Aquatic Weed Control in Ponds - Aquaculture at Kentucky State ...

Aquatic Weed Control in PondsRobert M. Durborow, Craig S. Tucker, Boris I. Gomelsky,Richard J. Onders, and Steven D. Mims

Robert M. Durborow, Ph.D., ProfessorState Extension Specialist for AquacultureAquaculture Center, Kentucky State UniversityFrankfort, Kentucky 40601Telephone: (502) 597-6581Fax: (502) 597-8118Email: robert.durborow@kysu.eduCraig S. Tucker, Ph.D., ProfessorDirector of Southern Regional Aquaculture CenterDelta Research and Extension CenterMississippi State UniversityStoneville, Mississippi 36842Boris I. Gomelsky, Ph.D., Associate ProfessorAquaculture CenterKentucky State UniversityFrankfort, KY 40601Richard J. Onders, Research Co-investigatorAquaculture CenterKentucky State UniversityFrankfort, KY 40601Steven D. Mims, Ph.D., ProfessorAquaculture CenterKentucky State UniversityFrankfort, KY 406012

Aquatic Weed Control in PondsBob Durborow, Craig Tucker, BorisGomelsky, Rick Onders and Steve MimsPonds are ideal habitats foraquatic plants, and some will always bepresent. Plants are a necessarycomponent of pond ecosystems becausethey perform valuable functions.Photosynthesizing plants produceoxygen that is needed to sustain fish life.Also, plants assimilate ammonia that isexcreted by fish thereby helping toprevent accumulation of potentially toxicconcentrations of ammonia.Nevertheless, plants can cause problemsin ponds and control measures oftenmust be used to eliminate or reduce theirabundance.Types of weedsThe plants that grow in pondscan be categorized into two groups. Thealgae are primitive plants that have notrue roots, stems, or leaves, and do notproduce flowers or seeds. Algae can becategorized as phytoplankton orfilamentous algae.The higher aquatic plants aremore advanced, and usually have roots,stems, and leaves, and produce flowersand seeds. Higher aquatic plants caneither be submersed, emergent, orfloating.AlgaePhytoplankton. These algae aremicroscopic simple plants suspended inwater or forming floating scums of nearmicroscopiccolonies on pond surfaces.Communities of phytoplankton arecalled the “bloom.” There are hundredsof species of phytoplankton, andidentification of the different species isdifficult, requiring a microscope.Phytoplankton are the mostcommon type of plant found in ponds.Moderate densities of phytoplankton aredesirable in ponds because they shadethe pond bottom preventingestablishment of more troublesome typesof plants. Phytoplankton become a weedproblem when they become excessivelyabundant or when certain undesirablespecies become dominant in thecommunity. Excessive phytoplanktonabundance causes serious water qualityproblems such as frequent periods ofdangerously low concentrations ofdissolved oxygen. This problem is oftenassociated with dense blooms of bluegreenalgae (Figures 1 & 2). The bluegreenbloom floats to the top of the pondforming a scum that can block sunlightand prevent proper photosynthesis.These blooms can also cause an offflavorproblem in fish raised inaquaculture ponds.Figure 1. Blue-green algae(cyanobacteria) forming a surface scum.Figure 2. Blue-green algae floating on apond surface.3

Filamentous algae. Mostfilamentous algae begin growing on thebottom of the pond and rise to thesurface when gas bubbles becomeentrapped in the plant mass. They formmats of cottony or slimy plant material.These filamentous algae are also knownas “pond scum” or more commonly“moss.” However, one type offilamentous algae, Chara spp.,resembles submersed higher plants ingrowth habit. It is weakly anchored inthe mud and grows up through the water.Positive identification of the differenttypes of filamentous algae usuallyrequires a microscope. Control methodsare similar for all filamentous algaeexcept Pithophora spp., which is veryresistant to most copper-based algicidesand requires special treatment. It is thusimportant to identify the species offilamentous algae present in the pond toensure the proper treatment is selected.The most common filamentous algae inponds are:Hydrodictyon spp. (waternet) – each cellis attached repeatedly to two othersforming a repeating network of 5 or 6-sided mesh that looks like a “fish net”stocking (Figure 3).Figure 3. Microscopic view of water net(Hydrodictyon sp.). Photo from theInternet.Spirogyra spp. – usually a dark greenslimy mass that can be pulled apart anddrawn out into fine filaments (Figure 4).This algae usually is easy to identifymicroscopically because the chloroplastis spiraled in a characteristic“corkscrew” along the inside of the cellwall (Figure 5).Figure 4. The filamentous algae,Spirogyra sp. is slick and slimy andpersists in ponds throughout the winter.It often goes away in hot summertemperatures.Figure 5. Spiraled chloroplast inmicroscopic photograph of Spirogyra sp.Pithophora spp. – probably the mostnoxious and difficult filamentous algaeto control. Pithophora spp. is irregularlybranched, not slimy, and somewhatcoarser than masses of Spirogyra spp. Amass of Pithophora spp. feels like wetwool to the touch (Figure 6). Thedistinguishing microscopic characteristicis the presence of barrel-shaped sporesalong the filament (Figure 7).4

