Aquatic Weed Control:When Every Drop Counts

As water becomes more preciouseach year, the sports turf managermust consider surface water as more

than "aquascapes," lagoons or recreationalsites. Every drop must be protected frommisuse or waste.

Droughts, as we have seen this summer,can strike anywhere at any time. The newsmedia pays great attention to the impactof droughts on agriculture, but very littleattention to their impact on the multi-billiondollar sports turf industry. Farmers can dolittle to counteract a drought. Sports turfmanagers, on the other hand, have a short-term solution in lakes and ponds if they planahead and keep surface water in conditionfor irrigation. That entails regular aquaticweed control and lake management.

While the original justification for build-ing lakes and ponds is usually both aes-thetic and functional, the combination of thetwo has never been stronger. Any body ofwater built for flood control, wildlife, swim-ming and appearance, must also be treatedas a potential bank for water when droughtor water restrictions occur.

Today, as in frontier days, water rightsare something worth fighting for and pro-tecting at all costs. Instead of rancher fightingagainst rancher for limited water, the bat-tle today is between water agencies tryingto meet the demand of residential and indus-trial growth ... and golf courses, parks andother recreational facilities.

When the chips are down, the only wateryou can really count on is that water heldin reserve on your property. Water flowingin rivers through your facility or pumped bywells from subsurface aquifers may not beat your disposal in times of shortage. Onlyyou really appreciate the value of water toyour sports turf. Leaving the decision ofwater availability during shortages up to apublic agency places your facility at seri-ous risk. You simply can't count on havingwater during droughts unless it is in reser-voirs under your direct control.

Aquatic management should definitely bepart of a water shortage plan. Facilities indrought-prone areas should invest no lessin aquatic weed control and lake manage-ment than they do in efficient irrigation andpumping systems, drought-tolerant turf-grasses or water-conserving redesign. No

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Floating and emergent weeds clog golf course pond. Photo courtesy: Monsanto.

Same pond following treatment with glyphosate. Photo courtesy: Monsanto.

July, 1988 15

Aquatic Weed Controlcontinued from page 15

amount of efficiency is important if your watersource is inadequate.

To complicate matters further, liabilityassociated with lake management is a deter-rent rather than an endorsement of wisewater storage. In many cases, proper aquaticweed management requires treatment withchemicals and lake aeration. Insurance com-panies are sensitive to the potential for con-tamination, electrocution, or drowning. Theyindirectly penalize those parks, golf coursesor sports facilities with lakes by charginghigher premiums. For this reason many facil-ities contract out water treatment to trans-fer part of their liability to the contractor.

Realistically, it's doubtful if any facility canstore enough water in surface reservoirswhen an irrigation system requires millionsof gallons per week. However, one acre-foot of water represents 325,829 gallons youmight not have otherwise. That is enoughto irrigate a regulation size football field fornearly six weeks (1112 inch per week) or 18average size golf greens for three weeks(2 inches per week). But it pales in com-parison to the two million plus gallonsneeded by 50 acres of fairways each weekduring the growing season. For totalindependence from outside water sourcesan 18-hole golf course would need sevenacre feet of water per week, or the equiva-lent of a seven-foot-eleep, one-acre lake eachweek. It makes you extremely grateful forrainfall even though it may cause a golfcourse to lose rounds or a game to be can-celled.

The value of surface water has never beengreater than it is today. Allowing reservoirsto become choked with aquatic weeds orcovered with algae blooms not only ruinstheir aesthetic value, it destroys their func-tional value as well. Algae can be transportedfrom infested lakes through irrigation linesto turf. Parts of vascular aquatic weeds canenter intakes, go through pumps and endup anywhere irrigation water is distributedif the water is not filtered or screened. Likeany weed, once it becomes establishedwithin the boundaries of a sports facility,it places "weed pressure" on the remainderof the facility.

