low tunnel strawberry production guide
TRANSCRIPT
LOWTUNNELSTRAWBERRYPRODUCTIONGUIDE
By:
KaitlynOrde&BeckySidemanUniversityofNewHampshire
MarvinPritts
CornellUniversity
KathleenDemchakPennStateUniversity
Published:June2018Acknowledgements:WethankDr.KimLewersoftheUSDA-ARSinBeltsville,Marylandforherthoughtfulreviewandmanycontributionstothisguide.WearealsogratefultoDavidPike,acommercialgrowerinFarmington,Maine,forgenerouslysharingtipsabouthisproductionsystemandlowtunnelmanagementwithus.FundingprovidedbytheNationalInstituteofFoodandAgriculture,U.S.DepartmentofAgriculture,SpecialtyCropsResearchInitiativeunderAwardNumber2014-51181-22380(TunnelBerries),theNewHampshireAgriculturalExperimentStationHatchProject#NH00635,theNewHampshireVegetable&BerryGrowers’Association,andUNHCooperativeExtension.Citation:Orde,K.,B.Sideman,M.Pritts,andK.Demchak.2018.LowTunnelStrawberryProductionGuide.UniversityofNewHampshireCooperativeExtensionPublication. https://extension.unh.edu/resources/files/Resource007429_Rep10703.pdf Referencetoanyspecificcommercialproductsormanufacturersdoesnotimplyendorsementorrecommendation.
TABLEOFCONTENTS
I.INTRODUCTIONBenefitsofLowTunnels..........................................................................................................4ManagementRequirements....................................................................................................7StandardLowTunnelComponents..........................................................................................7II.LOWTUNNELSYSTEMEXAMPLES1:Hoops&Twine....................................................................................................................82:DoubleHoops.....................................................................................................................93:CommercialLowTunnelSystems.........................................................................................9III.PLASTICSELECTIONPlasticThickness....................................................................................................................10LightModification..................................................................................................................11EffectsofLowTunnel&MulchColoronTemperature............................................................11IV.PLASTICMANAGEMENT1:OverheadCover.................................................................................................................122:OneSideLowered..............................................................................................................133:Ridge.................................................................................................................................13V.TIPSFORSUCCESSHoops....................................................................................................................................14AnchorObject..............................................................................................................................14PlasticCovers...............................................................................................................................15SecuringPlastic.............................................................................................................................15Ventilation....................................................................................................................................16GroundingStakes.........................................................................................................................18VI.WINTERPROTECTION.......................................................................................................18
VII.DAY-NEUTRALSTRAWBERRIES........................................................................................19
VIII.ECONOMICS..................................................................................................................20
IX.ADDITIONALRESOURCES..................................................................................................22
X.REFERENCES......................................................................................................................24
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I.INTRODUCTIONThis guide is intended to provide an introduction to low tunnel systems and to shareconstructionandmanagementtipsforlowtunnelstrawberryproduction.Informationpertainsto theuseof lowtunnelsduringspring,summer,and fallmonths.Thereareother importantconsiderations for low tunnels installed for winter protection in cold regions with snowfalllikely; seeUsingLowTunnels forOverwinteringCrops:LessonsLearnedformore informationonthistopic.
BenefitsofLowTunnelsPlasticcovered lowtunnelsarewell-suitedtoprotect fruitduringthe long growing season of day-neutral strawberry varieties, butmay also be useful in protecting the short and valuable June-bearing (short-day) crop. Research conducted in Minnesota,Maryland, and theNortheast shows that low tunnels can have anumberofpositiveeffectsonstrawberryproduction,including:
1. ProtectingfruitmarketabilityLowtunnelsactasabarrierbetweenplantsandtheenvironment,protectingfruitfromdamagecausedbyprecipitation.Thestructuresalsoofferprotectionfrominclementweather,includinghailandstrongwinds(Fig.1),andhavebeenreportedtoreducesunburnonfruit.
2. ReduceddiseaseincidenceMany plant diseases, including anthracnose fruit rot (Colletotrichum acutatum) andBotrytis (Botrytis cinerea) rely on high relative humidity for sporulation and rain forsporedissemination.Byeliminatingstandingwater, sporulation (especiallyofBotrytis)anddiseasepressurecanbereduced.
3. GreatertotalyieldsandlargerfruitsizeIn some years and locations, day-neutral strawberry plants grown under low tunnelshaveproducedgreatertotalmarketableyieldsthanplantsgrownonopenbeds(Lewersetal.,2017;Petranetal.,2016;VanSterthemetal.,2017).Lateseasonyieldsduringthemonths of October and November also tend to be increased under low tunnels,especiallyasgrowingconditionsdeteriorate.
Fig. 1: Hail experienced insouthern NH, June 2017.Photo:A.Orde
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4. Ahigherpercentofmarketablefruit
Even when marketable yields are not greater under low tunnels, plants consistentlyproduceahigherpercentageofmarketableyieldthanplantsgrownonopenbeds(Fig.2andFig.3).ExperimentsconductedinattheUniversityofNewHampshireandCornellUniversity have found the percentage of marketable yield is an average of 10-15%greater under low tunnels than open beds. Following rain, there is even a greaterdifferencebetweenlowtunnelsandopenbeds.Forexample,followingrainononedateinOctober2017,approx.50-70%ofyieldwasmarketableunderlowtunnels,whilelessthan3%weremarketablefromopenbeds(Pritts,2017;Ordeetal.,2017).