Figure 6. The filamentous algae,Pithophora sp. is more coarse (like wetwool) compared to Spirogyra sp. It isvery difficult to control chemically.Figure 7. Microscopic photograph of theterminal of a filament of Pithophora sp.showing the dark, swollen spores thatare characteristic of the genus.Chara spp. – a more advanced group ofalgae which resembles submersed higherplants in growth habit. This plant iscommonly called “muskgrass” becauseof the garlic or skunk-like odor releasedwhen it is crushed. Masses of Chara spp.are serrated and feel rough or crustywhen crushed in the hand (Figure 8).Figure 8. Muskgrass (Chara sp.) Photofrom University of Arizona.Filamentous algae areaesthetically undesirable, giving thepond a “clogged-up” overgrownappearance, and they interfere withfishing by snagging the fisherman’shook. In aquaculture, filamentous algaecan prevent fish or shrimp from beingharvested by seine nets. Seines may rideup over the mass of weeds, allowing fishto escape, and the weight of plantmaterial caught in the seine may strainequipment or completely stop theharvesting process. Even if seining ispossible, fish or shrimp may becomeentangled in the mass of weeds in theseine and will be stressed as workerspick through the weeds to recover them.This is particularly a problem withfingerlings and shrimp.Higher aquatic plantsSubmersed plants. Submersedplants spend their entire lifetime beneaththe surface of the water, although theflower may extend above the surface.Usually the plants are rooted in the mud,but masses of plants may tear loose andfloat free in the water. These plants areobjectionable because they interfere withfishing and fish harvest. The mostcommon submersed higher aquaticplants in ponds are:Najas guadalupensis (bushy pondweed)– rooted, submersed plants with slenderbranching stems and narrow ribbon-likeleaves arranged opposite or in whorls ofthree. Bushy pondweed is a commonsubmersed weed problem in ponds(Figure 9).5

Figure 9. Bushy pondweed (Najas sp.) isa submersed aquatic plant.Potamogeton pectinatus (sagopondweed) – rooted, wholly submersedplants with long, narrow leaves taperingto a point. The stems are irregularly (andoften highly) branched (Figure 10).Figure 10. Sago pondweed(Potamogeton pectinatus) is a submersedplant with long ribbony leaves.Ceratophyllum demersum (coontail) –these plants have long thin stems whichare not rooted. The leaves are in whorlsand are forked (Figure 11).Figure 11. Coontail (Ceratophyllumdemersum) is a submersed aquatic plant.Photo from U. of Florida on the Internet.Emergent plants. Emergentaquatic plants are rooted in the bottommud and grow above the water. Manycan also grow under strictly terrestrialconditions. The plants are rigid and notdependent on the water for support.Emergent plants usually infest only thepond margins and other shallow areasresulting from inadequate pondconstruction, water-shortage conditions,or excessive bank erosion. If stands ofemergent plants become too dense orwidespread, they may interfere withfishing, seining or feeding of fish. Theycan also create a habitat that harborssnakes. Fast-growing emergent plantssuch as smartweed (Polygonumpennsylvanicum) inhabit shallow areasquickly and can often outpace the risingwater level when ponds fill slowly (e.g.during dry seasons or if only a slowflowingwell is available to fill thepond).The most common emergentweeds in ponds are:6

Polygonum spp. (smartweed) – leavesare alternate and elliptical on this plant.The stem is erect and jointed, with eachswollen node covered by a thin sheath.Flowers are usually white or pink(Figure 12).Figure 14. Willows (Salix sp.) grow onthe pond’s edge and get in the way ofseining and other pond operations.Figure 12. Smartweed (Polygonum sp.)inhabits shallow areas of ponds.Typha spp. (cattails) – cattails arefamiliar plants with stout, erect stems upto 8 feet tall. Leaves are stout, long, flatand ribbon-like. The flowers are brownand cigar-shaped (Figure 13).Floating plants. This categoryincludes free-floating plants such asduckweeds (Figure 15) and watermeal(Figure 16), and floating-leaf plants,such as water lilies. Many floating plantsare present only when pond waters arerelatively stagnant and sheltered fromwinds. Small recreational ponds oftenhave problems with duckweed (Lemnaspp.) and watermeal (Wolffia spp.). Inaquaculture ponds, on the other hand,periodic draining and refilling, andfrequent fish harvest activity makeconditions unfavorable for these plants;these larger ponds are often unshelteredfrom the wind, and duckweeds arecontinually washed ashore where theydry up and die.Figure 13. Cattails (Typha sp.) growalong a pond’s edge in shallow water.Salix spp. (willows) – shrubs or treeswith simple, elliptical leaves in alternatearrangement (Figure 14).Figure 15. Duckweed (Lemna sp.) hassmall leaves and roots.7

Figure 16. Watermeal (Wolffia sp.) feelsgrainy like corn meal. Photo from TexasA&M University on the Internet.Occurrence of weed problemsSome plant life will always bepresent in ponds, but the type of aquaticplant community that becomesestablished in a pond depends on therelative abilities of particular plants tocompete for resources. The growth ofphytoplankton is favored in waters withhigh concentrations of nitrogen,phosphorus, and other plant nutrientsdissolved in the water. Phytoplanktonare efficient at using dissolved nutrientsand reproduce rapidly. Once established,the phytoplankton community competeseffectively for nutrients and also restrictsthe penetration of light so that plants thatgerminate on the bottom do not receiveenough light to continue growing.Rooted submersed plants tend toestablish in ponds with low supplies ofnutrients in the water. These ponds oftenare clear with light penetrating to thebottom, and rooted plants can use thenutrients in the bottom mud for growth.Established stands of submersed weedscompete for nutrients and light andprevent phytoplankton from becomingestablished. Some submersed plants alsoproduce chemicals that inhibit thegrowth of phytoplankton.Emergent plants usually colonizeonly the margins of ponds where thewater is less than 2 to 3 feet deep. Iflevees or banks of the pond are erodedand have large areas of shallow water,expansive growths of emergent plantsmay be present. Emergent plants arerooted and can use nutrients in the mud.Thus, their establishment is also favoredby low nutrient levels in the water.Aquaculture ponds containingfood-sized fish receive high levels ofnutrients from daily feeding offormulated fish food. These ponds,therefore, rarely have submersed oremergent aquatic weed problems; thenutrients in the water promote anactively growing phytoplankton bloomwhich, in turn, shades the pond bottomand prevents weed growth. Aquaculturefingerling production ponds, on theother hand, receive fairly low levels ofnutrients because of the smaller biomassof fish; these ponds are much morelikely to have a scant phytoplanktonbloom and a problem with macrophyticplant growth such as submersed andemergent weeds. Likewise, recreationalponds, especially ones that are notfertilized, also have a tendency to havean inadequate bloom and a macrophyticweed problem such as Najas spp. (bushypondweed).Environmentally-sound and costeffectiveaquatic weed managementdepends on the type of plant, the extentof plant coverage, the species and lifestageof fish or crustaceans in the pond,water quality, time of year, and weather.Understanding these interactions, whichdiffer for each weed problem, is largelya matter of experience. Until thatexperience is gained, seek advice fromprivate consultants or experts atuniversities.8