A sports turf manager needs to under-stand that a lake or pond left unattendedwill go through a natural progression thatfills it in over time. Water- and air-bornedebris gradually reduces the depth of lakesand isolates them from one another. As lakesbecome shallower, bottom-rooted aquaticplants flourish by taking advantage of sun-light penetrating the top few feet of water.Waterfowl deposit seeds to establish shore-line vegetation which blocks air circulationat the surface and serves to hide insect lar-vae from fish and other natural predators.

As the lake becomes overloaded withvegetation, wind is unable to create wavesor a current to circulate oxygen from thesurface and cool water from the bottom.Without oxygen, plant material can't decom-pose properly and fish can't live. During

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anaerobic decomposition, microorganismsrelease foul-smelling odors. Finally, the coldwater at the bottom becomes trapped andthe temperature of the surface water rises.This phenomenon, called stratification, cantrigger an algae bloom as surface water tem-peratures reach optimum levels for algalgrowth.

When a sports turf manager applies sixor more pounds of nitrogen per 1,000 squarefeet per year and two inches of water perweek to turf surrounding lakes, part of thenitrogen in the watershed can reach the lakeenriching the production of aquatic vege-tation. This speeds up natural progressionand lake decline unless measures are takento stop it.

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:G'ti;&a~~.~Lake before and after treatment with tlundone,Photo courtesy: Elanco.

To really get control over aquatic plantmanagement you have to start at the bot-tom. The more shallow area there is in alake or pond, the more aquatic weedproblems you'll Have. Aquatic plants maybe desirable in certain locations. These sitescan be shallow. But the remainder of thelake should be eight or more feet deep todiscourage the establishment of bottom-rooted weeds. Lakes with gradually slop-ing banks will have more weed problemsthan those with steeper banks. The shore-line should be stabilized with rock, gabionbaskets, jute or geotextile to prevent ero-sion until vegetation is established. Treesor shrubs with extensive root systems shouldnot be planted near the edge of reservoirs.Their roots may eventually break throughthe water barrier. If chemical control of thelake becomes necessary later, these rootsmay absorb some of the herbicide intendedfor the aquatic weeds.

Lake bottoms should be tightly sealed withimpervious liners or packed bentonite clay.The clay swells when wet to form a water-tight barrier. Core tests are frequentlyadvised to locate any layers of sand or rockin the area which could lead to rapid lossof water.

The ultimate lake has a drainage outlet

and/or weir to control the water level. Onemethod of aquatic weed control is to drawthe lake level down to expose weeds to des-sication or cold winter temperatures. If draw-down is a possibility, a deep pocket shouldbe provided in the lake bottom as a tem-porary home for fish. An irrigation intakeleading to a filter system should be installedin any sizeable pond or lake.

Today, many sports facilities with lakesare taking an extra step to improve oxygenlevels and to prevent stratification. They areinstalling aerators which either pump waterinto the air where it can take on oxygen orinject air into the lake. The action of the aer-ators creates a flow that constantly mixesthe water in the lake. By keeping surfacewater cooler and preventing the buildup ofnutrient levels in lakes, aerators can pre-vent and in some cases correct algaeblooms.

Water treatment plants have used aera-tors for decades to improve bacterial decom-position of organic materials in water. Theoxygen added to the water favors aerobicdecomposition over anaerobic (with itsunpleasant odors) and speeds upprocessing.

Fountain aerators provide an aestheticdimension to lake aeration by propellingwater into the air in an attractive display.Lights can be added to fountain aeratorsto extend their appearance benefits into thenight. Many aerators can be installed by thesports turf manager with the help of an elec-trician. Some lakes may require more thanone aerator. Check with manufacturers forspecifications on pumping capacity, energyconsumption and the mixing depth of theirvarious units.

The above measu res play a major rolein keeping lake water in suitable conditionfor irrigation. The key is knowing whendesirable aquatic vegetation growth startshurting the functional use of the lake or whenundesirable weeds become established. Noone wants a sterile, lifeless lake sitting inthe middle of their landscape: However,ignoring lake vegetation for months can leadto trouble.