5. Extendedfruitproduction
When low tunnel sides are closed, daytime maximum air and soil temperatures aregreater within low tunnels than open beds (Fig. 4), this may promote growth (andflowering)duringtheearlyspringandlatefallmonths.ResearchfromtheUniversityofNewHampshire reports that in 2017, yield from the day-neutral variety ‘Albion’ wasgreater under low tunnels than open beds during four of the last five weeks of theseason (Fig. 5). During late-season production, even though nighttime air and soiltemperaturestendtobecomparabletoopenbeds(therearesomeexceptions), ithasalsobeenreportedthatlowtunnelsmayprovidesomedegreeoffrostprotection.
6. Reducedrunneremergence
Very preliminary findings suggest that low tunnelsmay reduce runner emergence forsome day-neutral varieties. In a one-year experiment conducted in 2017 in NewHampshire,theday-neutralvarieties‘Aromas’,‘Monterey’and‘SanAndreas’producedsignificantlyfewerrunnersperplantunderlowtunnelsthanonopenbeds(whengrownonblackplasticmulch).ThisexperimentisbeingreplicatedforasecondyearatUNHin2018.Itdoesnotappearthatallvarietiesproducefewerrunnersunderlowtunnels,butinaplasticulturesystemwhere runnerproduction isnotdesired (andremoval is timeconsuming and costly), this response may be an additional benefit to growing somevarietiesunderlowtunnels.
Fig. 2 and Fig. 3: Fruit following rain in August 2016 (left) and in November 2017(right). Inbothpictures, the containeron the left contains fruit fromopenbeds (nolowtunnel)andthecontaineronrightcontainsfruitfromlowtunnels.Photos:K.Orde
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Fig. 5: Marketable yield (lbs/acre) of the day-neutral variety ‘Albion’ in Durham, NHduringthelastfiveweeksofthe2017season.Plantsunderlowtunnelsproducedhighermarketable yields in all weeks exceptOct. 15-21 (P ≤ 0.05). Error bars are ± one SE.
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AirTemperature:April17- 24,2018 LowTunnelAirOpenBedAir
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Temperature(F)
SoilTemperature:April17- 24,2018 LowTunnelSoilOpenBedSoil
Fig.4:Dailyfluctuationsinair(topgraph)andsoil(bottomgraph)temperaturesforaone-weekperiodinApril2018.Solidlinesareopenbeds(nolowtunnel)anddottedlinesareforlowtunnels.
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HowMuchManagementTimeisRequired?Low tunnel systems are relatively easy to install but do require some degree of activemanagement throughout the growing season. Wind and rain can trigger the need foradjustments to the system and it is important to check on tunnels to ensure plastic coversremaintautandwellventilatedduringsummermonths. StandardLowTunnelComponentsRegardless of the low tunnel system (commercial or homemade), there are four standardcomponents:
1. Hoops: Hoops are inserted into the groundwith one leg on each side of the bed tocreateatunnelframeapproximately2-3’aboveplants.Hoopsareoftenmadeofsteel,butcanalsobecreatedwithconduitorPVCpiping.
2. Plastic:Agriculturalplasticisusedtocoverthehoopstopreventwaterfromcomingindirectcontactwithplantsandfruit.Therearemanyoptionsforlowtunnelsplastics,andfilmsareavailableinarangeofthicknessesandlighttransmissionproperties.Perforatedplastics,whichencouragesairflowwithintunnels,arealsoavailable.
3. Tie-downmaterial:Twine,parachutecord,orbungeeelastics isusedtosecureplastictothelowtunnelframe.
4. Anchorobject:Astake,post,orpipeisusedatbothendsofthetunnelasagrounding
objectfortheplasticcover.
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II.LOWTUNNELSYSTEMEXAMPLESThe following examples of in-ground low tunnels are presented to show the diversity ofmaterialsandapproachesthatcanbetaken,butareonlyasample,asitispossibletotailorasystem to your budget and needs. Commercial growers have developed completely above-ground lowtunnel systems thatdonotaffix to theground,allowing the tunnel tobemovedoverdifferentsectionsofthefieldasneeded,thoughsuchsystemswillnotbeoutlinedinthisguide.1:Hoops&TwineThismethodutilizeshoopsandtwine (oranother tie-downmaterial) thatusuallycrisscrossesbetweenhoopstoholdplastictotheframe(asonahoophouse)(Fig.6–Fig.7).Itisnecessarytoincludeanobjectoneachhoopthatthetwinecancatch.Forwirehoops,arubberstoppercan be inserted onto the end of the hoop (Fig. 8) but for PVC or conduit hoops, it may benecessary to install a hookonto thehoopor in the groundat thebaseof thehoop.Rubberstoppers canbe liftedhigherupon thehoop to keepplastic ventilated, butdoingwillmakelowering sides more labor intensive and require adjustments to the twine be made.Modifications to theHoops& Twine system include using separate pieces of twine for eachhoop instead of a long piece that crisscrosses between hoops. [A detailed material list andinstallationinstructionsforthissystem(showninFig.6)areprovidedbyDr.KimLewersoftheUSDA-ARSinBeltsville,MDonpage24.]