Prevention of aquatic weedsAlmost any plant can be toleratedas long as it does not become soabundant that it interferes with theintended use of the pond. It is, however,difficult to predict whether a smallinfestation of weeds will spread andbecome a problem, so most controlmeasures are implemented when fairlylarge stands of weeds have alreadybecome established. At that time, usingherbicides is usually the fastest way toeradicate weeds and re-establish aphytoplankton bloom, which is usuallythe most desirable plant form in ponds.Chemical weed control is, however,risky in fish ponds because water qualitydeteriorates when dense stands of weedsare killed. Prevention of weeds is apreferred approach to aquatic plantmanagement.Certain management procedurescan be used to minimize the chances ofinfestations of submersed and emergentplants and filamentous algae. Suchprocedures should become part ofcommon pond management and mayhelp avoid the use of chemical controlmeasures.Pond construction. Mostnoxious weed growth starts in theshallow (less than 2 ½ feet deep) areasof ponds. If the area of the pond wherelight can penetrate to the bottom isreduced, rooted plants have less chanceto become established. Pond leveesand/or dams should have a fairly abruptslope of about 3:1 (3 feet out toward thecenter of the pond for every 1 foot droptoward the pond bottom) or 4:1. A slopeof greater that 4:1 would be too gradualand would create excessive shallow area,while a slope of less than 3:1 would betoo steep making the levee prone toerosion and sloughing-off. Plans shouldbe made during construction for theshallowest part of the pond to be noshallower than 2 ½ feet when the pond isclose to full (near the top of the drainpipe).Refilling an empty pond. Inmany cases a newly constructed pondwill be completed by the end of summer(by the time the dry period of the yearends). The rainiest part of the yeartypically will occur during fall andwinter, and the new pond will fill fromrain run-off from the watershed during atime when weeds are less likely to grow.Ponds with a well water source areideally filled during winter for this samereason. If they are filled during othertimes, it is best to fill the pond as quicklyas possible from the well to attain anadequate water depth that will preventaquatic weed growth. (If one well servesfour ponds, for example, one pondshould be filled at a time to minimize thetime needed to get the proper depth forweed control). Also, grass carp may bestocked to prevent growth of nuisanceweeds. About seven triploid grass carpper acre is a good preventive stockingrate. In addition, ponds can be left emptyuntil the farmer plans to actually stockand begin feeding his fish unless thepond is made of highly structured clay(stereotypically red clay); in this case,allowing the pond to dry out wouldpromote deep cracking of the pond’sclay lining which could cause leakswhen the farmer attempts to refill thepond at a later date. If water needs to bemaintained in a pond, a fertilizationprogram can help to prevent the waterfrom being clear. Fertilization promotesa healthy phytoplankton bloom that willshade out sunlight from reachingpotential weeds attempting to germinateat the bottom of the pond.Fertilization. Theimplementation and continued use of the9

proper fertilization program is perhapsthe best method of preventing the growthof troublesome weeds in recreationponds as well as fry nursery ponds. Toavoid weed problems, establish aphytoplankton bloom as quickly aspossible after filling the ponds. The bestway to do this is to add inorganicfertilizers to the pond. The keyingredient in fish pond fertilizers isphosphorus. The most commonphosphorus source in bagged, granularfertilizers is triple superphosphate (0-46-0). It should be noted, however, thatwhen triple superphosphate is broadcastover ponds, it settles to the bottombecause the granules are very insoluble.Most of the phosphorus reacts with thebottom mud and never reaches the water.Any phosphorus that dissolves while thegranules settle through the water quicklyreacts with calcium in the water and ischanged into unavailable calciumphosphate. Granular fertilizers shouldbe put on an underwater platform or in aporous container so they can dissolveslowly into the water before they contactthe mud bottom.Liquid fertilizers are moreeffective than granular fertilizers atstimulating a phytoplankton bloom,especially in hard, alkaline waters. Thephosphorus in liquid fertilizers is alreadyin solution and immediately available foruptake by the phytoplankton. Althoughthe phosphorus from liquid fertilizersalso will eventually become unavailabledue to reactions with calcium in thepond water, it remains in solution longenough to be taken up in adequatequantities by the phytoplankton.The most common, and best,analysis for liquid fertilizers runs fromabout 10-34-0 to 13-38-0. This generalanalysis of about three times as muchphosphorus (expressed as P 2 O 5 ) asnitrogen (expressed as N) has beenfound to have an excellent balance. Therate used successfully by manycommercial fish producers is about 1quart per acre applied every other dayfor 3 to 14 days or until a noticeablephytoplankton bloom develops. Liquidfertilizer is heavier than water, so itshould first be diluted in water before itis applied to the pond, preventing it fromsinking into the bottom mud. It can besprayed from the bank or applied from aboat outfitted for chemical applications.It should be noted that excessivewater flow through ponds flushes plantnutrients from the water, favoring rootedweeds that can obtain nutrients frombottom soils. Ponds should not havewatershed areas larger than necessary tomaintain water level; excess runoff fromlarge watersheds should be divertedaway from ponds. Springs running intoponds can also dilute nutrients, and theytoo can be diverted away from the pondand can be allowed to enter the pondonly when water is needed.Manual harvesting. Removingpotentially noxious emergent weeds byhand is another management practicethat may reduce the possibility of havingto use chemicals. As small areas of thepond margin become infested, plants areremoved manually. Manual harvestingof weeds is only suited for controllingemergent vegetation in relatively smallponds. Care should be taken to removeas much of the rootstock or rhizome aspossible to minimize re-growth.Mechanical removal of filamentousalgae or submersed plants almost alwaysproves to be futile.Routine mowing of pond bankswill help prevent the establishment ofdense growths of shoreline plants suchas willows and will also reduce habitatfor snakes.10

