﬂuridone, or penoxsulam. Treatment rates included 5, 10, and 20 µg ai L
. The treatment rates evaluated were chosen based on current proposed use rates for the submersed use of ALS inhibitors and current recommended use rates for ﬂuridone. After treatment, herbicides were left in the aquaria for a static exposure. At 42 days after treatment (DAT) all viable shoot biomass was harvested, dried at 65 C, and weighed. Dry weight values for bispyribac-sodium, ﬂuridone, and penoxsulam were transformed by squaring the data to meet the assumptions of normality and equal variance. Data were subjected to oneway analysis of variance (ANOVA) and means were compared via the Student-Newman-Keuls Method (SNK; P
This study was set-up in the same manner as study 1; however, four pots of variable-leaf milfoil were planted in each aquarium on 13 July 2006. Ten days after planting, aquaria were treated with one of the following herbicides: bispyribacsodium, ﬂuridone, or penoxsulam. Rates of ﬂuridone and penoxsulam were 2.5, 5, 10, 20, and 50 µg ai L
; bispyribacsodium rates were 20 and 50 µg ai L
. Treatments were randomly assigned and replicated 4 times. At 50 DAT all viable shoot biomass was harvested, dried at 65 C and weighed. Bispyribac-sodium data was square root transformed to meet the assumptions of normality and equal variance. The data were subjected to analysis of variance (ANOVA). Means were compared using the Student-Newman-Keuls Method (SNK; P = 0.169). Based on evidence of a dose response, ﬂuridone, and penoxsulam data were subjected to regression analysis.
RESULTS AND DISCUSSION
Both ﬂuridone and penoxsulam were active on variableleaf milfoil, while bispyribac-sodium treatments showed limited activity at the use rates tested (Figure 1). Plants treated at 50 µg ai L
bispyribac-sodium in study 2 (data not shown) did not reach the water surface and showed increased production of lateral meristems and slight curling of apical tips at the time of harvest. A static exposure to bispyribac-sodium at 50 µg ai L
resulted in no biomass reduction compared to control, and effects were described as growth regulating. Penoxsulam and ﬂuridone were much more active against variable-leaf milfoil (Figures 1 and 2). The effect of penoxsulam and ﬂuridone on variable-leaf milfoil (Figure 2A and 2B) can be described as exponentially curved. The lowest
rate of each herbicide (2.5 µg ai L
) reduced biomass by about 27%. Fluridone at 5 µg ai L
reduced variable-leaf milfoil biomass by 75 and 87% in both studies; rates higher than 5 µg ai L
did not improve control. Fluridone symptoms appeared sooner in plants treated at the higher use rates, but by the time of harvest all treatments were similar. This lack of an improved response to increasing use rates of ﬂuridone has also been described for Eurasian watermilfoil and hydrilla (Netherland and Getsinger 1995). Penoxsulam controlled variable-leaf milfoil by 27 to 91% in both studies, and control increased as use rates increased up to 20 µg ai L
. There was no difference noted in the efﬁcacy of the 20 and 50 µg ai L
treatments. Variable-leaf milfoil treated at 2.5 µg ai L
had grown to the water surface, whereas plants treated at 5 µg ai L
were vibrant and six inches below the water surface at the time of harvest. Plants treated at 10 and 20 µg ai L
had collapsed in the water column one week prior to harvest and started to decompose. Plants treated at 50 µg ai L
penoxsulam had little to no new growth after treatment and were starting to decompose at the time of harvest. Of the herbicides tested only ﬂuridone and penoxsulam showed potential for controlling variable-leaf milfoil at concentrations currently labeled or proposed for EUP aquatic labels. While these laboratory results suggest that variable-leaf milfoil is quite sensitive to low use rates of ﬂuridone, reports from aquatic plant managers suggest that ﬂuridone has provided inconsistent operational control of variable-leaf milfoil in the ﬁeld. Prior ﬂuridone studies in outdoor mesocosms have demonstrated that treatment timing is crucial for some ﬂuridone-sensitive species such as elodea (
Michx.), while treatment timing had much less impact on Eurasian watermilfoil (Netherland et al. 1997). Our laboratory studies suggest that plants like variable-leaf milfoil, elodea,
Figure 1. Mean (±SE) dry weight biomass (g) of variable-leaf milfoil biomass 42 days after treatment with bispyribac-sodium, ﬂuridone, and penoxsulam in study 1. Each bar represents the average of four replicate treatments. Bars sharing the same letter do not signiﬁcantly differ from each other. Data was subjected to a one-way analysis of variance, and means were separated using the Student-Newman-Keuls Method (SNK; P ≤ 0.001).
