Sweet Potato r o G Technical Manual -...

Sweet Potato Technical Manual

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CTA

| SweetPotatoTechnicalManual

Sweet Potato Technical Manual

Caribbean Agricultural Research and Development Institute (CARDI)

April 2010

CARDI Root and Tuber Commodity Group

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TheCaribbeanAgricultural Research andDevelopment Institute (CARDI)was founded in 1975asanautonomousinstitutionof12membercountriesoftheCaribbeanCommunity(CARICOM).Themembercountriesare:AntiguaandBarbuda,Barbados,Belize,Dominica,Grenada,Guyana,Jamaica,Montserrat,St.KittsandNevis,St.Lucia,St.VincentandtheGrenadines,TrinidadandTobago.TheInstituteisgovernedbyaGoverningBodycomprisedoftheMinistersresponsibleforagricultureandaBoardofDirectorscomprisedofRepresentativesnominatedbymembergovern-mentsandkeycollaboratingagencies.

CARDIP.O.Bag212,FrederickHardyBuildingUniversityoftheWestIndiesStAugustineCampus,St.AugustineTrinidadandTobago,W.I.

ThepublicationofthisdocumentwasmadepossiblethroughthekindcourtesyoftheTechnicalCentreforAgriculturalandRuralCooperation(CTA).

CTAwasestablished in1983under theLoméConventionbetween theAfrican,CaribbeanandPacific(ACP)GroupofStatesandtheEuropenUnion(EU)MemberStates.Since2000ithasoper-atedwithintheframeworkoftheACP-EUCotonouAgreement.

CTA,Postbus380,6700AJWageningen,TheNetherlands

ContributingAuthors:CARDIRootandTuberCommodityGroupMsPathleenTitus,Agronomist/RootandTuberCommodityProgrammeLeader(Editor)DrJanetLawrence,Entomologist(Editor)MrHermanAdams,PlantBreederDrArdonIton,MarketingSpecialistMrRonniePilgrim,Post-HarvestSpecialistDrGregoryRobin,Agronomist

OtherTechnicalPersonnel:MrBradburyBrowne,TechnicalAssistant

Photographs:JimCaster(UniversityofFlorida),DMichaelJackson(UnitedStatesDepartmentofAgriculture–USDA,SouthCarolinaUSA),LisaMyers(MinistryofAgriculture&Fisheries,Jamaica),CARDIPer-sonnel,AVRDCInternationalCooperatorsfactsheet.http://www.avrdc.org/lc/sweetpot/WestIn-dianweevil.html

©TheCaribbeanAgriculturalResearchandDevelopmentInstitute2010

ISBN:978-976-617-015-8

PSC#HQ/004/10

CARDIRootandTuberCommodityGroup |

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Table of Contents

Page

Acronyms. . . . . . . . . . . . . . . . . . . . iv

Conversiontable .................v

Listoffigures . . . . . . . . . . . . . . . . . .vi

Listofplates . . . . . . . . . . . . . . . . . . vi

Listoftables . . . . . . . . . . . . . . . . . .vii

Preface .....................1

Introduction . . . . . . . . . . . . . . . . . . 2

1Thesweetpotatocrop. . . . . . . . . . . . . 3

2Marketingandsupplyresponse. . . . . . . . .5

3Germplasmselection. . . . . . . . . . . . . 10

4Production. . . . . . . . . . . . . . . . . 16

5Postproduction . . . . . . . . . . . . . . . 33

6Sweetpotatonutrition,usesandvalueaddition . 37

7Disastermitigationandadaptation. . . . . . . 40

8Recordkeeping . . . . . . . . . . . . . . . 42

Bibliography . . . . . . . . . . . . . . . . . 44


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Acronyms

ac acreACP African,Caribbeanand PacificGroupofStatesACP-EU African,Caribbean Pacific–EuropeanUnionAVRDC AsianVegetableResearch andDevelopmentCenterBADMC BarbadosAgricultural Developmentand MarketingCorporationCARDI CaribbeanAgricultural ResearchandDevelopment InstituteCARICOM CaribbeanCommunityCIP InternationalPotatoCentercm centimetersCMV CucumberMosaicVirusCTA TechnicalCentreforAgricul- turalandRuralCooperationDAP DaysAfterPlantingEC$ EasternCaribbeanDollarsEU EuropeanUnionEurepGAP EurepGoodAgricultural Practicesfl.oz fluidounceft footorfeetft² squarefeetg gram(s)gal gallonha hectare