Water draw-downs. Periodicwater draw-downs are sometimeseffective in killing or preventing aquaticweeds. The vegetation along the pondmargin (the most common location forweed problems) is stranded and diesfrom drying up.Biological control of aquaticplantsBiological weed control in pondsinvolves the use of fish to consumeunwanted aquatic vegetation. Grass carpare normally used in warmwater ponds.They are most often used to controlsubmersed plants or filamentous algae.Koi (colorful common carp, Cyprinuscarpio koi) are presently being evaluatedat Kentucky State University for theirweed prevention potential.Grass carp. The grass carp or“white amur” (Ctenopharyngodon idella,Figure 17) was introduced into theUnited States from Southeast Asia in1963 and is now widespread especiallyin the southeastern states. The fish isbanned in many states and some statesallow only sterile, triploid grass carp.Where legal and available, this fish is avaluable tool to control nuisance aquaticweeds.Figure 17. Triploid grass carp fingerling(Ctenopharyngodon idella).The controversy over thedistribution and use of grass carp isbased on the potential effect of this fishon native fish and wildlife.Considerable discretion shouldbe used when planning to stock thesefish into ponds and every effort shouldbe made to prevent their escape intonatural waters. To further diminish thelikelihood that that grass carp willreproduce and thrive in natural waters, itis recommended that only sterile, triploidcarp be used.The grass carp has several traitsthat make it a good species forrecreational ponds and for polyculturingwith channel catfish. Small grass carp(less than 1-2 pounds) are almostcompletely herbivorous and will notcompete to a significant degree withcatfish for feed. Grass carp tolerate awide range of environmental conditions:they can survive at water temperatures of32º to 105º F and are nearly as tolerantas catfish to low dissolved oxygenconcentrations. The fish grows rapidly,as much as 5 to 10 pounds a year. Itmust consume large quantities of plantmaterial to grow and may consume 2 to3 times its weight in plant material perday.Grass carp prefer to eat succulentsubmersed plants such as Najas spp. andChara spp. Fibrous plants such asgrasses and smartweed are less preferredand grass carp will not eat these plants ifmore preferred plants are available.Food consumption by grass carp isgreatest at water temperatures of 80º to85º F, and the fish stops eating when thetemperature falls below about 55º F.In catfish nursery ponds, grasscarp should be stocked prior to stockingthe catfish fry in order to prevent weedgrowth. Likewise, in recreational ponds,11

grass carp should be stocked beforeweeds become a problem.Grass carp also are used by somepond owners to control existing weeds.However, considerable time is requiredfor grass carp to reduce weedinfestations, particularly if coverage isextensive. Results may take a year to berealized. Food-fish ponds are usuallynot drained each year and grass carpbecome a permanent inhabitant of thepond. Larger grass carp learn to feed onpelleted feeds and often do little tocontrol weeds in the second or third yearthey are present. Usually weedproblems have been controlled by thistime and a phytoplankton communityhas developed which prevents furtherweed growth.The stocking rate for grass carpdepends on the severity of the weedproblem. When used to prevent theestablishment of submersed weeds, 5-10small (3-6 inch) carp per acre should bestocked. The same stocking rate is alsoadequate if the pond is lightly infestedwith weeds. For more severe weedproblems, 10-15 fish per acre should bestocked. For heavily weed infestedponds, stocking rates can be increased to15-25 per acre or greater. Grass carpmust be stocked at a size large enough toprevent them from being eaten bypredator fish such as bass and largecatfish.Koi. Koi have been shown toreduce the occurrence of submersedaquatic weeds and filamentous algae bykeeping pond water turbid. The turbiditymay be caused by their activity in thepond bottom which keeps the mudsuspended in the water column andreleases nutrients, supplying a foodsource for the phytoplankton bloom. The“rooting-around” on the pond bottomalso prevents weeds from establishingthere. Koi have been chosen foruniversity demonstration projects overnon-colorful common carp because ofthe side benefits of having an attractiveaddition to the pond and a fish that canbe marketed for its ornamental value(Figure 18). Cover photographs illustrateponds without koi (front cover) andponds with koi (back cover) at KentuckyState University Aquaculture Center.Figure 18. Koi keep pond water turbidwhich reduces the occurrence ofnuisance aquatic weeds.Control of aquatic plants withherbicidesControl of aquatic weeds withherbicides is the most common means oferadicating weeds in ponds. Correctidentification of weeds is criticalbecause potential impacts andmanagement differ for each plant.Strategies effective on one species maybe ineffective even on similar species. Inparticular, herbicides are selective (somemuch more than others), and effectivecontrol depends on matching the weedwith the most appropriate herbicide.Private consultants or experts at localuniversities can help identify the weedproblem.In the United States, registrationof chemicals for fishery use is granted12