J. Aquat. Plant Manage.
46: 2008. 195
Brazilian elodea (
Planch.), and cabomba (
A. Gray) can quickly grow to the water surface; however, once at the surface growth rates slow dramatically, and these plants do not form dense entangled canopies similar to Eurasian watermilfoil and hydrilla. Treatment with ﬂuridone or ALS inhibitors when growth rates have decreased would result in reduced symptoms and less stress on the plant. The current laboratory data would suggest that early treatment of actively growing variable-leaf milfoil with ﬂuridone or penoxsulam may allow for lower use rates than treatments conducted later in the season. While penoxsulam was much more active than bispyribacsodium, this difference in sensitivity to two different ALS inhibitors is not unexpected. Despite impacting a similar enzyme, ALS inhibitors show a surprising range of plant selectivity (WSSA 2007). Slight changes in the molecular structure of ALS-inhibiting herbicides greatly affect the potency and weed spectrum (Ladner 1991, Ren et al. 2000). The proliferation of ALS compounds in terrestrial agriculture has yielded several potential candidates for the aquatic market, and the differences in use patterns and selectivity in
the terrestrial market suggest that we need to carefully evaluate the efﬁcacy and selectivity of these ALS compounds. While variable milfoil is an aggressive target plant in the northeastern United States, it is often regarded as a valuable plant throughout its native range. In many cases, aquatic managers need information on both the proposed efﬁcacy as well as the selectivity of a given compound (Koschnick et al. 2007). The information generated from these studies provides both efﬁcacy and potential selectivity information for variable-leaf milfoil.
The authors would like to thank Kristin Dunbar for her assistance during this study and Angela Poovey and Gary Dick for early reviews of this article. Permission was granted by the Chief of Engineers to publish this information. Citation of trade names does not constitute an ofﬁcial endorsement or approval of the use of such commercial products.
Bartels, P. G. and C. W. Watson. 1978. Inhibition of carotenoid synthesis by ﬂuridone and norﬂurazon. Weed Sci. 26:198-203. Bartley, G. E. and P. A. Scolnik. 1995. Plant carotenoids: Pigments for photoprotection, visual attraction and human health. Plant Cell 7:1027-1038. Bugbee, G. J., J. C. White and W. J. Krol. 2003. Control of variable watermilfoil in Bashan Lake, CT with 2,4-D: Monitoring of lake and well water. J. Aquat. Plant Manage. 41:18-25. Bremigan, M. T., S. M. Hanson, P. A. Soranno, K. S. Cheruvelil and R. D. Valley. 2005. Aquatic vegetation, largemouth bass and water quality responses to low-dose ﬂuridone two years post treatment. J. Aquat. Plant. Manage. 43:6575. Getsinger, K. D., S. L. Sprecher and A. P. Smagula. 2003. Effects of triclopyr on variable-leaf milfoil. J. Aquat. Plant Manage. 41:124-126. Godfrey, R. K. and J. W. Wooten. 1981. Aquatic and Wetland Plants of Southeastern United States: Dicotyledons. Univ. Georgia Press, Athens, GA. 933 pp. Halstead, J. M., J. Michaud, S. Hallas-Burt and J. P. Gibbs. 2003. Hedonic analysis of effects of a nonnative invader (
) on New Hampshire (USA) lakefront properties. Environ. Manage. 32:391-398. Koschnick, T. J., M. D. Netherland and W. T. Haller. 2007. Effects of three ALSinhibitors on ﬁve emergent native plant species in Florida. J. Aquat. Plant Manage. 45:47-51. Ladner, D. W. 1991. Structure-activity relationships among imidazolinones herbicides, pp. 31-51.
: The Imidazolinone Herbicides. D. L. Shaner and S. L. O’Connor (eds.). CRC Press. Langeland, K. A. 1993. Hydrilla response to Mariner applied to Lakes. J. Aquat. Plant Manage. 31:175-178. Madsen, J. D., K. D. Getsinger, R. M. Stewart and C. O. Owens. 2002. Whole Lake ﬂuridone treatments for selective control of Eurasian watermilfoil: II. impacts on submersed plant communities. Lake Reserv. Manage. 18:191200. Nelson, L. S., M. D. Netherland and K. D. Getsinger. 1993. Bensulfuron methyl activity on Eurasian watermilfoil. J. Aquat. Plant Manage. 31:179-185. Netherland, M. D., K. D. Getsinger and E. G. Turner. 1993. Fluridone concentration and exposure time requirements for control of Eurasian watermilfoil and hydrilla. J. Aquat. Plant Manage. 31:189-195. Netherland, M. D. and K. D. Getsinger. 1995. Laboratory evaluation of threshold ﬂuridone concentrations under static conditions for controlling hydrilla and Eurasian watermilfoil. J. Aquat. Plant Manage. 33:33-36. Netherland, M. D. K. D. Getsinger and J. D. Skogerboe. 1997. Mesocosm evaluation of the species selective potential of ﬂuridone. J. Aquat. Plant Manage. 35:41-50. NH-DES (New Hamphire Department of Environmental Sciences). 2002. Variable Milfoil. Environmental fact sheet WD-BB-23. NH-DES (New Hamphire Department of Environmental Sciences). 2007. Law prohibits exotic, aquatic plants. Environmental fact sheet WD-BB-40.