There are four basic types of aquaticweeds - algae, floating plants, submersedweeds and emergent weeds. Sports turfmanagers for the most part can handle con-trol of algae and emergent weeds. Manychoose to hire aquatic weed specialists forcontrol of submersed or floating weeds.

Algae are very simple forms of plants.Serious outbreaks of algae can rob a lakeof oxygen causing fishkills, give off a muskyodor, plug up irrigation intakes and heads,and ruin the appearance of water features.Warm temperatures and water rich innutrients can bring on a "bloom" in a mat-ter of days.

Three types of algae are generally recog-nized. The first is called planktonic. Thesetiny microscopic plants can accumulate inthe top three to four feet of water giving ita green, soupy appearance. Filamentousalgae join together in mats, usually form-

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Aquatic Weed Controlcontinued from page 16

ing along the edge or banks of lakes. Thesemats grow in size and can rise to the sur-face in time. The third and most advancedtype of algae is called attached-erect. Theyappear like plants growing from the lake bot-tom, but they are not rooted. Often they arecalled chara, nitella, muskgrass or stonewortinstead of algae.

Fortunately, algae is very sensitive to cop-per in the water. Control efforts revolvemainly around keeping copper levels up astemperatures rise in the spring and sum-mer. Early treatment utilized copper sul-phate. Today, chelated forms of copper areavailable which release the metal slowly.Applications should be made periodicallyduring the growing season to maintain cop-per at control levels in the top four feet ofwater.

Emergent weeds are found along thebanks and shallow areas of lakes. They arerigid plants which support themselves outof water. Many are considered desirable andserve as habitat for fish, waterfowl andinsects. Cattail, arrowhead, bullrush, waterprimrose and purple loosestrife are emer-gent aquatic weeds when they spreadbeyond control.

Since emergent plants are above waterand near the shoreline, they can be con-trolled effectively with contact herbicidessuch as 2,4-0, Diquat, and glyphosate(Rodeo). A surfactant or sticker can be mixedwith these products to improve contact andcontrol. These chemicals will harm any plant

Gilbert advises thatearly treatmentavoids a heavy"biomass" and

protects some typesof desirable plants.

they contact so pay close attention to drift.Glyphosate is deactivated rapidly upon con-tact with muddy water or soil therefore thereis no time restriction on use of lake waterfollowing treatment. Diquat is deactivatedwithin 14 days. The water use delay for 2,4-0varies according to the specific formulationused.

Floating weeds have leaves that float onthe surface. They may float freely on thesurface or be rooted. Water lilies are float-ing plants that are sometimes planted inlakes for the appearance of their flowersand round leaves. Other floating weedsinclude water hyacinth, duckweed, waterpennywort, common salvinia, watershieldand water lettuce.

The fact that the leaves are on the sur-face provides a control advantage. Herbi-cides such as Diquat, glyphosate (Rodeo)and 2,4-0 mixed with a surfactant can beapplied to the leaves just as they would be

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for emergent weeds. Application is mosteffective on young or new foliage. Dich-lobenil and a new herbicide fluridone (Sonar)are also effective on floating weeds.Dichobenil's label carries a 90-day restric-tion on eating fish from a treated lake. Elancorecommends that water treated with fluri-done not be used for irrigation for 30 days.

Aquatic weed control becomes mostdifficult with submerged weeds. They includethe notorious hydrilla, watermilfoil, naiad,pondweed and coontail. These plants cannotsupport their own weight and depend uponthe water to hold them up. Small flowers,seed heads and fruit can extend above thewater surface. Foliage is close enough tothe surface for water fowl to feed on it.Stems, nutlets and seed can be carried bybirds to other lakes to spread infestations.

Since the plants are below the surfaceherbicides must be mixed with lake wateror applied as granules to be absorbed byfoliage or roots in the soil. Calculations mustbe made to determine the proper rates forthe volume of water in the lake, typicallymeasured in acre feet. Applications mustalso be made carefully to distribute the her-bicides equally throughout the treatmentarea. For these reasons, sports turfmanagers should consider hiring an aquaticweed specialist for submerged weed control.

