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

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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
Page 1 and 2: Aquatic Weed Control in PondsRobert
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Page 5 and 6: Figure 6. The filamentous algae,Pit
Page 7: Polygonum spp. (smartweed) - leaves
Page 11 and 12: Water draw-downs. Periodicwater dra
Page 13 and 14: y the Environmental Protection Agen
Page 15 and 16: days after application up to 4.25 p
Page 17 and 18: pond surface at once. (Partial or s
Page 19: to a non-toxic level and these nutr
Page 22 and 23: Aquatic group &vegetationCopper sul
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Aquatic Weed Control in Ponds - Aquaculture at Kentucky State ...

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