16 Chemical Controls 16.1 INTRODUCTION Herbicides are chemical pesticides used for plant management. Herbicides kill plants or severely interrupt their normal growth processes. An herbicide formulation consists of an active ingredient, an inert carrier, and possibly other chemicals such as adjuvants that make the herbicide more effective. “Today’s modern (herbicide) applicator strives to selectively treat exotic species encour- aging native species re-establishment, and to treat other excessive vegetation in more ‘direct use’ areas leaving less-utilized areas of native species as nutrient and habitat buffers in the ecosystem.” This quote by Kannenberg (1997) suggests that the role of herbicides in lake and reservoir man- agement is threefold: (1) eradicate exotic species; (2) change plant community composition; and (3) treat excessive vegetation growth in direct or high-use areas. The decision to use herbicides should be based on the same criteria — efficacy; cost; health, safety, and environmental impacts; regulatory appropriateness; and public acceptability- that are used for other management techniques (Chapter 11). This was not always the case. Because herbicide (and other pesticide) treatments were fast, relatively cheap, and many times very effective, they were used in inappropriate ways regarding health, safety and environmental impacts. This influenced public perception about the acceptability of using pesticides. One of the more striking historical cases of overuse of a toxic but very effective aquatic herbicide was the use of sodium arsenite. Between 1950, when the Wisconsin Department of Natural Resources began keeping records and 1970 when it was no longer used, approximately 798,799 kg of sodium arsenite were added to 167 lakes (Lueschow, 1972). The environmental impacts of these treatments were not monitored. However, the use of sodium arsenite causes long-term prob- lems for further management in some lakes where it was heavily used. The sediments in these lakes are a hazardous waste so other lake management options such as dredging become extremely difficult if not impractical (Dunst, 1982). Herbicides are a useful technique in a lake manager’s “tool box.” The largest obstacle to using them may be public perception. Poor public perception can be overcome with good demonstration projects, reliable monitoring (Chapter 11), education, full disclosure of known environmental impacts, and responsible use by applicators. 16.2 EFFECTIVE CONCENTRATION — DOSE, TIME CONSIDERATIONS, ACTIVE INGREDIENTS, SITE-SPECIFIC FACTORS, AND HERBICIDE FORMULATION Aquatic herbicides were originally developed for terrestrial use, mainly for agriculture. In terrestrial systems an effective concentration of active ingredients (a.i.) is applied directly to the plant or the soil. Exposure time is usually not a consideration unless there is a meteorological event like a rainstorm that washes the herbicide off the plant. Similarly, an effective concentration of herbicide can be applied directly to emergent and floating-leaf aquatic species. For submergent species an effective dose is delivered through water so dilution and dispersion are considerations. The water volume treated, currents, drift and micro-stratification (Chapter 11) effect dilution and dispersion. The success or failure of treating any species is dependent on an effective dose of active ingredient contacting or being taken up by the plant. This is dependent on the concentration/expo- Copyright © 2005 by Taylor & Francis sure time (CET) relationship for controlling the target plant (Getsinger, 1997). An effective con- centration can be achieved using a high dose of herbicide and a short contact time or a low dose of herbicide and a long contact time (Figure 16.1). While a low dose of material is more desirable for cost, safety, health, and environmental reasons, an effective CET relationship and thus efficacy is more difficult to achieve for submersed species because any bulk water movements away from the plant affects the CET relationship. This does not imply that an effective dose is always easily achieved for emergent and floating- leaved species. Accurate application requires that the equipment be well calibrated and that the boat or other application vehicle is moving at a constant speed. This is difficult in heavy vegetation and a boat tends to submerge the plants that it passes over, washing off the herbicide. What it does imply is an effective dose of herbicide is easier to calculate for emergent and floating-leaf species. Application rates are calculated based on the area treated. For submergent species, water depth and velocity also need to be