IITA InternationalInstitutefor TropicalAgriculturein inch(es)IPM IntegratedPest Managementkg kilogram(s)KONARC NationalResearch CouncilforKyushuand Okinawalb pound(s)l litre(s)m metre(s)m² squaremetre(s),metre(s) squaredmm millimeterNPK Nitrogen,Phosphorus andPotassiumoC degreesCelsiusoF degreesFahrenheitoz ounce(s)pH Measureofacidityand alkalinityPPM PartsPerMillionSPCFV SweetPotatoChlorotic FleckVirusSPCSV SweetPotatoChlorotic StuntVirusSPFMV SweetPotatoFeathery MottleVirusSPMSV SweetPotatoMild SpecklingVirus


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Metric Imperial

Length

1millimetre(mm) 0.03937inches(in)

1centimetre(cm) 0.3937inches(in)

1metre(m) 1.0936yards(yd)

Area

1hectare(ha) 2.4711acres(ac)

Volume

1litre(l) 35.195fluidounces(floz)

1gallon(gal) 4.5461liters(l)

Weight

1gram(g) 0.0353ounces(oz)

1kilogram(kg) 2.2046pounds(lbs)

1tonne(t) 0.9842ton(t)

Conversion table

SPVG SweetPotatoVirusGSRC ScientificResearch Councilt tonne(s)UK UnitedKingdomUS UnitedStatesUSA UnitedStatesof America

USDA UnitedStatesDepart mentofAgricultureUWI UniversityoftheWest IndiesVit VitaminWI WestIndiesyd yard(s)


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Figure1 Valuechain 3

Figure2 Worldproductionofsweetpotato(1998-2007) 6

Figure3 EUsweetpotatoimports(2002-2008) 8

Figure4 UKsweetpotatoimports(2002-2008) 8

Figure5 UKsweetpotatoimportsfromJamaica(2002-2008) 9

List of figures

List of plates

Plate1 PopularvarietiesfromBarbados 12

Plate2 PopularvarietiesfromJamaica 13

Plate3 PopularvarietiesfromSt.KittsandNevis 14

Plate4 PopularvarietiesfromSt.VincentandtheGrenadines 15

Plate5 PopularvarietiesfromTrinidadandTobago 16

Plate6 Ridgespreparedforplanting 18

Plate7 Sproutedsweetpotatostorageroot 19

Plate8 Sweetpotatonursery 19

Plate9 Micro-propagationofsweetpotatothroughtissueculture 19

Plate10 Sweetpotatocuttingswithshortinternodes 20

Plate11 Sweetpotatocuttingswithlonginternodes 20

Plate12 Cuttingsshowingnodalroots 20

Plate13 Driplinesestablishedbeforeplanting 22

Plate14 Mini-sprinklersirrigatingsweetpotato 22

Plate15 Lifestagesofthesweetpotatoweevil,Cylas formicarius (Coleoptera:Apionidae) 24

Plate16 Featuresofthepheromonetrapusedinthemanagementofthe sweetpotatoweevil,Cylas formicarius(Coleoptera:Apionidae) 25

Plate17 VarioustrapdesignsusedintheIPMofthesweetpotatoweevil, Cylas formicarius(Coleoptera:Apionidae)intheRegion 25

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Plate18 AdultstageanddamagecausedbytheWestIndiansweetpotato weevilEuscepes postfasciatus(Coleoptera:Curculionidae) 26

Plate19 LifestagesanddamagecausedbywhitegrubsPhyllophagaspp (Coleoptera:Scarabaeidae) 27

Plate20 Lifestagesanddamagecausedbythesweetpotatoleafbeetle Typophorus nigritus viridicyaneus(Coleoptera:Chrysomelidae) 28

Plate21 Stemborer,Megastes grandalis(Lepidoptera:Pyralidae) 29

Plate22 Virussymptomsinsweetpotato:stunting,bunching,chlorosis,vein clearing,yieldingreduction 33

Plate23 Whiteexudatefromamaturesweetpotatostorageroot 34

Plate24 Sweetpotatovinesclearedfromtheridgesinpreparationforthe harvester(manual) 35