Fig.8:Rubberstopperusedfor
attaching twine to hoops. Thestopper is installed parallel tothe ground and has a holedrilled through the middle.Photo:K.Lewers
Fig.6:Twinetiedateachhoopwithknotforlatertighteningvisible.Photo:K.Lewers
Fig.7:TwineinstalledinacrisscrossfashionbetweenhoopsinLablachère,France.Photo:http://vivacoop.pagesperso-orange.fr/fraises.html
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2:DoubleHoopsThedoublehoopsystemusesnotwine.Instead,afterplasticisinstalledontopofafirstsetofhoops,asecondsetofhoopsisplacedovertheplastic(Fig.9).HoopsareoftenmadeofPVCpipingbutothermaterialsmaywork. It is importanttoensurehoopsprovideenoughtensiononplastictoensuretunnelssidesdonotfallandplasticremainsventilated.Itmaybepossibletouseanarrowpieceofplastic,butchallengestothissystemhavebeenreported;specifically,ensuring plastic is held in place and does not slide off tunnels,which has been cited as theprimaryissue.
3:CommercialLowTunnelSystemsThe advantage to using a kit is that the system is ready to install andmaterials have beendesigned specifically for low tunneluse.Componentsoften contain characteristics thatmakemanagementeasier,suchasplasticcoveredhoopsfortheendsofrows(Fig.10),“pegs”atthebaseofhoopsforattachingthetie-downmaterial(Fig.11),andgroundingstakestokeephoopsin the ground (Fig. 12). Currently there are only a limited number of commercial low tunnelsystemsavailable,butindividualcomponentscanbepurchasedfromseveralcompanies.
Fig. 9: Double hoop system used for strawberry production in the Republic of Cyprus.Photo:PolyAgCorp.
Fig. 10: Plastic covered start/end hoop (left); Fig. 11: Low tunnel hoop with peg (middle); Fig. 12:Groundingstakesforindividualhoops(right).AllarecomponentsoftheDuboissystem.Photos:K.Orde
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III.PLASTICSELECTIONPlasticThicknessTherearemanyoptionsinlowtunnelcoversforstrawberryproductionsystems.Forstrategiesforplasticmanagement,pleaserefertothePlasticManagementsection(page11).
ThinPlastics(1-2mil)Thin, lightweightplasticsarepleasant tohandleduring installationandcanbe raisedandloweredwithease.Suchplasticsarealsoavailableinasuitablewidthformost lowtunnelsystems (~8’ wide), eliminating the need to cut plastic to the appropriate size prior toinstallation.Thinplastics canalsobeacquiredwithperforated sides toencourageairflowwhen sides are lowered. Depending on the hoops and how high plastic is raised on thehoops,thinplasticwilloften lowertothegroundduringrainorstrongwind.Whilethis iscertainlyanadvantagewhen itcomestoprotecting fruitquality, laborwillberequiredtoraise sides again once the storm passes to ensure high temperatures do not negativelyaffectfruitset.Disadvantagestothinplasticsincludeahigherlikelihoodofdevelopingholesorstretching.Thisisespeciallytrueifplasticisnotinstalledtautlyorsidesareraisedtoohighandwateraccumulates on the top of the tunnel. Commercial growers report replacing thin plasticsannually.Partially-perforated1.5milplastichasbeenusedfortwogrowingseasonsattheUniversityofNewHampshire,butthesideswerenoticeablylesstautinthesecondyearofuse.Lowtunnelscoveredby1.5milfilmareshowninFig.13.
Fig.14:Fullyventilated6milplasticcoveredlow tunnels. Sides have been rolled underanduptokeepsidesraised.Photo:K.Orde
Fig.13: Low tunnels coveredwith1.5milplasticwithperforated sides only. Perforation can be seen wheretheplasticmeetssoil.Photo:K.Orde
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ThickPlastics(4-6mil)Basedonourexperience,thickplasticstendtobesturdierand less likelytoriporstretchthanthinplastics,andcandefinitelybeusedformultipleyears.However,theyalsotendtobemorechallenging tohandleand time-consuming to install,and it isoftennecessary tocut theplastic to theappropriatewidth for low tunnels (although it ispossible to specialordernarrowrolls).University of New Hampshire researchers found that when 6 mil plastics were used inconjunctionwiththeDuboislowtunnelhoopsandbungeeelastics,sideswouldnotremainraisedbysimplyliftingor“scrunching”thesidesup.Instead,researchersneededtorolltheplasticinwardandupinsegments(Fig.14).Thismethodwasveryeffectiveinensuringgoodairflowanditkeptplasticinplaceallseasonbutmadeloweringplasticforeachraineventtoo labor intensive. Therefore, if using thismethod, it is likely that plastic would be leftventilatedandonlyprovideoverheadprotectionuntil latefallor intheeventofaseriousstorm. Note: separate bungee elastics were attached at each hoop in this experiment.Crisscrossingthetie-downmaterialbetweenhoopsmayhelpalleviatethisproblem.
LightModificationTransparent(or“clear”)agriculturalplasticstransmitahighpercentageofbothultra-violet(UV)and infrared (IR) solar radiation. UV light (especially UV-B) can be helpful in inhibiting somepathogens(suchaspowderymildew),butforBotrytiscinerea,blockingUVradiationcanreducefungal sporulation. Additionally, because some insect pests cannot navigate in environmentslacking UV light, reduced pest damage has been reported for UV-absent environments(Papaioannouetal.,2012).Ontheotherendofthevisiblespectrum,IRwavelengthsareheatgenerating. Closed protective structures covered by plastics that block or reduce thetransmission of IR wavelengths tends to have a lower daily maximum air temperature thantunnelscoveredbytransparentplasticsthatallowahighpercentageofIRlighttransmission.