In most areas, treatment of rivers andother flowing water is strictly the responsi-bility of a government agency. Managersof private recreational lakes without train-ing or certification specifically in aquaticweed control should not attempt treatment.

Diquat, f1uridone (Sonar), 2,4-0 formula-tions (i.e, Weedtrine II), endothal (Aquathol,Hydrothal191) are the primary herbicidesused for submersed weeds. Irrigation res-trictions range from 7 to 25 days for endothal.Timing of applications is important. Someselectivity may be possible through timing.This is a major marketing point for fluridone.

One concern over controlling denseinfestations of aquatic weeds is the amountof dead and decaying material in the waterand its drain on oxygen levels. Weeds canbe removed mechanically with special har-vesters if desired. The advantage to thismethod is the weeds are removed, but stemsand rhizomes below the cutting height mayregenerate into new plants. It is a com-promise to chemical control or may be usedin conjunction with follow-up herbicidetreatment.

Grass carp are another option to chemi-cal control. These sterile fish feed on sub-merged aquatic weeds. Ten to 20 carp cancontrol these weeds in an acre of lake. Theywill feed on floating and some emergentweeds if there are not enough submersedweeds for them. For this reason, they shouldnot be placed in lakes which contain desira-ble plants.

Lake dyes can be added to small lakesthat are too shallow to prevent establish-ment of algae and weeds by robbing themof sunlight. These non-toxic colorantsalso carry no water use restrictions.

Charles Gilbert, president of Allied Bio-

logical, an aquatic weed control contrac-tor in Gladstone, NJ, advises sports turfmanagers to treat weed problems early inthe year, beginning in April in his state. Thisway the sports turf manager avoids a heavy"biomass", after control and has free useof the water for irrigation during the hottesttimes of the year. Early treatment can alsoprotect some types of desirable plants.

Hydrilla has spread as far north as Dela-ware and Virginia, says Gilbert. Sports turfmanagers in those states and south shouldbe on the alert for the fast-spreading weedand begin control measures without delay.Hydrilla pieces on boat props or trailers canbecome serious infestations in the next lakethe boat is placed in.

"People arebecoming more

interested in selectivecontrol of aquatic

plants. "He adds that aerators are helpful in algae

control and decomposition of dead vascu-lar weeds in the top few feet. Beneath thatlevel, submersed aeration units can be used.Gilbert advises that chelated copper algae-cides are more effective than copper sul-fate in hard water with a high pH.

In the South, sports turf managers starttreating lakes in January, reveals DavidTarver, aquatic weed specialist for Elancoin Tallahassee, FL. One of the advantagesof fluridone (Sonar), the new aquatic her-bicide Tarver sells, is that it works over a30 to 90 day period to help the lake manageravoid large amounts of dead vegetation ina lake at anyone time. "People are alsobecoming more interested in selective con-trol of aquatic plants," he adds.

The other new aquatic herbicide that isimproving aquatic weed control is glypho-sate (Rodeo). It provides control of emer-gent weeds and shoreline brush without anyrestrictions on water use.

Few sports turf managers in the Southattempt major aquatic weed control any-more, says Tarver. "When lake water is usedfor irrigation the superintendent can't riskmaking a mistake. He has to control aquaticweeds, but he'd rather focus his efforts onwhat he knows best, turf, and let a specialistconcentrate on aquatic weeds - as longas weed control doesn't get in the way ofturf management."

Controlling aquatic weeds and protect-ing irrigation reservoirs will be more closelylinked in the future. The turf must come first,but every gallon of water must be ready forirrigation when droughts strike. Lakes mustbe maintained in the event of such unpredic-table shortages. Each acre foot of water instorage can provide weeks of green, play-able turf when all other water sources areshut down. That's something worth seriousconsideration. 0