AGR-153

Harvesting Harvesting practices are similar for dark air-cured anddarkfire-curedtobacco(seeKentuckyCooperativeExtensionpublication AGR-152, Harvesting, Curing, and Preparing Dark Fire‑Cured Tobacco for Market forinformationondarkfire-curedtobacco). Darkair-curedtobaccoisreadyforharvestwhenleavesarematurebutnotoverripe.Formostvarieties,thisistypicallybetweenfiveandsevenweeksaftertopping.Matureleaveswillbethickwithaleatherytextureandasomewhatoilysheen.Theymayshowfaintyellowingor“ripe”spotsandwillcrackreadilywhenfoldedintheheatoftheday. Tobacco harvested immature or “green” will be thin anddifficult to cure, and both yield and quality will be reducedcomparedtomaturetobacco.Overripetobaccoisbrittleanddifficulttohandleandismorepronetoyieldandqualitylossesduetoleafbreakage. Leafbreakagecanbeminimizedifcuttingdoesnotbeginuntil after all dew has evaporated from the leaves. Large,heavy-bodied tobacco should be cut and allowed to wilt tofacilitatehandlingbeforeplacingplantsonsticks (“spiking”).Theamountoftimebetweencuttingandspikingdependsonweatherconditions. Caremustbetakentoavoidsunburn,whichwillresultinacrudegreencolorbeingsetinthecuredleaf(Figures1and2).Underclear,hotconditions,tobaccowillwiltquicklyandmayneedtobespikedwithin30minutestoanhouraftercutting

Harvesting, Curing, and Preparing Dark Air‑Cured Tobacco for Market

Andy Bailey, Department of Plant and Soil Sciences

topreventsunburn.Undercool, overcast conditions,tobaccomayrequirethreeto four hours to wilt withlittle chance of sunburn.Tobaccothatisfieldwiltedinpilesshouldbewatchedclosely to prevent heat-ing and scalding. Cuttingtobaccolateintheafternoonandallowingittolieovernightbeforespikingcanalsoworkwell,providedraindoesnotoccurduringthenighttosplashmudontoleaves. Unlesstobaccoisunusuallysmall,donotplacemorethanfivetosixplantsoneachstickinordertomakehandlingeasierandpromoteairflowthroughthetobaccofollowinghousing.After spiking, tobacco can be allowed to wilt further in thefieldbeforeloading.Placingstickssothatthebuttspointintotheafternoonsunwillminimizethepotentialforsunburnonexposedleaves. Tobaccoloadedonscaffoldwagonsshouldbeplacedintheshadeorcoveredwithaloosefabricmaterialorshadeclothtopreventsunburnpriortohousing.Tobaccoloadedonscaffoldwagonscanbeleftforaslongas48hoursforadditionalwiltingbeforehousing.Tobaccoloadedonflatbedwagonsshouldbehousedassoonaspossibletopreventheataccumulationinthetobacco.

Figure 1. Sunburn in the field. Figure 2. Sunburn effect on cured leaf.

This is a joint publication of the Cooperative Extension Services of the University of Kentucky and the University of Tennessee.

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Housing Sweatingandhouseburnasaresultofovercrowdingtobaccointhebarnaretwoofthemostcommoncuringproblemsindark air-cured tobacco. Sweating and house burn can causesubstantial reductions in cured leaf quality and weight andare also associated with poor leaf chemistry. As yields haveincreasedinrecentyears,growersshouldbeawarethatlargertobaccorequiresmorespaceinthebarntocureproperly,andolderbarnsmaynotaccommodatethesamenumberofsticksastheyoncedidwhenyieldswerelower. Allowing tobacco to wilt as much as possible will makehousingeasierandallowformoreefficientuseofbarnspace.Inadditiontobeingeasiertohandle,fullywiltedtobaccowillbelesslikelytohouseburn,sweat,andmoldandwillyellowandcurebetter. Plantsshouldbespacedevenlyonstickswhilehousingtopromoteairmovementthroughthetobacco.Dependingonthedegreeofwilt,sticksshouldbespaced8inchesapartinnewerbarnswithwidertierspacingwheretobaccodoesnotnormallyoverlapbetweentiers.Inolderbarnswithnarrowertierspac-ing, sticks should be placed 12 inches apart without overlapbetweentiers.Toavoidcuringproblemswithlargertobacco,especiallyinolderbarns,sticksmaybehungoneveryothertier.Ifhangingtobaccooneverytier,theplacementofsticksshouldberegulatedwhenhousingsothattobaccofromanuppertierdoesnotliedirectlyontobaccofromalowertier. Outdoorcuringstructuresusedbysomeburleygrowersarenotcurrentlyrecommendedfordarkair-curedtobaccoduetoincreasedpotentialforweatherdamage.