EffectsofLowTunnel&MulchColoronTemperature AstudyattheUniversityofNewHampshiremonitoredairandsoil temperaturesunder lowtunnelscoveredwithboth6milUV-blockingandIR-limiting,6milUVandIR-transparent,and1.5mil transparentcommercialplastics.Researchersreportthatduringthesummermonthswhen the sidesof low tunnelsare raised (ventilated), air temperaturesare the sameunderlow tunnels as open beds. However, once low tunnel sides are closed in the fall, dailymaximum air temperatures are increased within closed tunnels. The highest temperaturesrecorded were under transparent films, which were often 40°F warmer than open beds.MaximumtemperaturesunderanIR-limitingplastic(6mil)wascoolerthantransparentfilms(especiallywhencoveringwhiteplasticmulch)butstillwarmerthanopenbeds.Soiltemperaturesunderwhiteplasticmulchwerecoolerthanblackplasticmulchduringboththesummerandfallmonths,regardlessofplasticproperties.Thepresenceoflowtunnelsdid,however,increasedailymaximumsoiltemperaturescomparedwithopenbeds.Nighttimesoiltemperaturesinthefallwereslightly increased(by2-5°F)under6milplasticandfor1.5milplasticcoveringlowtunnelsonblackmulch(butnot1.5milcoveringwhitemulch).
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IV.PLASTICMANAGEMENTIf low tunnel sidesare lowered for rainorwind, it is important theybe raisedonceweatherclears to ensure high temperatures do not negatively affect fruit set. Another importantconsideration ishowwaterwillbeshedofftunnels. Ifplastic israisedtoohighonthehoops,rainwatermaypoolandstretchplasticorcompromisethetunnelstructure.Thefollowingareexamplesofplasticmanagement strategiesusedby growers and researchers throughout theregion.SeeVentilation(page16)fortipsonpreventingwateraccumulation.1:OverheadCoverThismethodprovidesoverheadprotectiontoplantsatalltimes.Ifusingthickplastic,sidescanremainraisedduringrainevents,thoughthiswillonlyprovidemoderateprotectiontofruit(Fig.15).Iftheoverheadcovertechniqueiscoupledwiththinplastics,sidescanveryeasilybemanuallyloweredforrain.Infact,thinplasticsoftenlowerontheirownfromtheweightofthewateronthetunnel,necessitatinglabortore-ventilatetunnelsafterthestormhaspassed.Itisimportanttorememberthattokeepraincompletelyoffoffruitandplants,itisnecessarytoclosethelowtunnelsides.Fig.16illustrateshowthinplastictendtodropandthickplastics(withsidesrolledup)stayventilatedduringprecipitation.
Fig.16:Alowtunnelcoveredwiththin1.5milplasticthatautomaticallyclosedduringarainevent(left).Atunnelcoveredwithathick/heavyweight6milplastic(right).Photo:K.Orde
Fig. 15: Thick 6 mil plastics rolledunder and up in segments.Photo:K.Orde
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2:OneSideLoweredUsing this approach, one side of the tunnel is lowered to the ground (often, the side ofprevailingwind)andtheotherisleftraised(Fig.17andFig.18).Thereareseveraladvantagestothisstrategy:ifthelocationiswindy,loweringthesidetowardstheprevailingwindprotectsplantsfromwindwhileensuringgoodairflow.Perhapsthemostsignificantadvantageisthatonlyonesideofthetunnelneedstobeloweredduringasignificantrainevent,reducingtimeandlaborinputformanagement.
3:RidgeWhenusingthismethod,plasticislifteduptotheridgeofthetunnel(Fig.19andFig.20).Thisapproachessentiallyeliminatestheneedtoactivelymanageplasticexceptforduringperiodsofprecipitationwhenbothsidesarelowered.Thismaybeagoodstrategyforproducerswhodonothavetheabilitytocheckonthetunnelsfrequently,butarewillingtodeploylabortolowersidesperiodically.However,sidesmustbequickly loweredwhen itdoesrain inordertoreapthebenefitsofthelowtunnels.
Fig.17(left):Plasticloweredononesidewithoutoverheadcover.Photo:M.PrittsFig.18(right):Plasticloweredononesideaswellasoverheadcover.Photo:M.Pritts
Fig.19andFig.20:Ridgemethodofplasticmanagement.Photos:B.Poling(left)andK.Orde(right)
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V.TIPSFORSUCCESSWe highly recommend constructing at least one complete tunnel before installing individualcomponentsformultipletunnelssothatmodificationstospacing,anchoring,etc.canbemadeasproblemsare identified.Thefollowingaresomekeytipsforthesuccessful installationandmanagementoflowtunnels.Hoops
² Hoopscanbeplacedinthefieldanytimebutarebothersometonavigatewhenplantingbyhandandwouldcompletelypreventmechanical transplanting.Thus,we recommendwaitingtoinstalluntilafterplanting.
² A hoop distance of 5’ is recommended by commercial manufacturers. While this mayseemcloseanditistemptingtoincreasethisdistance,doingsomakesitmorechallengingtokeepplasticinplace.
² Topreventtheterminalhoopfromcollapsinginward,installthelasthoopateachendofthetunnelata60°angle(facingawayfromthetunnel).