considered. Understanding active ingredient is critical to proper CET calculations. Active ingredient is the concentration of herbicidally active chemical in a formulation. It can vary tremendously between different formulations or different manufactures of the same product. It is expressed as weight to volume (g/L) for liquid formulations and weight to weight (g/kg) for granular formulation, or it may be represented as a percentage. For example in a liquid formulation the active ingredients could be expressed as 300 g/L or 30%. Active ingredient concentration is given on the herbicide label. Site-specific treatment factors affect the choice of herbicide formulation, which affects appli- cation equipment, techniques, and timing. For example, a surface application of a liquid formulation is appropriate in quiescent, isothermal water. These conditions allow an even distribution and mixing of a surface application. In a dense plant stand that creates a temperature-stratified environment, or in areas of great water movement, a granular or pellet formulation, or subsurface injection of a liquid formulation, will more evenly distribute the herbicide. 16.3 TYPES OF CHEMICALS There are only six herbicides: copper (Chapter 10), 2,4-D, diquat, endothall, fluridone, and glyphosate, that are registered and commonly used for lake and reservoir management in the FIGURE 16.1 Examples of concentration/exposure time (CET) relationships using endothall for Myriophyl- lum spicatum (A) and Hydrilla verticillata (B) control. The shaded area represents CETs that give 85–100% M. spicatum control with very limited regrowth up to 4 weeks post-treatment and 85–100% Hydrilla control with very limited or no regrowth up to six weeks post-treatment. The CET relationship is different for each species-herbicide combination. (After Netherland, M.D. et al. 1991. In: J. Aquatic Plant Manage. 29: 61–67. With permission.) Concentration, mg ae/l 5 4 3 2 1 0 726660544842363024 Exposure time, hours (a) (b) 181260 Concentration, mg ae/l 5 4 3 2 1 0 726660544842363024 Exposure time, hours 181260 Copyright © 2005 by Taylor & Francis United States. A seventh herbicide, triclopyr, is used under an experimental use permit. Other herbicides may be approved for use in other countries or approved for aquatic uses that are not appropriate to lake and reservoir management because they have a long use restriction time or they are toxic to fish or other aquatic organisms. These herbicides and other chemicals can be categorized in a number of ways depending on their use, mode of contact, selectivity, and persistence in the environment (Table 16.1). 16.3.1 CONTACT VS. SYSTEMIC Contact herbicides act quickly and are generally lethal to the plant cells they contact. Because of their rapid action and other physiological reasons, they do not move extensively within the plant and they kill tissue only where they contact the plant. For this reason they are generally more effective on annual plants (see Table 12.10 in Chapter 12 for information regarding annual vs. perennial plants). Perennial plants can be defoliated by contact herbicides but they regrow from unaffected parts, especially parts that are protected beneath the sediment. Contact herbicides are more effective than systemic herbicides on old, slow growing, or senescent plants, so they are preferred later in the growing season for controlling aquatic nuisances where, for lack of time or for physiological reason, systemic herbicides are not effective. TABLE 16.1 Aquatic Herbicide Characteristics a Compound Formulation b Contact vs. Systemic b Mode of Action b Half-life in Water (days) b,c Method of Disappearance c,d Complexed copper Various complexing agents with copper- liquid and granular Systemic Plant cell toxicant 3 Precipitation Adsorption 2,4-D Butoxyethel ester — salt Dimethylamine — liquid Isooctyl ester — liquid Systemic Selective plant growth regulator 7–48 Microbial degradation Photolysis Plant metabolism Diquat Liquid Contact Disrupts plant cell membrane integrity 1–7 Adsorption Photolysis Microbial degradation Endothall Liquid and granular Contact Inactivates plant protein synthesis 4–7 Plant metabolism Microbial degradation Fluridone Liquid and granular Systemic Disrupts carotenoid synthesis, causing bleaching of chlorophyll 20–90 Photolysis Microbial degradation Adsorption Glyphosate Liquid Systemic Disrupts synthesis of phenylalanine 14; Used over but not in water Adsorption Microbial degradation Triclopyr e Liquid Systemic Selective plant growth regulator —— a Herbicides registered by U.S. Environmental Protection Agency. e Experimental use permit only. Sources: b After Madsen, J.D. 2000. Advantages