Plate25 Harvesterup-rootingthesweetpotatoes(mechanical) 36

Plate26 Storagerootsexposedforselection 36

Plate27 Exposedstorageroots 36

Plate28 Harvestedcrop(manual)beingplacedinfieldcratestobetransported fromthefield 36

Plate29 SweetpotatoproductsmanufacturedinJapan(flour,juices,alcohol, candy) 39

Plate30 ProductsmadebytheFoodTechnologyDepartmentoftheScientific ResearchCouncil(SRC),Jamaica 39

Table1 Caribbeansweetpotatoproduction(tonnes)for2006 7

Table2 Estimatednutrientsremovedbythesweetpotatocrop 23

Table3 NutrientprofileofsweetpotatovsIrishpotato 38

Table4 Varietalsuitabilityforvalue-addedproducts 40

Table5 Anexampleoftheinformationrequiredtocalculatethecost ofproduction 43

List of tables

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This Technical Manual is intended to provideproducerswithguidelinesforcultivatingsweetpotato,Ipomoea batatas(L.)Lam.,acropwithgrowingimportancewithintheRegion.Recent-ly, many countries have embraced this com-modityasasubstituteforimportedcerealsandgrainsand forattainingnational food securitygoals. The crop is also an important incomeearnerformanyruralfamiliesandaforeignex-changeearnerforcountries.Assuch,thereisagrowingdemandforthecommodity.

This manual provides a comprehensive over-viewoftheproductionandmarketingaspectsofsweetpotato.Theinformationpresentedisfromacombinationofsourcesincludingresultsof research and development activities con-ductedbytheCaribbeanAgriculturalResearchandDevelopmentInstitute(CARDI).

Thevarioussectionswerewrittenbyscientistsfrom the CARDI root and tuber commoditygroup, amultidisciplinary teamwhich contin-uestogenerate,validateandtransfertechnolo-giestoimprovethecompetivenessofsweetpo-tatoandthelivelihoodofproducersandotherkeystakeholdersalongthevaluechain.

Preface

It is hoped that this publication will providecurrentandpotentialproducerswithpracticalinformation that will assist in increasing pro-ductionandproductivityofthecrop. It isalsohopedthattherewillbeanexpandedviewofsweet potato by industry stakeholders; frombeingaprimaryproducttoonewithhugepo-tentialforvalueaddition.

Thanks to Rohan McDonald (Agricultural Of-ficer - Tissue Culture,Ministry of Agriculture,Forestry and Fisheries, St Vincent and theGrenadines) who provided invaluable techni-cal information.CARDIalsoacknowledges themanystaffmemberswhoassisted indevelop-ingthisSweetPotatoTechnicalManual.Theau-thors,reviewers(BruceLauckner,ClaudettedeFreitas,OpalMorris,RaeannBeckles),designer(Elizabeth Hamilton) and other technical per-sonneltoonumeroustomention.

CARDIextends thanks to theTechnicalCentrefor Agricultural and Rural Cooperation (CTA)whichprovidedfundingforthistechnicalman-ual(2-6-21-102-9)aspartofitssupporttoim-provingtheInstitute’soutreachandcommuni-cation.


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Great potential exists for the development ofthe sweet potato industry in the Caribbean.Sweetpotatoisparticularlyattractiveasacropbecauseofitsadaptabilitytodifferentgrowingconditionsandlowsusceptibilitytonaturaldi-sasterslikehurricaneswhichplaguetheRegion.Thegrowingmarketpotentialforthecrop,asitisnowrecognisedasahealthfoodwithsignifi-cant antioxidant and antimicrobial properties,hasalsocontributedtoitsattractiveness.

Sweet potato is grown throughout the Carib-bean,inthemainbysmallfarmers,usuallyonmarginal land.Productivity isbelow theagro-nomicpotentialofthecropandthereislimitedexportandcropdiversification.Theseobserva-tionsareattributedinparttothegenerallypooragronomic practices conducted by producersandthehighincidenceofpestswhichresultininconsistentqualityoftheharvestedcrop.Poormarketintelligenceandthelimitedknowledgeofmarketopportunitiesandthepotentialusesofthecroparealsocontributoryfactors.

Developing a sustainable and competitive in-dustrythereforerequiresasignificantincreaseintheproductionandproductivityofthecrop.Thegeneration,validationandtransferofsuit-able technologies and the strengthening ofservices to support industry development arethereforecritical.