AnchorObject
² Anchoringplastictosturdyanchorpostsattheendsofeachrowisacriticalstep intheinstallation process. Commercial growers have reported collapsed tunnels from poorlyinstalled anchors. Hollow steel pipes measuring 1¼” x 24” have worked well at theUniversityofNewHampshire(Fig.21).T-postshavebeenusedsuccessfullyelsewhere,butwoodenstakesshouldbeusedwithcaution,asourexperiencesuggeststheymayrotandbreakbylateseason(Fig.22).
² Install theanchorobjectdeeply intotheground,asthestability ismore importantthanthelengthofstakeaboveground.
² Ifplasticisbeingwrappeddirectlyaroundtheanchorobject,installtheanchorobjectata45°angletopreventplasticfromslidingoff(Fig.21).
Fig.21andFig.22: (Left)Hollowsteelanchorpipe. (Right)Awoodentomatostakeusedastheanchorobject.Whilereadilyavailable,theymaybreakunderthetensionfromthetunnels.Photos:K.Orde
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PlasticCovers
² If plastic ispurchased ina large roll itmayneed tobe cut to the correctwidth for lowtunnels.Theexactmeasurementswilldependonthelowtunnelshoopsbeingused,but8’wideisthestandardwidthofcommerciallyavailablelowtunnelplastics.
² Take caution not to damage thin plastics during the cutting or installation process.Draggingplasticoverrocks,stakes,etc.cancompromisethefilmenoughthatitcan(andwill)splitoncetheplasticisinstalledoverhoopsandthereistensiononit.
² Ifplasticisbeingattacheddirectlytotheanchorobjectattheendsofrows,factorinafewextrafeetofplasticforeachendofthetunnel.
SecuringPlastic
² Onceplastichasbeenlaidoverhoops,itneedstobesecuredtotheanchorpipe.Zipties(>12”)areaquickandeffectivewaytoattachplasticaroundtheanchoringobject,andasmalltensionerorratchetatbothendsofthelowtunnelcanbeusefulforremovingslacklengthwiseintheplastic(Fig.23–Fig.25).Wesuggestleavingseveralfeetoftwine/cordingbetweenthetensioner/ratchetandtheplastic,sothattheslackcanbetakeninthroughouttheseason(Fig.25).
² Possiblythemostimportantstepistightinstallationofthetie-downmaterial(twine,bungeeelastics,etc.)ateachhoop.Thetie-downmaterialremovesslackintheplasticandkeepsittaut,preventingwaterfromaccumulatingontopofthetunnels.Tightinstallationwillalsopreventplasticfrombeingblownoffthehoops.Agoodruleofthumbisthateachhoopshouldlooklikeasmall“wave”(Fig.26).[Note:avoidsisalwhichmayfallapart.]
Fig. 24: Tensioner installed on awoodentomatostake.Photo:K.Orde
Fig.23:Zipties,tensioner,andparachutecordusedforattachingplastic.Photo:K.Orde
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² Itishelpfultohaveaplanfortighteningthetie-downmaterialonceortwicethroughoutthegrowingseason.Bungeeelastics,especially,willstretchandloosenastheseasonprogresses.Methodsfortighteningthetie-downmaterialincludewrappingthebungeearoundtherubberstopper(Fig.8,page8)oraroundthepegatthebottomofthelowtunnel(ifthehoopcontainsapeg).Slackinthelinecanalsobepulledandanewknottied.Parachutecordortwinecanbeuntied,tightened,andretied.
Fig.27:Accumulatedwateron1.5milplastic.Wateraccumulationcanbepreventedbyensuringthebungeeelasticsareverytightandtheplastichasnotbeenliftedtoohighonthetunnelhoops(whereitcannotdropaswateraccumulates).Photo:K.Orde
Fig.25:Anchorpipeattachedto1.5milplasticusingtensionerandparachutecord. Photo:K.Orde
Fig.26:Bungeesinstalledtocreatea“wave”ateachhoop.Photo:K.Orde
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Ventilation
² For thinplastics in their firstyearofuse, lowtunnelssides typically remainventilatedwhenplasticisliftedor“scrunched”up.Ifplasticisusedformorethanoneyear,itmaybecome unevenly stretched and need to be lifted higher on the hoop to keep itventilated.
² Theheightinwhichtheplasticisliftedonlowtunnels(especiallystraight-sidedhoops)willaffectthetunnelsabilitytoshedwaterduringrainevents.Ifplasticisraisedabovetheeaveofthehoop(Fig.28),watertendstoaccumulateonthetopofthetunnelandcanstretchplastic(Fig.27,previouspage).Alternatively,ifplasticisraisedtojustbelowthe eave (Fig. 28), plastic will mostly lower automatically before too much wateraccumulates,preventingexcessivepoolingwhichmaystretchplastic.
² For thick plastics, rolling plastic under and up in 3-4” segments is a very effectivestrategytokeeptunnelsventilated.However,itisimportanttonotethatitisverylaborintensiveandtimeconsumingtolowersidesoncetheyhavebeenrolled.
² Iftunnelsidestendtoperpetuallyfall,thisisanindicationplasticisnotsecuredtightlyenoughlengthwiseand/orthatthetie-downmaterialisnottightenoughateachhoop.
² Whenlowtunnelsidesare loweredforrainorearly/late inthegrowingseason,waterdoesnotaccumulateontunnels(Fig.29andFig.30).