Figure 2. Dry weight biomass (g) of variable-leaf milfoil 50 days after treatment with (A) ﬂuridone and (B) penoxsulam in study 2. Data were subjected to regression analysis.
J. Aquat. Plant Manage.
Ren, T. R., H. W. Yang, X. Gao, X. L. Yang and J. J. Zhou. 2000. Design, synthesis and structure-activity relationships of novel ALS-inhibitors. Pest Manage. Sci. 56:218-226. Smith, C. S. and G. D. Pullman. 1997. Experience using Sonar® A.S. aquatic herbicide in Michigan. Lake Reserv. Manage. 13:338-346. Tranel, P. J. and T. R. Wright. 2002. Resistance of weeds to ALS-inhibiting herbicides: what have we learned? Weed Sci. 50:700-712.
AS YOU CAN SEE, THERE ARE IMPORTANT ISSUES WHEN USING FLURIDONE FOR INVASIVE PLANT CONTROL.
Eutrophication and Aquatic Plant
Fluridone is a systemic herbicide introduced in 1979 (Arnold 1979) and in widespread use since the mid-1980’ s, although some states have been slow to approve its use. Fluridone currently comes in two formulations, an aq ueous suspension and a slow release pellet, although several forms of pellets are now on the market. This chemical inhibits carotene synthesis, which in turn exposes the chlorophyll to photodegradation (Gangstad, 1986; Langeland, 1993). Most plants are negatively sensitive to sunlight in the absence of protective carotenes, resulting in chlorosis of tissue and death of the entire plant with prolonged exposure to a sufficient concentration of
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4.0 Methods to Control Aquatic Plants Page 4-114
fluridone. When carotene is absent the plant is unable to produce the carbohydrates necessary to sustain life (Eshenroeder, 1989). Some plants, including Eurasian watermilfoil, are more sensitive to fluridone than others, allowing selective control at low doses.
For susceptible plants, lethal effects are expressed slowly in response to treatment with fluridone. Existing carotenes must degrade and chlorosis must set in before plants die off; this takes several weeks to several months, with 30-90 days given as the observed range of time for die off to occur after treatment. Fluridone concentrations should be maintained in the lethal range for the target species for at least 6 weeks and preferably 9 weeks. This presents some difficulty for treatment in areas of substantial water exchange.
Fluridone is considered to have low toxicity to invertebrates, fish, other aquatic wildlife, and humans. The USEPA has set a tolerance limit of 0.15 ppm for fluridone or its degradation products in potable water supplies, although some state restrictions are sometimes lower. Control of Eurasian watermilfoil has been achieved for at least a year without significant impact on non-target species at doses <0.01 mg/L (Netherland et al., 1997; Smith and Pullman, 1997). The slow rate of plant die-off minimizes the risk of oxygen depletion.
If the recommended 40-60 days of contact time can be achieved, the use of the liquid formulation of fluridone in a single treatment has been very effective. Where dilution is potentially significant, the slow release pellet form of fluridone has generally been the formulation of choice. Gradual release of fluridone, which is 5% of pellet content, can yield a relatively stable concentration. However, pellets have been less effective in areas with highly organic, loose sediments than over sandy or otherwise firm substrates (Haller, Univ. FL, pers. comm., 1996). A phenomenon termed “plugging” has been observed, resulting in a failure of the active ingredient to be released from the pellet. While some success in soft sediment areas has been achieved (ACT, 1994; Bugbee and White, 2002), pellets may be less efficient than multiple, sequential treatments with the liquid formulation in areas with extremely soft sediments and significant flushing. It may also be possible to sequester a target area with limno-curtains to reduce dilution effects in the target area (T. McNabb, AquaTechnex, pers. comm., 2001; G. Smith, ACT, pers. comm., 2002; L. Lyman, Lycott, pers. comm., 2002b).
18.104.22.168 Effectiveness of Fluridone
Fluridone is the active ingredient in the registered herbicide Sonar and also in the newer competitor product, Avast, both of which have liquid and pelletized formulations Fluridone can be a broad spectrum herbicide when applied at full label recommendations (Pullman, 1994). In most cases, however, fluridone is used as a selective herbicide. For example, treating Myriophyl l um spi c atum (Eurasian watermilfoil) or Potamogeton c rispus (curly leaf pondweed) at a low dose (0.005-0.010 mg/L) may have little impact on surrounding vegetation (Pullman, 1994; Harman, 1995; Langeland, 1993; Getsinger et al., 2000). Application rates recommended for control of non-native species such as Eurasian watermilfoil and curly leaf pondweed range from 0.007 to 0.015 ppm for a whole lake treatment (Pullman, 1994), although even lower doses have been tried with some success.