and Disadvantages of Aquatic Plant Management. Tech. Rept. ERDC/EL MP-00-01. U.S. Army Corps of Engineers, Vicksburg, MS. c After Langeland, K.A. 1997. In: M.V. Hoyer and D.E. Canfield (Eds.), Aquatic Plant Management in Lakes and Reservoirs, NALMS, Madison, WI and Lehigh, FL. pp. 46–72. d After Wisconsin Dept. Nat. Res., 1988. Environmental Assessment Aquatic Nuisance Control (NR 107) Program. Wisconsin Dept. Nat. Res., Madison, WI. Copyright © 2005 by Taylor & Francis Systemic herbicides are translocated from absorption sites to critical growth points in the plant. They act slowly when compared with contact herbicides, but they are generally more effective for controlling perennial and woody plants. They are also more selective than contact herbicides. Correct application rates are critical. If application rates are too high, systemic herbicides can act like contact herbicides. They stress the plants so much that the herbicides are not translocated to critical plant growth areas (Nichols, 1991). 16.3.2 BROAD-SPECTRUM VS. SELECTIVE HERBICIDES Broad-spectrum herbicides control all or most of the vegetation they contact. Selective herbicides control certain plants but not others. Selectivity is based on the different response of different species to the herbicide. It is a function of both the plant and the herbicide. Selectivity can be affected by the CET relationship of the herbicide. For example, water hyacinth (Eichhornia crassipes) is selectively controlled amongst spatterdock (Nuphar sp.) using the rec- ommended rate of 2,4-D, but spatterdock can be controlled by using higher rates and granular formulations (Langeland, 1997). Systemic herbicides are the most physiologically selective herbicides. However, as stated above, they must be translocated to the site where they are active. Herbicides may be bound on the outside of the plant or bound immediately after they enter the plant so they cannot move to the activity site. For other reasons, not all understood, herbicides are more readily translocated in some plants than in others, which results in selectivity (Langeland, 1997). Some plants have the ability to alter or metabolize a herbicide so it is no longer active, and some herbicides affect very specific biochemical pathways so they only work on plants or groups of plants with those pathways (Langeland, 1997). Selectivity is also affected by the physiology of perennial species during their growth cycle. During early stages of growth, energy reserves are translocated upward in the plant so an herbicide taken up by the roots is most effective. Late in the growth cycle, material is translocated downward to the roots so a foliar herbicide is most effective (Langeland, 1997). 16.3.3 PERSISTENT VS. NON-PERSISTENT Persistent herbicides retain their activity in water for a long time, usually measured in weeks or months. Non-persistent herbicides act only when sprayed directly onto foliage or they lose their phytotoxicity rapidly on contact with soil, particulate matter in the water, or plant cells. Non- persistent herbicides may decay rapidly in water. There is no set time that separates persistent from non-persistent. The half-life of the herbicide in water is a useful measure of persistence (Table 16.1). 16.3.4 TANK MIXES In addition to single uses, herbicides are mixed to increase efficacy. Diquat and copper chelates are a popular tank mix that provides a broad spectrum of control for aquatic plants plus the convenience of working with a liquid formulation. 16.3.5 PLANT GROWTH REGULATORS (PGRS) Growth regulators prevent plants from obtaining normal stature. They keep plants short but func- tional by preventing cell division and elongation. PGR research on aquatic plants has occurred for over 15 years. Unfortunately it has yet to be commercialized so PGRs cannot and have not been used for management purposes. Laboratory and field tests show that Thiadiazuron and Bensulfuron Methyl maintained milfoil (Myriophyllum spicatum), hydrilla (Hydrilla verticillata) and Potamogeton spp. in short stature (Anderson, 1986, 1987; Anderson and Dechoretz, 1988; Lembi and Netherland, 1990; Nelson and Copyright © 2005 by Taylor & Francis Van, 1991). Thiadiazuron inhibited tuber and turion production in hydrilla (Klaine, 1986). Bensulfuron methyl inhibited propagule formation in P. nodosus, P. pectinatus, and hydrilla (Anderson, 1987). Growth regulators are a very interesting technology because they have the potential for utilizing the beneficial aspects of aquatic plants without letting them grow to nuisance proportions. There are still many questions to answer regarding product delivery, mode of uptake, mode of action, differential plant responses, efficacy, health, safety, and environmental impacts that probably will not be answered without commercial interest in the technique. 