Fig. 28: Plastic “scrunched” to above (left) and below (right) the eave of the hoop.Photo:K.Orde
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GroundingStakes
² Groundingstakesareintendedtoholdlowtunnelhoopsinplaceduringstrongwindorstorms. Theyareeasy to install (evenplentiful rockshavenotobstructed installation)andwehavefoundthembeveryeffectiveinkeepingtunnelsinplaceduringstorms.
² Ifusing theDuboishoops, it isadvantageous tobeable to slightly liftonesideof thehoopthroughouttheseasonsothetie-downmaterialcanbewrappedaroundthepegatthebaseofhoopstotightenit.Sinceitisverydifficulttolifthoopsoutofthegroundwithout removing thegroundingstake,wesuggest installingonlyonestakeperhoop,alternatingsidessothatbothsidesofthetunnelaresecured.Ifusingahomemadewire,PVC,or conduithoop, rebar (bent intoahook) canbe inserted into thegroundasananchorforthetie-downmaterial.
² Foreasiest removalof grounding stakes, install themperpendicular (straight) into theground,asopposedtoatanangle(Fig.31).
Fig.29andFig.30:1.5milperforatedplastic liftedforharvest(left)andclosedforlateseasonproduction(right).Photo:K.Orde
Fig.31:Groundingstakeinstalled
vertically(left)andatanangle(right)
ontothepegatthebaseofthelow
tunnelhoop.Photo:K.Orde
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VI.WINTERPROTECTIONIntact low tunnels have been overwintered in Maryland and trials are underway at CornellUniversity in New York, but we do not currently have recommendations for overwinteringintact low tunnels in northern New England. Not only is snow load likely to stress tunnelcomponents in the Northeast, but low tunnels alone will not provide protection from coldwintertemperatures.Straworrowcoverneedtobeusedduringthewintertoensurethereisnotsignificantplantloss.If low tunnels are used in a June-bearing production system, we suggest they be fullyassembledpriortobloomanddisassembledattheendofthefruitingperiod.Forday-neutrals,werecommendusinglowtunnelstocarryfruitproductionintothelatefallmonths,butwhenitis time to protect plants for winter, there are several options for preparing low tunnels forwinter.
LowTunnelPlasticLow tunnel plastic can be removed from tunnels or left in the field over the winter.Detachingplasticfromtheanchorpipesisquickandeasy,andstoringthefilminsideduringthewinterensuresitiscleanandundamagedthefollowingspring.Wesuggestcuttingtheziptiesthatconnecttheratchet/tensioner(andplastic)totheanchorobjectattheendsofrows,rollingtheplasticup,andlabelingitwiththerownumberforfastsetupthefollowingspring.Itisalsopossibletoslidethelowtunnelplastictoonesideofthehoopsandleaveitinthefieldoverthewinter.Thishasbeenreportedtobeasuccessfulapproachinsomecases,butresearchersatPennStatehavenotedthatplasticbecomesdirtyandfoggythenextspring,andmayrequirecleaning.Hoops,GroundingStakes,AnchorPipesRegardless of the approach taken with the low tunnel plastic, leaving other tunnelcomponentsinthefieldoverthewintermakesforaquicksetupinthespring(Fig.32–Fig.37). There is added wear and tear associated with leaving materials outside during thewintermonths,but if theplan is to re-construct the low tunnels the followingyear, timeand labor will be saved by having the hoops, ground stakes, and anchor pipes alreadyinstalledandreadytoattachtheplasticto.Additionally,preliminaryresearchsuggestslowtunnelsmaybeusefulforhasteninggrowthandfloweringinthespring(bothforshort-dayandday-neutralplants).MulchingMethodWhenhoopsremaininthefieldduringthewinter,itmaybeeasiertousestrawmulchthanrowcoverforwinterprotection.Rowcoverhasbeenusedwithinhoops,butthiswouldrequireanarrowpieceofrowcoverbeappliedoverplantsandsecuredonbothsidesofthebed,allwithinthetunnelframe.