y the Environmental Protection Agencyor the Food and Drug Administrationunder the Federal Environment PesticideControl Act (FEPCA) of 1972. The lackof registration does not necessarily meanthat the chemical is harmful to theenvironment or that it is extremely toxic.Aquaculture is considered a minor useby most chemical companies, and theyare simply not willing to spend the largeamount of money needed to compile thedata necessary for registration review.However, some unregistered herbicidesare toxic to fish or their use may result inchemical residues in the edible portionof the fish. For these reasons, onlyherbicides labeled for use in food-fishponds should be used by pond owners,and label instructions should be carefullyfollowed. Proper chemical usage canalso minimize the effects on non-targetorganisms inside and outside the pond.Skin and eye protection should be wornwhen working with all chemicals toprevent absorption into the body.The following herbicides orherbicide groups are labeled for use infood-fish ponds. The tables on pages 22and 23 summarize herbicide use forcommon weeds in fish ponds.Copper sulfate (various tradenames). Copper sulfate (CuSO 4 ∙5H 2 O;copper sulfate pentahydrate) is availablein various particle sizes from finepowder to large crystals. The finepowder is more effective because itdissolves faster. Copper sulfate shouldonly be used to control algae, becauserates necessary to kill other plants mayalso be toxic to fish. The filamentousalgae, Pithophora spp., is resistant tocopper sulfate. Most algae arecontrolled more effectively if treatmentwith copper sulfate is made soon afterplant growth has started.In soft waters of low alkalinity,copper is extremely toxic to fish and it isrecommended that copper sulfate not beused in waters with a total alkalinity ofless than 50 parts per million (ppm) asCaCO 3 . Copper sulfate is less effectiveas an algicide in hard, alkaline watersbecause the copper rapidly precipitatesout of solution. The treatment rateincreases with total alkalinity, and theformula used to calculate the treatmentrate is:ppm copper sulfate = (ppm totalalkalinity) ÷ 100.In waters with a total alkalinity greaterthan about 300 ppm as CaCO 3 , copperfrom copper sulfate precipitates out ofsolution so rapidly that it is difficult toachieve an effective treatment.Use of copper sulfate can lead todangerously low oxygen concentrations,especially in the summer. When treatingfilamentous algae, the danger of lowdissolved oxygen concentrationsfollowing treatment can be minimizedby treating 1 / 3 to 1 / 2 of the water area at atime and waiting 10 to 14 days betweentreatments.Dissolve the number of poundsof copper sulfate to be used in at leastthe same number of gallons of waterbefore applying to the pond (forinstance, dissolve 10 pounds of coppersulfate in 10 gallons of water). It is bestto apply copper sulfate in clear waterabove 60º F and on a sunny day. Itshould also be noted that putting coppersulfate solution in galvanized containerscauses the copper to chemically displacethe galvanized lining. This removescopper from the treatment solution.Chelated copper (Cutrine-Plus,Clearigate, Cutrine-Ultra, K-Tea,Algimycin, Komeen, Pondmaster,Nautique, Captain). These herbicidesare available in both liquid and granular13

form, but the liquid is most commonlyused. The copper in these herbicides isbound in organic complexes so that thecopper will not precipitate out ofsolution as rapidly as uncomplexedcopper in hard, alkaline waters. Cutrine-Plus, for example, has a prolongedeffectiveness because its chelating agent,ethanolamine, decomposes slowly insunlight. Although chelated copperherbicides usually are more effectivethan copper sulfate, they areconsiderably more expensive to use.The table on page 21 of this booklet liststhe aquatic weeds controlled by each ofthe chelated copper compounds. Copperherbicides have a reputation foreffectively killing algae includingphytoplankton, some filamentous algaeand Chara (musk grass) which is also analgae. However, Cutrine-Ultra isspecially designed to kill Pithophorawith a penetrating surfactant. AndKomeen, Pondmaster, Nautique, andCaptain, unlike many other chelatedcoppers, are able to control higheraquatic plants like Najas, coontail,Elodea and sago pondweed.Additionally, chelated coppersare often combined with other herbicidessuch as Reward, Aquathol, or Sonar toenhance their effectiveness, and in somecases, reduce the amount needed of bothherbicides.Diquat (Reward, Weedtrine D).Diquat is sold as a liquid containing 2pounds active ingredient per gallon. It isa wide-spectrum herbicide and willcontrol most filamentous algae includingPithophora spp. and Chara spp.,submersed weeds such as Najas spp. andcoontail, and can be mixed with asurfactant and sprayed to controlemergent weeds such as cattail. Diquatshould not be used in muddy water andmud should not be stirred up duringapplication because diquat will bindtightly with clay particles suspended inthe water rendering the herbicideineffective at controlling plants growingbeneath the surface. Diquat should beapplied on a sunny day to activelygrowing weeds. Only 1 / 3 to 1 / 2 of thepond water area should be treated at onetime with a 14-day interval betweentreatments. A 14-day withdrawal periodis required by law after diquat use beforetreated water can be used for animalconsumption, swimming, spraying,irrigation or drinking.Endothall, dipotassium salt(Aquathol, Aquathol K, AquatholSuper K). The dipotassium salt ofendothall is available in liquid (AquatholK) or granular (Aquathol) form. It willnot kill algae but will control a widevariety of submersed higher plants,including Najas spp., coontail, andfanwort. The granular formulation isrelatively expensive, but is particularlyeffective on Najas spp. Dipotassium saltof endothall is a contact killer. It issprayed onto or injected below the watersurface and can be sprayed at highconcentrations directly on exposedweeds. For best results, watertemperatures should be 65º F or above.When water temperatures are high andan increased danger of dissolved oxygendepletion exists, this herbicide should beapplied to 1 / 3 to 1 / 2 of the pond pertreatment with a 5 to 7 day intervalbetween treatment applications.Water treated with granularAquathol must not be used for irrigationor for agricultural sprays on food cropsor for domestic purposes within 7 daysof treatment. More detailed restrictionsexist for Aquathol K. It may not be usedfor the above mentioned purposes aswell as for watering livestock for 7 daysafter applying it up to 0.5 ppm; for 1414

