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

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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
Page 1 and 2: Aquatic Weed Control in PondsRobert
Page 3 and 4: Aquatic Weed Control in PondsBob Du
Page 5 and 6: Figure 6. The filamentous algae,Pit
Page 7 and 8: Polygonum spp. (smartweed) - leaves
Page 9: Prevention of aquatic weedsAlmost a
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
Page 24: January 2008, Kentucky State Univer

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

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