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Fig.32:December2017-Strawberryplantsmulchedwithstraw.Plasticwasremovedbutotherlowtunnelcomponentsremaininthefield.Photo:K.Orde
Fig.33:December2017–Hoopsarevisiblefollowingfirstsnow.Photo:K.Orde
Fig.34:April3,2018–Day-neutralstrawberryplantsafterstrawmulchwasremovedthefollowingspring.Photo:K.Orde
Fig. 35: April 3, 2018 - Low tunnels re-constructedoverplantsfollowingtheremovalofmulch.Photo:K.Orde
Fig.May28,2018–firstfruitharvestedfromday-neutralplants in the second year of fruit production.Photo:K.Orde
Fig. June1,2018 – ‘Seascape’ fruitunderlowtunnels.Photo:K.Orde
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VII.DAY-NEUTRALSTRAWBERRIESFor years, June-bearing (short-day) strawberry varieties have been the dominant plant-typegrownintheNortheast.June-bearersinitiateflowersundershort-dayconditionsinthelatefallandproducefruitforashort4-6weekperiodthefollowingyear,fromaboutmid-JunetoearlyJuly.Whilethis“strawberryseason”ismetwithenthusiasmbybothconsumersandproducers,theshortfruitingperiodpreventsregionalgrowersfromsatisfying(andprofitingfrom)strongconsumerdemandforlocalstrawberriesbeyondthisperiod.Additionally,poorweatherduringthese few weeks can cause significant damage to the marketability of the crop and bedevastatingforcommercialgrowers.InotherregionsoftheUnitedStatesandthroughouttheworld,day-neutralvarietieshavebeenwidely adopted to fill gaps in production.Unlike June-bearers, day-neutral strawberry plantshave theability toproduce flowers (and fruit) continuously through spring, summer, and fallmonths,mostlyindependentofday-length.Somecommercialgrowersreportedlowyieldsandsmall fruit size from several of the earliest day-neutral varieties released in the 1980’s andunderstandably,mayfeelapprehensivetotryday-neutralsagain.However,anewgenerationofcultivarshasbeenavailablesincethelate2000’sandseveralcultivarsconsistentlyproducehigh annual yields (>15,000 lbs/acre) and a large fruit size in colder climates, including theUpperMidwestandnortheasternregionsoftheUS.Ifplantedearlyspring(late-April)inaplasticulturesystem(raisedbeds,plasticmulch,anddripirrigation), these day-neutral varieties will begin fruiting within 10 weeks and continueproducing fruit into November (Fig. 38 – Fig. 40). Fruit production lasts approximately fourcontinuous months (July-November) in the year of planting, peaking in September in NewHampshire.Plantscanthenbemulchedandover-wintered,andwillfruitagaininthespringofthe second year. Following second year spring production, day-neutral plants are oftendiscarded,butsomegrowersdokeeptheminproductionthroughthesummerandfallmonthsofthesecondyear.Combining day-neutral cultivars with existing June-bearing production can effectively extend thestrawberry production season to a minimum of sixmonths in the Northeast. To achieve high yields andseason long production, runners must be removed bi-weeklyormonthly,andplantsfertilizedweeklythroughthe drip irrigation system, typically at a rate of 5 lbsnitrogenperacre.Varietyperformance,includingwintersurvival rates are currently being investigated at theUniversity of New Hampshire and Cornell University.Varieties appear to differ in yield, productionpatterns,andwinter survival. ‘Albion’ is currently recommendedforitsreliablemoderate-highyieldsandexcellentflavor.
Fig. 38: ‘Aromas’ fruit on October 6,2017inDurham,NH.Photo.K.Orde
22
s
VIII.ECONOMICSTheyield(andfinancial)advantageaffordedbylowtunnelsislikelytodependonanumberoffactors, especially the frequency of precipitation and other storm events, location, and thehealth and productivity of the planting. Depending on these factors, the inclusion of lowtunnels may or may not increase yields, but low tunnels consistently increase the percentmarketableyieldof theplantsbeneath them,preventwaterdamageon fruit, reducediseasepressure,andmaydecreaserunneremergence.Wesuggestlowtunnelsserveasaformofcropinsurance with the capacity to “save” a crop that may otherwise be lost during poor orinclementweather.A complete low tunnel system (steel hopes, plastic, bungee elastics, grounding pipes, etc.)requiresaninitial investmentofapproximately$20,000peracre.Hoopsandgroundingstakescanbere-usedformanyyearsandplasticwillneedtobereplacedperiodically.Grossrevenueatthereportedrateof$2.90/lbwouldrangefrom$43,500/acre(basedon15,000lbs/acre)to$58,000 (based on 20,000 lbs/acre). For direct market sales, revenue could reach $80,000lbs/acre(basedon20,000lbs/acre).Lowtunnelsmaycreateanevenmoresignificantfinancialreturnduringyearswithexceptionalweather events. For example, in 2013 researchers at the University of Minnesota reportedsubstantial yield increasesunder low tunnels followinghail (8,500 lbsperacrehigherunderlowtunnels),whichwouldresultin$27,917additionalrevenueperacreunderlowtunnelsthanopenbeds(basedonthereportedrateof$2.90/lb;USDANASS,2016).Ifyieldsweretodoubleunder low tunnels,as theyhave inPennsylvania, the resultwouldbeanadditional$9,570 inrevenueperacre.Lastly,ifyieldsdidnotincreaseunderlowtunnels(ashasbeenobservedinNewHampshireandMinnesotain2016,adroughtyear), lowtunnelsarestillapttodecreaseunmarketable yield and may decrease runner emergence, reducing labor required for theremoval of fruit and runners. Under all these circumstances, revenue potential for aplasticulture strawberry system is great enough to cover the initial purchase cost of a lowtunnelssystem.