The selectivity of fluridone for the target species depends on the timing and the rate of application (G. Smith, ACT, pers. comm., 1995; Harman, 1995). Early treatment (April/early
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4.0 Methods to Control Aquatic Plants Page 4-115
May) with fluridone effectively controls overwintering perennials before some of the beneficial species of pondweed and naiad begin to grow (G. Smith, ACT, pers. comm., 1995). Additionally, M. spicatum begins growing earlier in the season than many native plants (Smith and Barko, 1990) and is thus susceptible to an early season treatment while native species are still dormant (Harman, 1995). For a complete list of plants that can be controlled by fluridone see Table 4-5 and Appendix III.
Experience with fluridone since 1995 has included a wide range of treatments at more dosages, and the susceptibility and tolerance of many species has been determined. Variability in response has also been observed as a function of dose, with lower doses causing less impact on non-target species. However, lesser impact on target plants has also been noted in some cases, so dose selection involves balancing risk of failure to control target plants with risk of impact to non-target species.
Eurasian watermilfoil has been reduced with fluridone at average concentrations as low as 4 ppb in whole lake treatments for at least a year, and doses above 20 ppb appear unnecessary as long as dilution is not a serious influence (Pullman, 1993; Netherland et al., 1997; Smith and Pullman, 1997). As fluridone works slowly, it is essential that an adequate concentration be maintained for multiple weeks. This presents a challenge to application where dilution effects are appreciable, but multiple approaches have been developed to enhance effectiveness. Many native species will survive these doses, which are well below the maximum of 50 ppb (liquid form) or 150 ppb (pellet form) set for use in Massachusetts waters. Additionally, seeds are unaffected, and many of the desirable native species are seed-producing annuals. Such annuals include the highly desirable macroalgae Chara and Nitella, carpet forming species of Naj as, and nearly all desirable Potamogeton species.
Multiple low dose treatments with fluridone have been successfully applied to whole lakes in an effort to minimize the effects on the native plant assemblage. An outdoor mesocosm evaluation concluded that fluridone concentrations between 5 and 10 ppb (residues remaining above 2 ppb) for an exposure period of >60 days effectively controlled Eurasian watermilfoil during the year of treatment while minimally affecting non-target species such as E lodea canadensis, Potamogeton nodosus, P. pectinatus and Vallisneria americana (Netherland et al. 1997). Data from Michigan provided in Getsinger 2001 suggest that many species do respond differently to fluridone at different doses, and that response may vary the year after treatment as well. The response of species the year after treatment at <6 ppb was variable but not extreme; no species remained in consistent decline, indicating recovery of many susceptible populations. However, this also applies to Eurasian watermilfoil, which showed signs of resurgence in a significant number of cases where the dose was <6 ppb.
Experience in Vermont (G. Garrison and H. Crosson, VTDEC, pers. comm., 2001) with low dose treatments indicates that recovery of Eurasian watermilfoil was substantial the year after treatment with an average of 6 ppb (range = 2 to 11 ppb over 6 weeks). A fluridone assay was used to track concentrations to the nearest 0.5 ppb. There was minimal damage to non-target flora, but relief from Eurasian watermilfoil infestation may be short-lived for a substantial cost. Use of the low dose was driven by concerns by the fishery agency in VT over loss of vegetative cover in the year of treatment.
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By comparison, a 12 ppb treatment of Snyders Lake in New York (S. Kishbaugh and J. Sutherland, NYSDEC, pers. comm., 2002) with one booster treatment to raise the concentration back to near 12 ppb after a month resulted in near eradication of Eurasian watermilfoil and restoration of a highly desirable native community, based on four years of monitoring. Damage to some non-target species was indeed observed in the year of treatment, but substantial recovery of native species was observed the same year. Both an increase in taxonomic richness and expansion of coverage were observed during the year after treatment. Subsequent plant community changes have been more subtle, and hand harvesting of sporadic Eurasian watermilfoil stems has maintained control.
Fluridone is also applied for the control of fanwort (Cab omb a caroliniana), but typically at higher doses that used for Eurasian watermilfoil control (G. Bugbee and J. White, CT Agric. Exper. Station, pers. comm., 2002; G. Smith, ACT, pers. comm., 2002, L. Lyman, Lycott, pers. comm., 2002b). Doses >10 ppb are almost always applied for fanwort control, with doses of 1215 ppb showing signs of success and doses near 20 ppb providing nearly complete fanwort kill. Unfortunately, at doses approaching 20 ppb, nearly all other submergent vegetation will be impacted as well.