16.3.6 ADJUVANTS Adjuvants are chemicals added to herbicides to increase their effectiveness. There are activator adjuvants, spray-modifier adjuvants, and utility-modifier adjuvants (Thayer, 1998). They include wetting agents and emulsifiers that allow the herbicide to mix more easily. Spreaders allow herbi- cides to spread evenly over treated surfaces. Stickers, thickeners, invert emulsifiers, and foaming agents increase the adherence of the herbicide to the treated surface and help control herbicide drift. Penetrants enhance absorption of herbicides by decreasing surface tension or by penetrating through waxy coatings. Many herbicide formulations contain a small percentage of adjuvants and all the categories of adjuvants mentioned may not be used in the aquatic situation. Wetting agents and spreader-stickers are probably the most frequently used adjuvants (Binning et al., 1985). 16.4 INCREASING HERBICIDE SELECTIVITY Ideally, herbicides should be used to selectively control undesirable species and to change plant community structure to a more desirable type. Past control efforts usually did not take selectivity into consideration and research continues to make herbicides more selective. Some tools for using herbicides selectively are already present and include efficacy information as well as location- selective, time-selective, and dose-selective applications. Using the differential susceptibility of plants to herbicides is one method of selective control. In a mixed plant community, if the undesirable species are controlled by an herbicide and desirable species are not, there is a basis for selective herbicide control based on herbicide efficacy. An example is using 2,4-D to control Eurasian watermilfoil or coontail (Ceratophyllum demersum) in a mixed pondweed (Potamogeton spp.) community. 2,4-D effectively controls milfoil and coontail but not pondweeds. As a basis for planning selective management, herbicide efficacy is summarized in Table 16.2. Label instructions for specific efficacy information should be consulted before using any herbicide. Applications can be selective by carefully placing the herbicide on target plants and avoiding non-target plants. Experienced personnel for example, using a handgun applicator, can control small areas of water hyacinth among bulrushes (Scirpus sp.) using 2,4-D and careful placement of the herbicide on the target plant (Langeland, 1997). Likewise, if diquat were used in the above scenario, although it is a broad-spectrum, contact herbicide, it would only kill bulrush stems above the waterline. The extensive underground bulrush roots and rhizomes are not affected and the plant regrows after the initial effect of the herbicide (Langeland, 1997). Adjuvants that restrict herbicide movement are a way of selectively treating an area. This method is especially appropriate for treating areas that are monotypes of nuisance species while keeping the herbicide from drifting into a valuable plant community. Another method of restricting herbicide movement is to treat in conjunction with a drawdown. The sediments of Lake Ocklawaha, Florida were treated experimentally with fluridone and other chemicals under drawdown conditions to test the efficacy of controlling hydrilla plants and tubers (Westerdahl et al., 1988). Herbicides can be precisely placed in terrestrial areas. Water temperature and light influence macrophyte growth, physiological status, and phenology. Most herbicides work best when plants are actively growing. Some species, Elodea canadensis, P. Copyright © 2005 by Taylor & Francis TABLE 16.2 Aquatic Plant Response to Herbicides Commonly Used for Lake and Reservoir Management a Glyphosate 2,4-D Endothall Diquat Fluridone Emergent and Floating-Leaf Species Acorus calamus —C——— Alternanthera philoxeroides CC CC — — CC Brasenia schreberi — C CC CC CC Eleocharis spp. — — — — CC Glyceria borealis ———C— Hydrocotyle umbellate —CC—C — Justicia americana —C—CCCC Ludwigia uruguayensis — C CC CC CC Lythrum salicaria C———— Nasturtium sp. — C — — — Nelumbo lutea CC C CC — — Nuphar spp. CCCC—CC Nymphaea odorata CCCC—CC Phragmites spp. CC — — — — Polygonum spp. CC CC CC CC CC Pontederia sp. CC CC — — — Salix spp. C C — — — Sagittaria spp. C C — — C Scirpus spp. C C — CC C Sparganium spp. — — C — — Trapa natans —CC——— Typha spp. C CC — CC CC Floating Species Azolla caroliniana — CC — CC CC Eichhornia crassipes CC C CC C — Lemna spp. — CC CC C C Pistia stratiotes CC CC CC C — Salvinia rotundifolia ——CCCCC Spirodela