Fig. 40: ‘Albion’ fruit on November 20, 2016 inDurham,NH.Photo:K.Orde
Fig. 39: ‘Albion’ fruit on October 10, 2016 inDurham,NH.Photo:K.Orde
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IX.ADDITIONALRESOURCESExtendingLocalStrawberryProductionUsingDay-neutralCultivarsandLowTunnelTechnologyByMarvinPrittsandLauraMcDermott,CornellCooperativeExtensionhttp://hort.cornell.edu/fruit/pdfs/low-tunnel-strawberries.pdfStrawberryProductionSeasonExtensionUsingLowTunnelsByKimLewers,USDA-ARSBeltsville,MDhttp://www.hort.cornell.edu/expo/proceedings/2013/Berries/BerriesLewersLowTunnels.pdfUSDA-SCRISponsoredTunnelBerrieshttps://www.tunnelberries.org/Season-longStrawberryProductionwithEverbearersByWillyLantz,HarrySwartz,KathleenDemchakandSherryFrickhttp://www.sare.org/Learning-Center/SARE-Project-Products/Northeast-SARE-Project-Products/Season-Long-Strawberry-Production-with-Everbearers-for-Northeastern-ProducersDayneutralStrawberryProductionGuideByMarvinPritts&AdamDalehttps://ecommons.cornell.edu/bitstream/handle/1813/3275/DayneutralStrawberryProductionGuide.pdf;jsessionid=A262BC9C332E0FD21B57FC84707FB903?sequence=2UsingLowTunnelsforOverwinteringCrops:LessonsLearnedByBeckySideman,UniversityofNewHampshirehttps://extension.unh.edu/resources/files/Resource004419_Rep6301.pdf
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Hoops&Twine-MaterialsandInstallationInstructionsCourtesyofKimLewers,USDA-ARSBeltsville,MDMaterials:
• 1/4”stainlesssteelwire,cutinto12’pieces(inMaryland,1/4”haswithstoodtheweightoficeduringinclementweatherbetterthan3/16”)
• Blackpolyethyleneplasticwaterpipe1”indiametercutto6”long.Touseas“stoppers”.Each6”stopperneedsa7/32”holedrilledthroughthecenterofthestopper(perpendicular;seePhoto4)
• Polypropylenebalingtwine(avoidsisaltwine,itmayfallapart)• T-post/anchorstakefortunnelends• Plasticforcoveringtunnels.Upto12’widewillworkforhoopsthissize
Construction:
• Astopperispushedontothe12’pieceofwire,2’fromtheendofbothsides.Thiswillbecomethelowtunnelhoop.
• Hoopsareinstalledinthegroundevery4-5’deepenoughsothestopperrestsjustabovetheground.Thereisnoneedtopre-bendthewire.
• Onepieceoftwineisrundowntheentirelengthofthetunnelbeforeplasticcoveringisinstalled,windingaroundtheridgeofeachhoop.Thisactsasapurlin/ridgepole.
• Next,individual20’piecesofbailingtwinearecutandattachedtoeachlowtunnelhoop.Loopsof20’twinearehookedunderonestopper,liftedoverthelongpieceoftwineactingasthepurlin,andhookedunderthestopperontheoppositesideofthetunnel(seePhoto3).Besuretotietwineinawaythatallowsforlatertightening.
• Layplasticcoveronthegroundthelengthoftunnel.AttachplastictotheT-postsatbothends.
• Next,simplyunhookthetwinefromunderthestopperonthatsideofthetunnel,liftoverthesheet,andre-hookittothestopperunderthesheet.Thissteplooselyattachestheplastictothehoop,preventingitfromblowingaroundwhileitisbeingliftedovertunnels,andessentiallyallowsonepersontosetupthetunnel.
• Theplasticcannowbepulledupontothetunnel,onehoopatatime.• Onceplasticiscoveringtunnels,twineshouldbetightenedjusttothepoint
wherethereisnoexcess.Next,stopperscanbetwisted180°andtwineloopedundereachsideofthestopper.Repeatthissteponbothsidesofthetunnel.
• Givingthetwineahardpulltosnuguptheloops,andasecondknot.• Lastly,tieeachlooptoitsneighboratthetopofthetunnel.Thisstepkeepsthe
“hoopintheloop.”
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X.REFERENCESAnderson,H.2017.EffectsofLowTunnelPlasticTypeonOrganicProductionofDay-neutralStrawberriesintheUpperMidwest.HortScience52(9):S442.(Abstr).Lewers,K.2015.Low-tunnelproductionofstrawberry:learningmoreeveryyear.VirginiaCooperativeExtension/VirginiaTech“VirginiaBeachStrawberryFieldWalk,NewGrowersWorkshopandStrawberrySchoolandTradeShow.”VirginiaBeach,VA.Powerpoint.Lewers,K.S.,D.H.Fleisher,andC.S.T.Daughtry.2017.LowTunnelsasaStrawberryBreedingToolandSeason-ExtendingProductionSystem.Int.J.FruitSci.:1–26
Orde,K.M.,R.GrubeSideman,K.Demchak,R.P.Marini,M.Cooper.2017.EffectsofLowTunnelsonDay-NeutralStrawberryProductionintheNortheasternU.S.HortScience52(9):S267.(Abstr.)
Papaioannou,C.,N.Katsoulas,P.Maletsika,A.Siomos,andC.Kittas.2012.EffectsofaUV-absorbinggreenhousecoveringfilmontomatoyieldandquality.SpanishJ.Agric.Res.10(4):959–966.
Petran,A.,E.Hoover,L.Hayes,andS.Poppe.2016.Yieldandqualitycharacteristicsofday-neutralstrawberryintheUnitedStatesUpperMidwestusingorganicpractices.Biol.Agric.Hortic.8765(July):1-16.Pritts,M.2017.Protectedcultureforberries,lowandhightunnelresearch.NewJerseyAgr.conventionandtradeshow.Accessed8March2018.https://www.youtube.com/watch?v=5ErlnTZNuxMUSDANationalAgriculturalStatisticsService.2017.NewEnglandVegetableandStrawberryReport,2016Crop.VanSterthem,A.,Desjardins,Y.,Gauthier,L.,Medina,Y.andGosselin,A.2017.Useoflowtunnelstoimprovetheproductivityofday-neutralstrawberryplantsundertheQuébecclimaticconditions.ActaHort.1156:555-562.