22.214.171.124 Specific ShortTerm Impacts on NonTarg et Org anisms by Fluridone
Maximum label application rates are 8 lb per acre-foot and 0.4 quarts per acre foot for the Sonar SRP and Sonar AS formulations, respectively. The maximum concentrations of fluridone expected would be 0.15 ppm, but since the mid-1990s it has been extremely rare to have a target concentration greater than 0.02 ppm. With target levels as low a 0.006 ppm, impacts on the target species are not always achieved, and only the most sensitive non-target vegetation (e.g., water marigold, Megalodonta b eck ii) is impacted. At application rates more certain to kill milfoil, partial damage to many non-target plants has been observed, but recovery within 1-2 years is typical.
Research on degradation products of fluridone initially suggested some possible effects, but further testing indicated no significant threat. The potential formation of N-methylformamide (NMF), a compound that is toxic to humans, was investigated in field experiments by Smith et al. (1991) in Uxbridge and Grafton, Massachusetts, after it was observed as a breakdown product of fluridone in laboratory experiments. Their findings agreed with the results of a similar study by Osborne et al. (1989), in that no NMF was detected in the field. The laboratory experiments were conducted in the absence of aquatic plants and sediments. The contrasting results suggest that either fluridone behaves differently in the laboratory than it does in the field or that NMF is broken down rapidly in natural aquatic environments (Smith et al., 1991).
Substantial bioaccumulation has been noted in certain plant species, but not to any great extent in animals. The USEPA has designated a tolerance level of 0.5 ppm (mg/L or mg/kg) for fluridone residues or those of its degradation products in fish or crayfish. The LC50 for sensitive fish species (excluding walleye, which is not common in the state) is 7.6 ppm (Paul et al., 1994), which is 50 times higher than the expected maximum concentrations and about 500 times higher
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4.0 Methods to Control Aquatic Plants Page 4-117
than typical doses used today. Other studies report LC50s as high as 22 ppm (Westerdahl and Getsinger, 1988), but generally there is little variation from species to species.
Fluridone was not found to impact non-target organisms at concentrations of 0.1 to 1.0 ppm in contained field experiments. Mosquitofish (Gambusia af f inis) were added to each container to evaluate the impacts of fluridone on the fish at concentrations of 4.0, 2.0, 1.0, 0.5 and 0.25 ppm. G. af f inis survived and reproduced at all concentration levels. Additionally, fluridone did not accumulate in the fish tested. The fluridone level in pumpkinseed (Lepomis gibbosus) detected 7 days after an application of 0.1 ppm was 0.023 ppm. No detectable residue was found in L . gibbosus 27 days after application. Other non-target organisms present included bluegills, catfish, crayfish, frogs and water snakes. No adverse impacts to these organisms were observed (McCowen et al., 1979).
Fluridone has a low order of toxicity to mammals. Rat LD50s are >10,000 mg/kg (Appendix III).
126.96.36.199 Specific Long-Term Impacts on Non-Target Organisms by Fluridone
Fluridone has not been identified as a carcinogen or mutagen. A “No Observed Effects Level” for teratogenic effects for fluridone is greater than 100 mg/kg/day (see appendix III for further toxicity information). Long-term negative impacts to non-target organisms are not expected from the use of fluridone. To the contrary, Schneider (2000) found that fluridone use at low doses in Michigan lakes resulted in improved fishery conditions, but not all species have been studied and a long-term loss of vegetation could be expected to alter the fish community.
188.8.131.52 Specific Short-Term Impacts on Water Quality by Fluridone
Fluridone did not affect water quality in contained field experiments. The parameters measured included pH, BOD, color, dissolved solids, hardness, nitrate nitrogen, total phosphorus and turbidity (McCowen et al., 1979; Arnold, 1979). The slow die-off of plants susceptible to fluridone minimizes the potential for any water quality impacts.
Fluridone should not be applied within 1/4 mile of a potable water intake at levels greater than 0.02 ppm. Water treated with fluridone should not be used for irrigation for 7 to 30 days (irrigation restrictions vary depending on the size of the lake or pond, type of vegetation to be irrigated and which form of the product is used). Federal and Massachusetts registered Sonar labels do not include restrictions for swimming and fishing (SePRO, 1994a; 1994b). However, labels for use in New York prohibit swimming for 24 hours after application (Harman, 1995). Because this product has a relatively long environmental half-life and is not readily sorbed to the sediments, it has a greater tendency to disperse from the treated area than other herbicides. However, the apparent lack of impact on non-target fauna has allowed use of this herbicide in places where others are prohibited, and dispersion is more an issue for treatment effectiveness than impacts on water quality.
Eutrophication and Aquatic Plant Management in Massachusetts
4.0 Methods to Control Aquatic Plants Page 4-118
184.108.40.206 Specific Long-Term Impact on Water Quality by Fluridone
The degradation of fluridone is dependent on sunlight and temperature. The half-life of fluridone in Pout Pond, Uxbridge, Massachusetts was 40 days, but fluridone was more persistent in winter than in summer (Smith et al., 1991). Half-life values as short as 20 days have been recorded.