days after application up to 4.25 ppm;and for 25 days after application up to5.0 ppm. In addition, water treated withAquathol K may not be used forswimming until 24 hours after treatment.Endothall, alkylamine salt(Hydrothol 191). The alkylamine saltof endothall (Hydrothol 191) is mostcommonly used in the liquidformulation. It is a more potentherbicide than the potassium salt(Aquathol K) and will control mostfilamentous algae including Pithophoraspp. and Chara spp. Repeat treatmentsare recommended if algae growthreappears. Hydrothol 191 is a relativelytoxic herbicide to fish and treatmentrates required to treat submersed higherplants are generally too risky incommercial catfish ponds to justify itsuse. When the herbicide is used to treatfilamentous algae, only a portion of thepond should be treated at one time. Fishavoid the treated area and are usually notkilled. Hydrothol 191 treatments as highas 0.3 ppm (often needed to killPithophora spp.) can be used, but higherrates will kill fish.Fish in treated waters may not beconsumed within 3 days after treatmentwith Hydrothol 191. Likewise, treatedwater should not be used for wateringlivestock, preparing agricultural spraysfor food crops, irrigation, or domesticpurposes within 7 days after applicationwhen up to 3.0 ppm Hydrothol 191 isused.Fluridone (Sonar, Avast).Fluridone is available as an aqueoussuspension or as slow-release (SRP),precision release (PR) and quick releasepellets. Fluridone will not killphytoplankton or filamentous algae, butcontrols a broad spectrum of submersedhigher plants. This herbicide is slowacting, and results may take 30 to 90days to be noticeable. The slow killingaction (and thus slow weeddecomposition) helps to prevent lowdissolved oxygen that typically resultsfrom rapidly decomposing weeds.Usually within 7 to 10 days of treatmentthe growing points of treated plantsbecome white or pink as a result ofchlorophyll photo degradation. Sonarshould be applied to actively growingweeds, and the entire pond surfaceshould be treated at once. Partial or spottreatments result in dilution of theherbicide with the untreated water. Donot use treated water for crop irrigationfor 30 days after application.2,4-D (Aquacide, Aqua-Kleen,Weed-Rhap, Weedtrine II, etc.). Thisherbicide is formulated for aquatic use asthe dimethylamine salt or isooctyl ester.It is available in liquid or granular form.The granular form is effective atcontrolling submersed higher plants suchas Najas spp. and coontail. The liquidformulations of 2,4-D are most effectivein spring when weeds start to grow.Acid pH (6 and below) enhances itsherbicidal activity while a pH of 8 orabove tends to make it less effective.Treating early in the morning when pHis usually lowest will increase theeffectiveness of 2,4-D.Glyphosate (Rodeo,Aquamaster, AquaPRO, etc.).Glyphosate is sold as a liquid and is foruse mostly on emergent and shorelineplants. The herbicide is mixed with asurfactant and sprayed on the vegetation.Glyphosate is a broad spectrumherbicide and is useful for the control ofcattails, grasses, smartweed, and willowsaround pond margins. Application whenweeds are in the flowering or fruitingstage is more effective than earlierapplication. Visible results (wilting andyellowing) are usually not seen for 2 to 715

days after application. Rainfalloccurring within 6 hours of applicationreduces the effectiveness of Rodeo.Imazapyr (Habitat, AquaPier).Imazapyr is a liquid herbicide that ismixed with water and a surfactant orvegetable oil and sprayed on emergent orfloating aquatic weeds. When sprayeddirectly onto emergent leaves, theherbicide is translocated throughout theweed, concentrating in the roots where itcauses the weed to die (which sometimestakes more than two weeks) and preventsfuture re-growth. Imazapyr is mosteffective if applied when the weed isactively growing. The effectiveness ofimazapyr is reduced if it rains within anhour of application. The label notes that“Habitat does not control plants whichare completely submerged or have amajority of their foliage under water.”Due to the risk of oxygendepletion from decomposing weeds, nomore than half the pond’s surface areashould be treated at one time, and atleast 10 to 14 days should separatetreatments. An applicator’s license isrequired to purchase and applyimazapyr. The most current herbicidedirections (found in the leaflet labelattached to the container) shouldoverride any other treatment advice,including that found in this booklet.Imazapyr is relativelyenvironmentally safe. Treated watershave no restrictions for recreationincluding swimming and fishing or forlivestock consumption. However,imazapyr may not be applied to waterwithin one-half mile upstream of anactive potable water intake.Triclopyr (Renovate 3,Renovate OTF, Garlon 3A). Renovate3 is a liquid herbicide used to controlcertain emergent, submersed andfloating aquatic plants (includingalligatorweed, milfoil, waterhyacinth,waterlily, and waterprimrose) in bodiesof water that have little or no continuousoutflow. Mixing triclopyr with a nonionicsurfactant is recommended toimprove its effectiveness.Renovate OTF (On TargetFlakes) settles directly on submersedweeds and, therefore, is effective atlower concentrations than liquidRenovate 3. (60% less active ingredientcan be used when applying RenovateOTF, making it more environmentallyfriendly).Triclopyr treated water shouldnot be used for irrigation for 120 daysunless the triclopyr is not detectable bylaboratory analysis. The most currentherbicide directions (found in the leafletlabel attached to the container) shouldoverride any other treatment advice,including that found in this booklet.Penoxsulam (Galleon SC).Galleon SC was approved for use as anaquatic herbicide on July 17, 2007. Itcontrols duckweed, water hyacinth,cabomba, egeria (elodea), Eurasianwatermilfoil, hydrilla and sagopondweed.Galleon SC partially controlsweeds in the following list. Dependingon dosage, time of year, growth stage,application method and degree of watermovement, the weeds listed above canbe controlled while leaving thefollowing native species unharmed. (Orhigher treatment rates can be used tocontrol weeds in both lists). Partiallycontrolled weeds include watermeal,alligatorweed, arrowhead, parrotfeather,smartweed, pondweed, najas andspikerush.A surfactant must be added whenemergent weeds are being controlled. Aswith Sonar, Galleon SC is very slowacting and should be applied to the entire16