Towards this goal, stakeholderswithin the in-dustryhaveidentifiedseveralresearchandde-velopment interventions which are necessary

Introduction

Figure 1: Value chain

for industry development. These include: theconservation of local landraces, an improvedknowledgeoftheagronomyofthecrop,iden-tificationof suitablepestmanagement strate-gies,improvedpostharvesthandlingandstor-agesystems,valueaddedproductdevelopmentandanassessmentofthemarketopportunitiesofthecrop.

Thismanualseekstoprovideinformationthatwillassistproducersandotherkeystakeholdersalongthevaluechaintoimprovetheproductiv-ityandproductionofsweetpotato.Themanu-alispresentedwithrespecttothevaluechainandprovides information relating to the criti-cal components of marketing, input supplies,production,harvesting,postharvesthandling,freshmarketandvalueaddition.


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estdiversityofsweetpotatogermplasmisinColumbia,Ecuador,GuatemalaandPeru.Thecrop is grown in several countries globally,but production primarily occurs in tropicaland sub-tropicalareaswhere it is an impor-tantstapleinthedietsofmanypeople.

Ecology

The crop is highly adaptable and is ableto grow in a wide range of agro-ecologicalzones. It grows best in the tropics between40°northand32°south.Temperature,light,rainfall, soil and altitude are themain envi-ronmentalfactorsthataffectthegrowthanddevelopmentof theplant.Optimumgrowthrequiresmeantemperaturesof24°C(75°F)orabove,750-1250mm(30-50inches)ofrainfall,abundantsunshineandmoistnights.Theplantisbetteradaptedtoseasonalvaria-tions characterised by wet and dry seasonsratherthanbywarmandcoldseasons.

Crop growth cycle

The sweet potato plant has three growthphaseswhich aremore or less distinct. Theinitial phase is characterised by slow vinegrowth and rapid growth of adventitiousroots. The first20daysof this initialphaseare important as they determine the totalnumberofstoragerootsformed.Aninterme-diatephasefollowswherethere istherapid

Botanical description

Thesweetpotato,Ipomoea batatas(L.)Lam.is adicotyledonousherbaceous trailing vinewhich is the only economically importantmember of the family Convolvulaceae. Theplant is generally characterised by starchy,succulent and tuberous storage roots; alter-nating palmately lobed leaves andmedium-sized sympetalous flowers which grow in-dividually and vary in colour from white tovaryingdegreesofpurple.

Theplantisaperennialbutisgrownasanan-nual by vegetative propagation using eitherstorage roots or stem cuttings. Its growthhabit ispredominantlyprostratewithavinesystem that rapidly expands horizontallyon the ground. The types of growth habitof sweet potatoes are erect, semi-erect,spreadingandveryspreading.Therearesev-eral hundred varieties with varying formsandgrowthhabits.Themostdominantformshavetwiningandtrailinglongstemsofslen-dertomoderatethicknessandmoderatelytowidelyspacedleaves.

Origin and distribution

Available archaeological, linguistic and his-toricalevidenceindicatesthatthesweetpo-tato originated in or near Central AmericaandnorthwesternSouthAmerica.Thegreat-

1 The sweet potato crop


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thefinalstagethereisbulkingofthestorageroots,which can reach amaximumafter 90days. Storage roots enlarge throughout thelife of theplant but after 120days enlarge-mentpeaks.Itshouldbenotedthatmostofthegrowthphasesarecontrolledgenetically(i.e. variety) and environmentally (i.e. agro-ecological conditions of the areawhere thecropisestablished).

growthofvinesandanincreaseinleafareaaswellasstoragerootinitiation.By100daysaf-terplanting(DAP),theleafareaisatitsmaxi-mumandany further increase inbiomass isdue to storage root formation. The deposi-tionofstarchwithinstoragerootscanoccurasearlyas8DAPandstoragerootformationcanbevisibleasearlyas28DAP.By49DAP,80%ofthestoragerootscanbeidentified.At


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Introduction

To successfully compete in contemporaryagrifoodmarketsnecessitateseffectivemar-ketingstrategies.Inthe21stcentury,afarm-er cannot rely on planting a crop hoping tofindamarketatharvesttime.Theremustbeaparadigmshiftfromaproduction-orientedagriculturalsectortoamarket-orientedsec-torsothatCaribbeanfarmersareabletoex-ploit thenumerousopportunitiesoffered intheglobalmarketplace.