220.127.116.11 Implementation Guidance for Fluridone
Adhere to all label restrictions. Licensed professionals must perform the treatments. Most treatments with fluridone are conducted in the spring, when target plants are most actively growing. Treatment could occur as early as late March, with an early ice-out, with booster treatments occurring several weeks after as needed in order to maintain the desired average concentration for 40-60 days. The physiological advantage of this time period is sometimes offset by the logistical disadvantage of higher flows and dilution effects during spring. In some cases, treatment has been postponed until summer or even autumn to minimize the volume of water that must be treated. Some successes have been achieved in this manner (Burns, SePRO, pers. comm., 2001), but it has also been suggested that residues remaining until the next spring are an important cause of target plant decline.
Starting at a lower dose (<0.02 ppm) and tracking the concentration has been made possible by immunoassay technology. This allows the herbicide concentration to be “bumped” or “boosted” as needed if dilution and degradation are substantial, while minimizing herbicide use and associated costs and possible unwanted impacts (Getsinger et al., 2002; Madsen et al., 2002). The level of sophistication achieved with fluridone has moved herbicide treatments into a new era, with flexible applications and considerable creativity on the part of experienced applicators. Licensed professionals must perform the treatments.
Holding the chemical within a target area smaller than the lake remains a challenge, but progress has been made there as well. Sequestered treatments were conducted in 2000 in a Washington lake (T. McNabb, AquaTechnex, pers. comm., 2001), in which a 20 acre area and a 5 acre area impacted by Eurasian watermilfoil were surrounded with an impermeable barrier and treated with fluridone at 0.01-0.03 ppm. Follow-up monitoring has indicated success through 2002. Dilution and degradation of fluridone were still factors, but much less so than for partial lake treatments or whole lake treatments where flushing is high. A higher initial concentration of fluridone is normally used (>20 ppb) in such treatments to ensure that the milfoil is killed. It is assumed that nearby native plants will colonize the area once the milfoil is gone.
A treatment in Connecticut for Eurasian watermilfoil (G. Smith, ACT, pers. comm., 2002) and another in Massachusetts for fanwort (L. Lyman, Lycott, pers. comm., 2002b) applied limnocurtains to sequester a section of each lake. In these cases, the lakes had hourglass shapes, making division of the lake at the isthmus much simpler than attempting to isolate major portions of a lake without such a constriction. Both treatments appear to have been successful through the year of treatment, with doses of 0.006 (CT) to 0.012 (MA) ppm.
Fluridone is still sometimes used for partial lake treatments without sequestration, but the risk of failure is higher. At issue are the high diffusion and dilution factors for fluridone, which reduce the concentration in the target area in most cases. Usually a pelletized form of fluridone is used
Eutrophication and Aquatic Plant Management in Massachusetts
4.0 Methods to Control Aquatic Plants Page 4-119
for such treatments, providing gradual release of fluridone into the target area to offset diffusion and dilution. Results have been quite variable. Application to two 100-acre plots in Saratoga Lake in 2000 provided minimal relief from milfoil in the year of treatment and only limited effects in 2001 (G. Smith, ACT, pers. comm., 2001). Treatment of a 5 acre cove in a lake in CT with Sonar SRP in 2000 (Bugbee and White, CT Ag. Exp. Station, pers. comm., 2002) showed no effects for 60 days after treatment, but provided a complete kill of target plants by 90 days after treatment. Newer pellet formulations (Sonar PR or Sonar Q) may improve predictability of such treatments. However, increased cost and continued dilution impacts remain impediments to application. Re-infestation from untreated areas may quickly ameliorate whatever benefits are realized, and
DNR WARY OF FLURIDONE TO CLEAR LAKES OF WEEDS
Ron Seely Wisconsin State Journal Jul 22, 2005
Experts with the Department of Natural Resources say research shows the use of a chemical called fluridone to treat weed-choked Madison lakes could cause more problems than it solves.
Some Madison-area residents are so fed up with the thick weeds and algae this summer that they are petitioning the DNR to try fluridone.
The petition drive was prompted by a Wisconsin State Journal column by Susan Lampert Smith about a lake in Michigan that was treated with the chemical. Fluridone cleared up problem weeds in Houghton Lake within six weeks of its use, though some watermilfoil returned and required spot treatment.
Lake residents told Smith the chemical treatment didn’t harm fish or cause an algae bloom as some had predicted.
Mary Lawson, who has lived on Lake Mendota for years, said she started circulating the petition because lake weeds have made life on the lake miserable.