polyrhiza —CC—CCC Wolffia columbiana ———CCCC Wolffiella floridana ———CCCC Submergent Species Cabomba caroliniana — CC C CC CC Ceratophyllum demersum —CCC CCC Chara spp. b ————— Egeria densa ——CCCCC Elodea canadensis ——CCCC Hydrilla verticillata b — — CC CC CC Myriophyllum aquaticum —CCC— Myriophyllum spicatum —CCCCC Najas spp. — CC C C CC Potamogeton spp. — — C CC CC P. richardsonii ——C—C Ranunculus aquatilis ——CCC— Ruppia maritima ——CCC— Utricularia spp. — CC — CC CC Copyright © 2005 by Taylor & Francis crispus, and M. spicatum for example, grow better at low water temperatures and appear earlier in the growing season than many other species. This provides an opportunity to treat these species with a contact or short-lived systemic herbicide before other species are actively growing. Refer to Chapter 11 for a discussion of the importance of phenology and resource allocation patterns when determining management strategies. A thorough knowledge of CET relationships allows selective management based on varying dose or contact time of the same herbicide. The water hyacinth and spatterdock example was given above. An endothall label suggests that P. crispus can be effectively treated at about one-half the concentration needed to control P. americanus and many emergent and free-floating species. Adams and Schulz (1987) found that M. spicatum and E. canadensis were highly sensitive to low concen- trations of diquat. “Fine tuning” treatments based on CET relationships constitute a very active area of research. It is not easy because of previously mentioned problems of dispersion and dilution but it is an area that holds great promise for selectively managing plant communities with herbicides and for reducing environmental impacts from herbicide treatments. 16.5 ENVIRONMENTAL IMPACTS, SAFETY AND HEALTH CONSIDERATIONS 16.5.1 H ERBICIDE FATE IN THE ENVIRONMENT Knowing the fate of aquatic herbicides in the environment is important for determining environ- mental impacts, safety and health. How long do herbicides persist in the environment, what are the breakdown products, where do the herbicides or breakdown products go when they “disappear” are all important questions. Disappearance refers to the removal of the herbicide from a certain part of the environment (Langeland, 1997). Aquatic herbicides disappear by dilution, adsorption Vallisneria americana — — CC CC — Zannichellia palustris ——C—— Zosterella dubia —CC—— Note: C, controlled by the herbicide; CC, conditionally controlled by the herbicide; this could mean that efficacy depends on specific formulation or application techniques, that it was rated as only fair or good control by Westerdahl and Getsinger (1988), or that it is labeled only for partial control. —, not controlled by the herbicide, not registered for use with this species, or information is unknown. a For use as a general guide; read label instructions for details. b Can be controlled by copper or copper complexes. Source: After Lembi, C.A. and M. Netherland. 1988. Category 5, Aquatic Pest Control. Dept Botany, Purdue University, W. Lafayette, IN; Westerdahl, H.E. and K.D. Getsinger. 1988. Aquatic Plant Identification and Herbicide Use Guide, Volume II: Aquatic Plants and Suscep- tibility to Herbicides. Aquatic Plant Cont. Res. Prog. Tech. Rept. A-88-9. U.S. Army Corps of Engineers, Vicksburg, MS; Binning, L., B. Ehart, V. Hacker, R.C. Dunst, W. Gojmerac, R. Flashinski and K. Schmidt. 1985. Pest Management Principles for Commercial Applicator: Aquatic Pest Control. University Wisconsin-Ext., Madison; Cooke, G.D. 1988. In: The Lake and Reservoir Guidance Manual. USEPA 1440/5-88-02. pp. 6-20–6-34. TABLE 16.2 (Continued) Aquatic Plant Response to Herbicides Commonly Used for Lake and Reservoir Management a Glyphosate 2,4-D Endothall Diquat Fluridone Copyright © 2005 by Taylor & Francis to bottom sediments, volatilization, absorption by plants and animals, and by dissipation. Herbicides dissipate by photolysis, microbial degradation, or metabolism by plants and animals. The rate of disappearance (Table 16.1, half-life) depends upon: (1) initial herbicide concentration, (2) water movement, (3) temperature, (4) amount of plant matter, (5) water chemistry, (6) water volume, (7) the presence of decomposing organisms, and (8) the mode of disappearance. Table 16.1 summarizes the methods of herbicide disappearance. Of the contact herbicides, endothall biodegrades into carbon dioxide and water. Diquat is rapidly taken up by plants or binds tightly to particles in the water or bottom sediments. When bound to clay mineral particles, diquat is not biologically available. When bound to organic matter, microorganisms slowly degrade diquat. It is photo-degraded to some extent when applied to leaf surfaces. Information about the persistence or biological effects of degradation products of diquat was not found (WDNR, 1988). Microbial action is the primary mode of degradation of 2,4-D and photolysis may be important under alkaline conditions (WDNR, 1988). 