Aligning fresh produce chains to the needsof consumers/customers and developing asystem that is responsive to changing cus-tomerneedsisamustforsuccessintoday’scompetitive business environment. In thecase of sweet potato given the multiplicityofvarietiesgrownintheCaribbeanandtheir

numerous uses, clearly identified marketsare a must before production commences.Sweet potato uses, include conveniencefood, snacks, puree as an additive to soupsand baby foods, nutraceutical, animal feed,aswellasa staple food inmanydiets.Vari-etal selection for specific use and targetedmarketisofcriticalimportance.

2.1 Sweet potato production

World overview

Global sweet potato production decreasedover the1998 - 2007period (Figure2). Theproduction level in 2007 is approximately20%lowerthanin1998.ThetopthreesweetpotatoproducersfortheperiodwereChina,NigeriaandUganda.In2007,Chinaproduced78%oftheworld’ssweetpotatoes.

2 Marketing and supply response

Source:FAOSTAT

Figure 2: World production of sweet potato (1998 – 2007)


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Caribbean overview

The statistics for the Caribbean as a wholefor sweet potato production are not read-ily available from any one source; however,using multiple sources Table 1 provides anillustrationofproductionin2006.Worldpro-ductionfor2006was105milliontonnes(104milliontons).Caribbeanproductionwasonly0.03%ofworldproduction.

2.2 Markets

The U.S.A. market is not open for sweetpotato produced in the Caribbean, conse-quently themaindevelopedcountries’mar-ketsavailableareCanadaand theEuropeanUnion (EU). Figure3 illustrates the importa-tionof sweetpotatoes to theEU for 2002 -2008.Overtheperiod, importsdisplayedanincreasingtrendwithanincreaseofcloseto200%overthesevenyearperiod.

The top three exporters of sweet potatoestotheEU in2008wereUnitedStates, Israel

and Honduras. It is important to note thatHondurashasonlyrecentlyembarkedontheproductionofsweetpotatoesforexport,asadiversificationcrop,andinlessthan10yearstheyhavebecomethethird largestexportertotheEU.In2008,thetopthreecountriesex-portedatotalof50,680tonnes(49,879tons)ofsweetpotatoorapproximately89%oftheimportstotheEU.

During the period under review the UK, acountry with which most CARICOM stateshavealonghistory,wasthelargestimporterintheEU.Figure4providesanillustrationoftheUK imports for the period 2002 - 2008.As can be observed from the graph,UK im-portsincreasedfortheperiod,withthe2008volumebeingapproximately260%morethanthe2002volume.

Jamaica is the only CARICOM state that hasconsistentlyexportedsweetpotatoes to theUK.Figure5 illustratesUK sweetpotato im-portsfromJamaicafor2002-2008.

Table 1: Caribbean sweet potato production (tonnes) for 2006

COUNTRY

Jamaica

Barbados

St.Kitts/Nevis

Dominica

St.Vincent&theGrenadines

Trinidad&Tobago

Total

PRODUCTION Tonnes (t)

27.5

2.2

0.3

0.3

1.6

0.5

32.4


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Source:MarketAccessDatabase

Figure 3: EU sweet potato imports (2002 - 2008)

Caribbean sweet potato suppliers to Britishretail chains must comply with EurepGAPstandards. Issues such asmaximum residuelevels and traceability are critical. In addi-tion,manysupermarketsindevelopedcoun-tries have implemented private standardsof which small producers in the Caribbean


Figure 4: UK sweet potato imports (2002 – 2008)

mustbeaware.Asconsumersbecomemorehealthconscious,greateremphasisisplacedonconsumingnaturalhighnutritionalfoods.Orange flesh cultivars of sweetpotato, con-tainingahighconcentrationofcarotenoids,aprecursorofvitaminA,arearegularfeatureoncontemporarysupermarketshelves.

EU market


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Figure 5: UK sweet potato imports from Jamaica (2002 - 2008)

2.3 Marketing

2.3.1 Buildingthemarketplan

Therearemanydifferentmarkets forsweetpotatoincludingfreshorprocessed;domes-tic,regionalandextra-regional.Therequire-mentsofdifferentmarketsvarywidely.