pond surface at once. (Partial or spottreatments result in dilution of theherbicide with the untreated water).Galleon SC also can be applied as a preemergentin empty (dewatered) ponds.Check a current label to get the exacttreatment rate for each type of weed.Sodium CarbonatePeroxyhydrate (GreenCleanPRO,Phycomycin, Pak 27). SodiumCarbonate Peroxyhydrate (percarbonate)is a granular algaecide/fungicide used totreat, control and prevent a broadspectrum of algae and fungi. For themost effective treatment, usepercarbonate when algae growth firstappears, and treat early in the day whensunny with little or no wind. Floatingalgae mats should be broken up beforeor during treatment; and after treatment,dead algae can be removed from thewater surface to prevent excessivenutrients from entering back into thewater (during decomposition) andstimulating subsequent heavyphytoplankton blooms. The BioSafeSystems’ technical bulletin points outthat GreenCleanPRO has no restrictionsfor use after treatment and it is labeledfor use in aquaculture. Planktonic bluegreenalgae blooms are treated with 9 to30 lb per acre-foot of water; the exactamount needed depends on the quantityof algae growth, light intensity, andwater quality. The most currentdirections (found on the container)should override any other treatmentadvice, including that found in thisbooklet.The following web site has labelsfor the aquatic herbicides mentionedabove:http://aquat1.ifas.ufl.edu/guide/labmsds.htmlAnother helpful web site ishttp://www.appliedbiochemists.com/products.htmCarefully follow herbicide labelsHerbicides sold in the UnitedStates must be registered with federaland state regulatory agencies. Theprinted information accompanying theherbicide container is called the “label”and constitutes a legal document. Failureto use herbicides according to labelinstructions can lead to severe penalties.From a practical standpoint, misuse ofherbicides can result in poor weedcontrol; risks to people, fish, or wildlife;or herbicide residue problems in fish.The label provides informationon the active ingredient, directions forcorrect use on target plant species,warnings and use restrictions, and safetyand antidote information. Remember,state and local regulations may be morerestrictive than federal regulations.Certain products are registered as“Restricted Use” herbicides and can belegally applied only by trained andcertified applicators or by people undertheir direct supervision. Be sure to checkfederal, state, and local regulations priorto using herbicides.Herbicide treatment rates arebased on pond area or pond volume.Miscalculation will result in either overtreatmentor under-treatment (which mayrequire additional treatments to eradicatethe weed). In either case, more chemicalthan needed will be applied to the pond.Carefully measure pond dimensions andkeep up-to-date records of pond size anddepth. Pond depth tends to decrease overtime because of erosion of embankmentsand sedimentation of pond bottoms. Theonly way to be certain of average ponddepth is to measure water depth beforetreatment at several dozen randomlocations.17

Handle herbicides safelyAlthough aquatic herbicides arerelatively safe to handle, it isnevertheless important for applicators tokeep chemical exposure to an absoluteminimum. Herbicide labels and materialsafety data sheets advise what protectiveclothing and equipment should be worn,any precautions the handler shouldfollow, a statement of practical treatmentin case of poisoning, statementsconcerning hazards to the environment,any physical or chemical hazards, anddirections on proper storage anddisposal. By law, copies of labels andany supplementary labels must be in thepossession of the applicator at theapplication site for each herbicide used.Anyone who handles a pesticide mustread and understand all label statementsprior to using the product. Herbicidesafety is reviewed in SRAC publication3601 which can be found atwww.msstate.edu/dept/srac .Dispose of herbicide containersproperlyImproper disposal of herbicidecontainers can cause contamination ofsoil and water, and may result in fines orloss of an applicator’s license. Emptyherbicide containers must be triplerinsed, with each rinsing drained into theherbicide mix tank. If no mix tank isused, the rinse water from the containershould be applied to the pond in thesame manner as the herbicide in thecontainer. Containers must then bepunctured or crushed so that they can notbe reused. Empty bags must be rinsed orshaken clean and cut so that they can notbe used for other purposes. Lawsregarding disposal of rinsed containersvary among states, so be sure to followall state and local regulations regardingpesticide container disposal.Two aquatic herbicides, 2,4-Dand endothall, are regulated as hazardousmaterials under federal law, and anywaste generated during their use must bedisposed of as hazardous waste. Triplerinsedcontainers can be disposed of aswith any other pesticide container. Anyrinse water from cleaning of containersor application equipment must beapplied as if it were the herbicide ordisposed of at a hazardous wastedisposal facility.Consequences of herbicide useWhen used according to themanufacturer’s specifications, herbicidesare seldom directly toxic to fish.However, the addition of any herbicideto a plant-infested body of water willalter water quality. Oxygen productionby photosynthesis will be decreased anddecomposition of the dead plant materialwill increase oxygen consumption. Theresult will be a noticeable decrease indissolved oxygen concentrationscompared to pretreatment levels. Theextent to which dissolved oxygen levelsare reduced depends on the amount ofplant material killed, the amount of plantmaterial unaffected by the herbicide, therate that death occurs, water temperatureand other factors. Decomposition of thedead plants will also raise carbondioxide and total ammoniaconcentrations. The increase in totalammonia concentrations tends todecrease the pH, causing much of theammonia to be in the non-toxic, ionizedform. Phosphorus, potassium, and otherminerals are also released upon plantdecomposition, and concentrations of allessential plant nutrients will usually behigher after herbicide treatment. Atsome time after treatment, theconcentration of herbicide will decrease18