Curing Curingisastructuredprocessthatrequirestimeandman-agement.Darkair-curedtobaccoiscuredessentiallythesameasburley,butbecauseoftheheavierbodyofdarktobacco,itismorepronetosweat,houseburn,andmold.Underwarmconditions(meandaytimetemperatures>80°Fandmeannight-timetemperatures>60°F),barndoorsandventilatorsshouldbeopenduringtheearlystagesofcuringtopromoteairflowthroughthetobacco.Ifwarm,moistweatherconditionsprevailafterhousing,itmaybenecessarytousesometypeofheattoaidthecuringprocess.Heatmayalsobenecessaryfollowinglateharvestsifcool(meandaytimetemperatures<65°F),dryconditionspersistafterhousing.Heatsourcesthatcanbeusedincludegasburners,cokestoves,orevenwoodfiresusingdrysycamore wood. For dark air-cured tobacco, it is extremelyimportantthat theseheatsourcesbevirtuallysmoke-freesoasnottoleaveany,orverylittle,smokeresidueonleaves.Barntemperaturesduringheatingshouldbekeptlow(notexceeding90°F),astoomuchheatcancauseexcessivedryingorbluing. Moldgrowthinlatercuringstagesisacommonproblemindarkair-curedtobaccoandisduetoexcessivemoistureinthecuring barn (Figures 3a and b). High nitrogen rates can alsocontribute to slow stem drying and potential mold growth.Coveringthebarnfloorwithplasticorevenstrawcanaidinreducingmoisturelevelsinthebarn.Barnventilatorsshouldbeopenedduringconditionsoflowhumidityandcloseddur-ingconditionsofhighhumiditytohelpdriveoffmoisture.Theuseoflowheatwillalsoaidinreducingmoisturelevelsinthetobacco.

Figure 3a. Mold growth on leaf lamina.

Figure 3b. Mold growth on leaf midrib.

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Undernocircumstancesshouldcompoundssuchasalcoholorbleachbeusedtoremovemoldontobacco.Wheremoldgrowthissevere,itmaybenecessarytotakedownsometobaccoontoscaffoldwagonstopromoteadditionalairflow.Forcedairventilationisalsoveryusefulinmanaginghumidityandreduc-ingmoisturelevelsinthebarn. Barn ventilators should be managed to control curingthroughouttheentirecuringprocess.Leavingbarnsopenfortwoweeksandthenclosingthemuntil strippingtime isnotthetypeofmanagementthatwillproducethehighestqualitytobacco.

Preparation for Delivery Thecuringprocessiscompletewhenleafmidribsaredrawndownandfirmallthewaytothestalk(Figure4).Tobaccoshouldbetakendownontoscaffoldwagonsorbulkedassoonaspossibleaftercuring.However,tobaccothatisintoohighordershouldremainhanginginthebarnuntilmoisturelevelsarereduced.Darkair-curedtobaccowilltakeonmoisturemuchmorereadilythandarkfire-curedtobaccoandwillusuallycomeinordernaturally(i.e.,haveenoughmoisturetobesomewhatpliable)withouttheuseofwater.Iftobaccoistakendownandbulkedwhilestalksarestillgreen,itwillonlykeepforashortperiodoftimeandshouldbestrippedassoonaspossible. Ifthereisnogreenremaininginstalksandtobaccoisproperlybulked,qualitycanimproveandtobaccowillremaininordersothatitcanbestrippedatanytime.Bulkedtobaccoshouldbeplacedoffthefloorwithtipsslightlylappinginthemiddleofthebulk.Avoidbulkingtobaccoinhighorderasitwillbemorelikelyto“heat”andspoil. Onlybreathablefabricshouldbeusedtocoverbulkedto-baccosincecoveringwithplasticcancausecondensationthatwillstainthetobacco. Care should be taken in stripping and handling the cropfollowing takedown. Tobacco should be stripped into threedistinctstalkpositions(lug,second,andleaf ),andanygreentobaccoshouldbekeptseparate.Lugscanbefurtherclassed

Figure 4. Dark air‑cured tobacco (upper) ready for takedown.

intogoodlugsandtrashlugsbasedondirtandgroundinjury.Aseparategradeshouldalsobemadeifthereisexcessivemudordirtontheleaforseconds.Anymudcakedonthetailsofleavesshouldberemovedduringstripping.Eachstalkpositionandgradeshouldremainsegregatedthroughdelivery. Careshouldalsobetakenbeforeandafterstrippingtoensurethattobaccoisnotplacednearcontaminantssuchaspesticidesorotherchemicals.Tobaccoshouldremaincleanandfreeoftrash and other non-tobacco-related material during marketpreparation. Betweenstrippinganddelivery,tobaccoshouldbestoredinaclean,dry,andwell-ventilatedlocationwhereitwillbeprotectedfromcontaminationorotherdamage.Onlytobaccofromthecurrentcropyearshouldbedelivered,andtobaccoshouldbeprotectedfromweatherdamageduringhaulinganddelivery.

Educational programs of Kentucky Cooperative Extension serve all people regardless of race, color, age, sex, religion, disability, or national origin. Issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture, M. Scott Smith, Director of Cooperative Extension Service, University of Kentucky College of Agriculture, Lexington, and Ken‑tucky State University, Frankfort. Copyright © 2006 for materials developed by University of Kentucky Cooperative Extension. This publication may be reproduced in portions or its entirety for educational or nonprofit purposes only. Permitted users shall give credit to the author(s) and include this copyright notice. Publications are also available on the World Wide Web at www.ca.uky.edu. Revised 4‑2006.