“We used to be able to enjoy the lake most of the summer,” Lawson said. “But over the last ten years it has really started to deteriorate. We get in and pull the weeds and wheelbarrow them out. Last July Fourth we pulled weeds for four hours and the next night a whole new batch blew in. We can’t even invite friends over any more because it smells so bad.”
Lawson said she has probably collected 50 or 60 signatures and hopes to collect a couple hundred. So far, she said, nobody has refused to sign and all agree that something needs done. She said she will probably present the petitions to the Yahara Lakes Association, which she hopes will in turn approach the DNR.
But DNR researchers said fluridone may not be the panacea some are hoping it might be.
Jennifer Hauxwell, a DNR research scientist who specializes in lake vegetation, said she has been studying fluridone for the last 1 1/2 years. She has collected data on fluridone’s use on four Wisconsin lakes as well as on lakes in 28 other states around the country.
Although she said more research is necessary, Hauxwell said initial information shows fluridone to be effective only for two to four years to treat Eurasian watermilfoil, the stringy and pesky weeds that choke Madison lakes. But on all the lakes where fluridone was used, Hauxwell said, the weed returned, sometimes worse than before.
On Potter Lake in Walworth County, where the entire lake was treated with fluridone, Hauxwell said watermilfoil remained in check for four seasons but then returned. Hauxwell said the return of the invasive weed may indicate that even though the poison kills the plant itself, seed bedsremain in the lake silt and those beds eventually produce plants again.
Research also hints at other problems with using fluridone for whole lake treatment, Hauxwell added, especially on eutrophic lakes – lakes such as Mendota and Monona that have high levels of nutrients. On such lakes, Hauxwell said, water clarity eventually decreases after the use of fluridone and native plants are killed along with watermilfoil.
Almost no research is available on how the chemical affects fish, Hauxwell said. Some fish biologists, however, believe the chemical has the potential to alter a fish population because it kills native weeds that small forage fish feed on, and the decreasing numbers of those fish will affect populations of larger game fish such as bass and walleye.
“You’re changing things,” said Hauxwell. “And how sustainable this is in the long run, we just don’t know.”
Jeff Bode, the DNR’s section chief for lakes, said that until the science is more complete, fluridone will probably remain a chemical used for spot treatments in extreme situations rather than whole-lake treatments.
Sue Jones, with the Dane County Lakes and Watershed Commission, said the county manages the lakes under a plan approved in 1992. That plan relies on weed cutting, she said, and on crucial long-term solutions such as controlling runoff into the lakes and limiting the use of nutrients such as phosphorus on farm fields and lawns.
“The use of fluridone has been relatively recent,” Jones said. “And it’s been mostly pushed by the manufacturer. But it’s still experimental.”
Lawson said the weeds have become so bad that it may be time to try something more ambitious and, even, experimental. “I just don’t think this is something that evolved over a long time,” she said of watermilfoil. “It’s an invasive that has taken over.”
Hauxwell said such concern is understandable and shows how much people care for the lakes. “Everybody, including the DNR, is wanting a magic bullet,” Hauxwell said. “This is a tool, but it’s not a silver bullet.”
The State of New York Department of Environment Conservation commissioned a study on the impact of certain herbicides on fish. This study shows that fluridone has a negative impact upon younger Walleye. To read the study, please click below:
ATTACHED IS A SCIENTIFIC REPORT WHICH DESCRIBES HOW FLURIDONE CAN IMPACT OUR FRESH WATER MUSSELS. THESE MUSSELS ARE SO IMPORTANT TO THE CLARITY OF OUR LAKE.
TO VIEW THIS REPORT, CLICK BELOW:
THIS IS FROM THE NEW YORK STATE, DEPARTMENT OF ENVIRONMENTAL CONSERVATION
Frequently Asked Questions about Fluridone
What is fluridone and how does it differ from endothall? Fluridone is a slow-acting systemic herbicide used to control nuisance or invasive submerged aquatic vegetation, including Hydrilla and Eurasian watermilfoil. This herbicide can be applied as either a pellet or a liquid. Fluridone works by moving through the plant’s foliage into the root system and/or by being absorbed by the roots through the sediment on the river bottom. The effectiveness is directly related to the plant’s uptake rate and rate of translocation, or the movement of compounds from foliage and roots to the other tissues of the plant.
Fluridone is a systemic herbicide, while endothall is a contact herbicide. The key difference is that contact herbicides damage only the parts of the plant that come in direct contact with the chemical, while systemic herbicides are absorbed by the plant’s foliage and root system and then moved throughout the rest of the plant’s tissues.
How will fluridone be applied? Fluridone will be applied to the Croton River treatment area in the liquid form (trade name Sonar Genesis) via subsurface injection below the New Croton Dam. DEC aims to maintain an herbicide concentration between 2.0 and 4.0 parts per billion (ppb) for 90-120 days. Flow levels in the river fluctuate naturally depending on rainfall, evaporation, and withdrawals. DEC will cooperate with New York City Department of Environmental Protection (NYCDEP) to maintain optimal flows from the New Croton Reservoir to support this project.