to a non-toxic level and these nutrientswill be available for new plant growth.The deterioration in water qualityfollowing herbicide use can have seriousconsequences in catfish ponds.Obviously, if dissolved oxygenconcentrations fall to very low levels,fish will be killed. This is particularly aproblem in catfish fry ponds because fryoften cannot find the area of aeratedwater behind emergency aerators. Evenif dissolved oxygen concentrations aremaintained above lethal levels, the fishmay be severely stressed and moresusceptible to fish diseases.Stressed fish also feed poorly anddecreased fish growth can be expected,particularly if water quality is affectedfor an extended length of time.Control of phytoplanktonabundanceLow concentrations of dissolvedoxygen and development of off-flavorare the most important water qualityproblems in channel catfish pondculture. Both problems are the result ofuncontrolled phytoplankton growth inheavily fed ponds. Numerous effortshave been made to managephytoplankton communities in fishponds, but most methods are ineffectiveand many actually further degrade waterquality.A variety of algaecides havebeen used to reduce phytoplanktondensity, but the ultimate results arealways undesirable. When sufficientalgaecide is added to a pond with adense bloom, the sudden die-off usuallycauses severe oxygen depletion and highlevels of carbon dioxide and ammonia.Phytoplankton repopulate the pond assoon as algaecide levels decreasebecause nutrient levels remain high.Episodes of poor water quality resultingfrom this cycle of death and regrowthwill stress fish and cause reduced growthor increased susceptibility to infectiousdiseases. Similar problems occur whenalgaecides are used in attempts toeliminate specific noxiousphytoplankton species. All of theeffective algaecides registered for use infood fish ponds are broad spectrum inactivity and cannot be used to selectivelyeliminate one species or one type ofphytoplankton.Biological control ofphytoplankton growth is an alternative tothe use of herbicides. Most efforts haveinvolved the use of plankton-feeding fishsuch as silver carp, bighead carp, ortilapia. In theory, the plankton-feedingfish continually harvests the bloom,improves water quality, and providesadditional fish production. However,most attempts at biological control ofphytoplankton growth have failed. Quiteoften phytoplankton abundanceincreases when plankton-feeding fish arepresent because these fish effectivelyremove large phytoplankton andzooplankton which compete with orconsume small phytoplankton. Thepresence of plankton-feeding fish maythus change the structure of the planktoncommunity, but usually will not decreaseoverall phytoplankton density.Decreasing nutrient levels bylimiting daily feed allotments is the onlyreliable method available for reducing,on average, the incidence ofphytoplankton-related water qualityproblems. Such problems are rare ifmaximum daily feeding rates are lessthan about 50 pounds per acre, but thisfeeding rate is uneconomical in mostcommercial enterprises.19

Copper-based Herbicides Trade Name Effective AgainstCopper sulfate pentahydrate Various names Planktonic algaeFilamentous algae except for Pithophora sp.Chara sp. (musk grass)Mixed copper-ethanolamine complexesMixed copper-ethanolamine complexes in anemulsified formulation .Contains an emulsified surfactant/penetrant forhighly effective control of coarse (thick cell-walled)filamentous algae – Pithophora sp.Cutrine ® -PlusClearigate ®Cutrine ® -UltraPlanktonic algaeFilamentous algaeChara/NitellaHydrillaPlanktonic algaeFilamentous algae including PithophoraChara/NitellaHydrillaEgeriaCopper-triethanolamine complex and copperhydroxideK-Tea ®Green algaeBlue-green algaeDiatomsFlagellated protozoaCopper citrate and copper gluconate Algimycin ® Planktonic algaeCopper-ethylenediamine complex and coppersulfate pentahydrateKomeen ®Pondmaster ®Copper carbonate Nautique ®Captain ®Filamentous algae except for Pithophora sp.HydrillaWaterhyacinthEgeriaElodeaNajasCoontailWatermilfoilSago PondweedAmerican PondweedWater LettuceControls all of the above plants controlled byKomeen ® and also controlsCurlyleaf pondweedHorned pondweedThin Leaf pondweedVallisneriaWidgeon grass21

Aquatic group &vegetationCopper sulfateand somechelated coppercomplexesCutrine-UltraKomeenPondmasterNautiqueCaptain2, 4-D Diquat Aquathol Hydrothol Glyphosate Fluridone Triclopyr Imazapyr Sodium carbonateperoxyhydrateAlgaephytoplankton E E P P G P P Gfilamentous algae E E P G P G P P GPithophora spp. G Gmuskgrass (Chara E E P P P G P Pspp.)Floating plantsduckweeds P F G P P P E Fwater hyacinth P G E E G E E Ewatermeal P F F GSubmersed plantscoontail P G G E E Emilfoils P G E E E G Enaiads P G F E E Epondweeds P G P G E E G 1Emergent plantsalligatorweed F P G F E Earrowhead P E G G E E Ecattails P F G P E F Esedges & rushes P F F G P E 2 F 3slender spikerush P G P G Fsmartweed P F E F E F E Ewaterlilies P E P G E G Gwater primrose P E F P E F E Ewatershield P E P G G Ewillows P E F P E P E EE = excellent control, G = good control, F = fair control, P = poor control, blank = unknown or no response 1 Spray only emergent portion, 2 E for sedge, 3 F for rush Table from SRAC 3614

ProductCommon Trade NamesCopperCopper sulfate, Cutrine-Plus, Aquatrine, Clearigate, Cutrine-Ultra, K-Tea, Algimycin, Komeen,Pondmaster, Captain, NautiqueEndothall Aquathol, Aquathol K, Aquathol Super K, Hydrothol 191Hydrothol Hydrothol 1912, 4-D Navigate, WeedRhap, Weedar 64, Aqua-KleenFluridoneDiquatGlyphosateTriclopyrImazapyrSodium carbonateperoxyhydrateSurfactantDyesSonar, Sonar AS, Sonar PR, Sonar SRP, Sonar Q, SonarOne (expected spring 2008), Avast,Avast SRPReward, Weedtrine DRodeo, Aquamaster, AquaPRO, AquaNeat, Eraser AQ, Eagre, Glypro, AquastarRenovate 3, Renovate OTF, Garlon 3AHabitat, AquaPierGreenClean, GreenCleanPRO, Pak 27, PhycomycinCide KickAquashade, Aquashadow, Admiral Liquid, Admiral WSP5

January 2008, Kentucky State University Aquaculture Program,a KSU Land Grant Program20