2,4-D degrades into naturally occurring compounds. 2,4- D amine for example degrades to carbon dioxide, water, ammonia, and chlorine (Langeland, 1997). Dissipation of fluridone from water occurs mainly by photo-degradation. Microbial breakdown is probably the most important method of breakdown in bottom sediments. Degradation rate is variable and may be related to the time of year of application. Applications when days are shorter and sun’s rays less direct result in longer half-lives. Fluridone usually disappears from water after 3 to 9 months. It usually remains in bottom sediments between 4 months and 1 year (Langeland, 1997). Although glyphosate is not applied directly to water, when it does enter water, binding to particulate matter and to bottom sediments inactivates it. It is degraded to carbon dioxide, water, nitrogen, and phosphorus over a period of several months (Langeland, 1997). Complexing is the major means of removing soluble copper ions from water. The copper ion is chemically bound by carbonate and hydroxide ions in natural waters as well as by organic humic acids. This binding is rapid in high alkalinity, hardness, and pH waters. Some lakes received massive doses of copper over an extended period of time. Lakes Kegonsa and Waubesa in Dane County, Wisconsin were treated with 586,750 kg and 692,182 kg, respectively, of copper sulfate between 1950 and 1970 (Lueschow, 1972). Copper sulfate was applied to the five Fairmont Lakes in southern Minnesota at cumulative rates of 1647 kg/ha over a 58-year period (Hanson and Stefan, 1984). Copper concentrations in lake sediments of the Dane County lakes were as high as nearly 1% of total sediment weight (WDNR, 1988). In the Dane County lakes the highest concentration of copper is found in sediments at the greatest water depth and copper concentration decreases toward the top of the sediment, which indicates the sediments with the highest copper concentration are being buried. There appears to be an annual copper cycle in the lakes with greater copper concentrations found in the water during the autumn lake turnover. Increased copper levels are largely in the suspended organic fraction of the water; relatively small increases have been observed in soluble copper (WDNR, 1988). See Chapter 10 for additional details about copper. The active ingredients are not the only chemicals added to the waters. Inert ingredients, manufacturing contaminants, and adjuvants are also added. The fates of some of these products have been studied but generally their fate is less well known than the fate of the active ingredients. Modeling is becoming an increasingly important tool for characterizing ecological risks of using pesticides in aquatic environments at the individual, population and community levels (Bartell et al., 2000). 16.5.2 TOXIC EFFECTS In the United States, the United States Environmental Protection Agency (USEPA) registers aquatic herbicides for use. An herbicide can be registered if it does not cause “unreasonable adverse effects” to human health or the environment. Registration does not mean that an herbicide has no health or environmental risks. Herbicide registration decisions balance the risks involved with the benefits. Copyright © 2005 by Taylor & Francis The USEPA decides whether or not to register an herbicide after considering the ingredients; the manufacturing process; the physical and chemical properties; the mobility, volatility, breakdown rates, and accumulation potential in plants and animals; the toxicity to animals; and the carcinogenic or mutagenic properties. The USEPA can approve or disapprove registration of a new herbicide and may further restrict or cancel the registration of those in use. An herbicide’s capacity to harm fish, plants, and other aquatic life depends on the toxicity of the herbicide, the dose rate used, the exposure time of the affected organism, and the persistence of the herbicide in the environment. Toxic effects may be direct or indirect. Direct effects impact the organism of concern. Direct effects may be lethal if they kill the organism or they can be sub- lethal. Sub-lethal or chronic effects include biomass loss, low resistance to disease, compromised reproduction rates or sterility, loss of attention, low predator avoidance, and deformed body parts. The short-term indirect effects are the ecological effects caused by the death and decay of the target plants. Long-term effects are changes caused by a restructuring of the plant community or broader ecological changes like the change in stable-state from a macrophyte-dominated lake to an algae- dominated lake, or changes in food webs (Chapter 9). The direct and indirect impacts of herbicide use are summarized in Figure 16.2. 