Is fluridone toxic to animals or humans? Federal and state herbicide regulations and stringent application guidelines are designed to minimize exposure to non-target species. No lasting negative impacts to waterfowl or wildlife have been observed as a result of fluridone applied at or below the New York State acceptable residual concentration of 50 ppb (NYSDEC, 1994). Fluridone is not considered a carcinogen and has not been associated with genetic mutation or reproductive or developmental issues in test animals (WSDOH, 2000). Studies have shown that fluridone does not bioconcentrate, or exceed the concentration of fluridone in the water, in fish species.
There are several ways in which humans may come in contact with fluridone during or after the treatment period, including drinking water (should fluridone make its way into the well field), swimming, and consuming fish from the river. No adverse human health impacts are anticipated due to exposure to fluridone under the expected conditions of use. Fluridone should not be used for irrigating greenhouse or nursery plants unless an analysis confirms that concentrations are below 1ppb. Water use will not be restricted for swimming or domestic purposes, including bathing, washing dishes and clothing, etc.
Will the application of fluridone harm native aquatic plants? The sensitivity of non-target plants depends on the dosage of fluridone and the duration of treatment. At the low dosage that will be used for treatment, fluridone will be effective at selectively removing Hydrilla and other invasive plants found in the Croton River, including Eurasian watermilfoil and curly-leaf pondweed.
Although some non-target species may be affected, including native pondweeds and water celery, they are expected to at least partially rebound by the subsequent growing season. It should be noted that the negative impacts to native aquatic vegetation from Hydrilla infestation likely outweigh the temporary impacts of the herbicide treatment.
How long does fluridone persist in the environment after treatment? Several factors influence the half-life (time required for a quantity to be reduced to half of its initial concentration) of fluridone in surface water, including water temperature, turbidity (cloudiness), aquatic plant biomass, etc. The process by which fluridone breaks down in the natural environment is called photolysis, or the separation of molecules due to exposure to sunlight. Therefore, the length of time required for fluridone concentrations to drop below the level of detection also depends on the amount of sunlight reaching the river.
Numerous studies have investigated the half-life of fluridone in surface water, and the results have varied from 2 – 3.5 days in a Canadian pond study (Muir and Grift, 1982) to 50 – 75 days in Snyders Lake in New York (Kishbaugh, 2011).
Is water safe to drink or swim in after fluridone treatment? Water usage restrictions after fluridone application are limited to irrigation uses. A health consultation conducted by the North Carolina Division of Public Health (NCDPH) investigated potential impacts to human health from exposure to fluridone in three scenarios, including drinking water with a detectable fluridone concentration, swimming and incidental ingestion of river water, and consuming fish from the treatment area of the river. It was concluded that even at the maximum allowable application rate of 150 ppb (the concentration in the Croton will not exceed 2.0 – 4.0 ppb), the treatment was unlikely to pose a risk to public health (NCDPH, 2015).
What will be done if fluridone is detected in a drinking water well? Drinking water well tests will be conducted daily during the first week of the treatment period, and on a weekly basis for the duration of the treatment. All results will be posted on the DEC project website within 24 hours of sample collection. If fluridone is detected below 1.0 part per billion (ppb), the sample results will be posted as “normal” and the treatment will continue. If the result exceeds 1.0 ppb but are less than 5 ppb, sampling protocol will change and analysis will occur on a daily basis. If detections exceed 4 ppb, treatment plans will be modified or terminated. This protocol has been developed under the guidance of NYSDOH.
The New York State threshold for acceptable organic compound concentration (including herbicides) in drinking water is 50 ppb. The maximum allowable application rate as approved by the Environmental Protection Agency (EPA) is 150 ppb.
References Kishbaugh, S. 2011. Unpublished data. New York State Department of Environmental Conservation. Albany, NY.
Muir, D., N. Grift, B. Townsend, D. Metner, and W. Lockhart. 1982. Comparison of the uptake and bioconcentration of fluridone and terbutryn by rainbow trout and Chrironomous tentans in sediment and water systems. Archives of Environmental Contamination and Toxicology. 11: 595-602.
North Carolina Division of Public Health. 2015. Public health evaluations for potential exposures to fluridone or endothall used for treatment of Hydrilla verticillata in the Eno River, Orange and Durham Counties, NC. Raleigh, NC.
NYSDEC. 1994. Final generic environmental impact statement: use of the registered aquatic herbicide fluridone (Sonar) and the use of the registered aquatic herbicide glyphosate (Rodeo and Accord) in the state of New York. Albany, NY.
WSDOH. 2000. Fluridone fact sheet. Washington State Department of Health. Olympia, W