16.5.2.1 Direct Effects The most obvious direct toxic effect is damage to non-target aquatic plants. This can occur to plants present in the targeted treatment area or it can affect plants not in the target area by spray drift or residue movement in water currents. The potential for this impact can be calculated knowing the CET relationship between the non-target species, the herbicide, and the herbicide concentration after considering dissipating factors. The lethal and sub-lethal effects to invertebrates, fish, and higher animals or humans are not as easily assessed. A variety of tests and extrapolations are performed on aquatic organisms to ascertain herbicide toxicity. Acute toxicity is usually reported as lethal concentration, effective concentration, or tolerance limit (WDNR, 1988). A lethal concentration (LC) is the concentration that kills 50% of the test organisms in a given time period such as 24, 48, or 96 hours. It is one of the most commonly tested and reported parameters for fish and other aquatic organisms. It is reported as LC 50, 24, 48, or 96 hours. The effective concentration is the dosage that immobilizes the test organism. It is often used for insects and crustaceans where determining death is difficult. The tolerance limit is an extrapolated or mathematically determined concentration used to estimate the point of toxicity. The “no observable effect” level is another means of reporting toxicity. It is the highest test concentration that shows no observable impact on the test organisms. Most assays are conducted under laboratory conditions that allow careful control over a wide variety of factors affecting test results. Such simplified tests present obvious difficulties interpreting the impacts of an herbicide on a complicated, dynamic system like a lake. There is also a concern over the species and life stages selected for testing (Paul et al., 1994). It is impossible to test all potentially affected organisms, at all life stages, in all habitat conditions. Many of the test species may not occur in the area where the herbicide is used. The bulk of the published data on herbicide toxicity to aquatic biota relates to effects on invertebrates and fish but there are effects on phytoplankton, micro-organisms, and higher animals. Many higher animals are not obligate aquatic organisms so less attention has been paid to them. However, some higher animals like frogs and toads are obligate aquatic organisms in early life stages. Sub-lethal or chronic effects are probably even more difficult to assess than lethal effects. How do you tell if a bluegill is not feeling well today? The main ways are through population, growth, and life-cycle studies that can be extremely complex in a lake or reservoir ecosystem. The objective of this section is not to review all the toxicological data and do a risk assessment for aquatic herbicides, but to give some idea of the complexity of the task. The information is too voluminous and should be done by a professional toxicologist. To learn more, the best resources Copyright © 2005 by Taylor & Francis FIGURE 16.2 Possible effects of a herbicide application on the aquatic ecosystem. Main effects are indicated by thick lines. (From Murphy, K.J. and. P.R.F. Barrett. 1990. In: A. Pieterse and K. Murphy (Eds.), Aquatic Weeds, The Ecology and Management of Nuisance Aquatic Vegetation. Oxford University Press, Oxford, UK. pp. 136–173. With permission of the original author, David Mitchell.) Loss of habitat and food for animals Decrease of certain non-susceptible animals Photosynthesis in system decreased Increased light penetration pH levels decrease Increase in non-susceptible plants Photosynthesis in system increased Increase of certain non-susceptible animals pH levels increased Increase in bacteria, fungi and detritivores Autolysis and decomposition of dead material Increase of CO 2 Decrease in CO 2 Decrease of O 2 Increase in O 2 Weeds killed Other susceptible plants killed Herbicide applied Susceptible animals killed Release of plant nutrients Anaerobic conditions Production of CH 4 and H 2 S Aerobes killed Increase in anaerobes Copyright © 2005 by Taylor & Francis [...]... non-treated lakes In all cases, post treatment plant cover was maintained at levels above 60% Eurasian watermilfoil was not eliminated in any of the lakes (Tables 16. 10 16. 13) Only time will tell whether it returns to its former dominance Curly-leaf pondweed also became more dominant, at least over the short-term, in Big Crooked and Lobdell Lakes (Tables 16. 10 and 16. 11) However, Najas guadalupensis and. .. Rept ERDC/EL TR-0 2-3 9 U.S Army Corps of Engineers, Vicksburg, MS 16. 7.1.4 Vermont Experiences — Lake Hortonia and Burr Pond Lake Hortonia and Burr Pond (Table 16. 3) were treated with low doses of fluridone to determine whether submersed plant diversity and frequency were impacted in the year of treatment and beyond when targeting Eurasian water-millfoil control Both lakes had widespread and diverse aquatic... Flashinski and K Schmidt 1985 Pest Management Principles for Commercial Applicator: Aquatic Pest Control University of WisconsinExt., Madison Brooker, M.P and R.W Edwards 1973 Effects of the herbicide paraquat on the ecology of a reservoir Freshwater Biol 3: 157–176 Cooke, G.D 1988 Lake and reservoir restoration and management techniques, In L Moore and K Thorton (Eds.), The Lake and Reservoir Restoration. .. Tech Rept A-9 8-1 U.S Army Corps of Engineers, Vicksburg, MS Scheffer, M 1998 Ecology of Shallow Lakes Chapman Hall, London Scheffer, M., S.H Hosper, M.-L Meijer, B Moss and E Jeppesen 1993 Alternative equilibria in shallow lakes Trends Ecol Evol 8: 275–279 Shearer, R.W and M.T Halter 1980 Literature Reviews of Four Selected Herbicides: 2,4-D, Dichlobenil, Diquat, and Endothall Municipality of Metropolitan... technology On-board computers, fathometers, global positioning (GPS) units, and digital flow meters allow applicators to be much more precise with the area treated and treatment doses (Figure 16. 4) (Kannenberg, 1997) Low-dose applications of fluridone and endothall and new formulations of 2,4-D and copper chelates are products or techniques that reduce environmental risk (Kannenberg, 1997) FIGURE 16. 4 Typical... Koschnick, M.D Netherland, R.M Stewart, D.R Honnell, A.G Staddon and C.S Owens 2001 Whole-Lake Applications of Sonar for Selective Control of Eurasian Watermilfoil Rep ERD/EL TR-0 1-0 7 U.S Army Corps of Engineers, Vicksburg, MS Getsinger, K.D., J.D Madsen, T.J Koschnick and M.D Netherland 2002a Whole lake fluridone treatments for selective control of Eurasian watermilfoil: I application strategy and herbicide... weeds, In A Pieterse and K Murphy (Eds.), Aquatic Weeds, The Ecology and Management of Nuisance Aquatic Vegetation Oxford University Press, Oxford, UK pp 136–173 Nelson, L.S and T.K Van 1991 Growth Regulation of Eurasian Watermilfoil and Hydrilla using Bensulfuron Methyl Aquatic Plant Cont Res Prog Rep A-9 1-1 U.S Army Corps of Engineers, Vicksburg, MS Netherland, M.D., W.R Green and K.D Getsinger 1991... Parkers, Zumbra, and Crooked Lakes were selected for this evaluation (Table 16. 3) All were spring treatments, and targeted whole lake fluridone concentrations were 10 μg/L for Parkers and Zumbra Lakes and 15 μg/L for Crooked Lake Fluridone treatment reduced the percentage of sampling stations with vegetation in both Parkers and Zumbra Lakes (Table 16. 4) In Lake Zumbra the average number of vascular plants... most of the regrowth was from stem fragments carried into the treated areas from adjacent, non-treated areas The relative frequency of milfoil dropped from pretreatment levels of 50% (river plot) and 42% (cove plot) to 16. 5% and 9.7% 1 year after treatment and 25.1% and 20.2% 2 years after treatment (Table 16. 18) indicating the drop in milfoil importance in the plant community In contrast, coontail and. .. factor of 4, and reduced depression of dissolved oxygen occurred beneath vegetation mats (Langeland, 1998) By using maintenance management on the St John River, Florida, the U.S Army Corps of Engineers reduced the area of Pistia stratiotes that needed treatment from 881 ha to 33 ha and the area of water hyacinth that needed treatment from 649 to 28 ha between 1995 and 2000 (Allen, 2001) Maintenance management . than 40 ha), and (3) is located in an area with no other milfoil lakes (Welling et al., 1997). 16. 7.1.2 Wisconsin Experiences — Potters and Random Lakes Potters and Random Lakes (Table 16. 3) in southeastern. Advantages and Disadvantages of Aquatic Plant Management. Tech. Rept. ERDC/EL MP-0 0-0 1. U.S. Army Corps of Engineers, Vicksburg, MS. c After Langeland, K.A. 1997. In: M.V. Hoyer and D.E. Canfield (Eds.),. Guidance Manual. USEPA 1440/ 5-8 8-0 2. pp. 6-2 0– 6-3 4. TABLE 16. 2 (Continued) Aquatic Plant Response to Herbicides Commonly Used for Lake and Reservoir Management a Glyphosate 2,4-D Endothall Diquat Fluridone Copyright