Building amarket plan for sweetpotato re-quires a clear identification of the targetedmarket. The use of the product in the tar-getedmarkets canbe fresh, valueaddedorindustrial (e.g. animal feed, starch). In theRegionthemajormarketisforfreshproduceconsumption.

2.3.2 Guidelinesformarketing

Anindepthassessmentofthemarketsshouldbeconductedtoassisttheproducertoselectproduction systems which are appropriateformarketpenetrationandsustainability.

The followingpointers areoffered toCarib-bean sweet potato growers attempting topenetrate regional and extra-regional mar-kets:

• Identifythetargetmarket

• Determine the volumes required by themarketincludingpossiblechangesinpro-ductionvolumesovertime

• Identifythebuyer(s)

• Determinethevolumesthebuyeriswill-ingtotakeandthefrequencyofpurchase

• Determine and follow the guidelines ofthebuyers.Theyknowthetargetedmar-ket segment (i.e. varieties, productionand post-harvest practices inclusive ofpackagingrequired)

• Buildstrongrelationshipsalongthevaluechain


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• Produce consistently high quality sweetpotatoesatcompetitiveprices

• Ensure thatquantitiesproducedare suf-ficientforthemarket

• Keep abreast of the changes in the re-quirements of the market, as they aredynamic.As such, it is also important tolinkintoamarketsystemwhichprovidesupdatedmarketintelligenceinformation


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Globally, great strides have been made tobreed sweet potato varieties to meet thewide range of requirements of products forwhichtheyareutilised.China,JapanandtheUSAareleadersinthisarea.TherehavebeenfewbreedingandselectioneffortsintheCa-ribbean.

Within the Region, most introductions ofsweet potato varieties were obtained fromthe United States, the International PotatoCenter (CIP), the Asian Vegetable Researchand Development Center (AVRDC) and theInternational Institute for Tropical Agricul-ture (IITA). Inaddition, landraceshavebeenselectedandconserved.Someoftheseland-raceshavealsobeencollectedbytheinterna-tional centres and characterised, conservedandincludedintheirbreedingprogrammes.

Selection and evaluation of local and intro-duced clones in the Region have been con-ducted by farmers, the Ministries of Agri-culture, andother institutions, such as, TheUniversityof theWest Indies (UWI)and theCaribbean Agricultural Research and Devel-opmentInstitute(CARDI).

Currentlytherearegermplasmcollectionsina few countries within the Region, some ofwhich have been evaluated and character-ised.ActivitieswithintheCaribbeanhavefo-cusedonidentifyingthebestclonestomeetfresh market demands and more recentlythe processing market. However, the char-acterisation and nomenclature of landraces

in thevariousCaribbeancountries, is still initsinfancy.Thereismuchconfusionsincedif-ferent names are given to the same clonesand there are little data on morphologicalcharacters.Work is needed to describe andcataloguethesweetpotatogermplasmintheRegion.

Selection of the sweet potato variety/ies for commercial production

• Determinethesweetpotatovarietyorva-rietiesrequiredbythetargetmarket(i.e.,fresh, processed, local, regional and ex-tra-regional). The freshmarketdemandsare different from those of the process-ing industry. In the former, some of thecharacters of importance are taste, size,shape, skinand flesh colourof the freshtuberous roots. The processor, on theotherhand,focusesonthechemicalcom-positionofthetuberousroots(Plates1-5).

• Select the variety with a high degree ofadaptabilitytotheagro-ecologicalcondi-tionsoftheproductionarea.Thechosenvariety or varieties must produce highquality yields notwithstanding pests,droughts, floods and other environmen-talproblems.

• Ensurethattherearesufficientquantitiesofcleanplantingmaterialoftheselectedvarieties.

Germplasm selection 3


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C104 Black RockA26/7

CBS49 Caroline Lea86BM15

Sugar Country LeanRed Man

Plate 1: Popular varieties from Barbados


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Quarter Million EustaceMinda

Sidges Blue Bud Fine LeafDor

Fire on Land Yellow BellyClarendon

Plate 2: Popular varieties from Jamaica


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Pumpkin Sugar RootRSGF

LRS07 Taiwan

Plate 3: Popular varieties from St Kitts and Nevis


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Plate 4: Popular varieties from St. Vincent and the Grenadines

Lovers Name Black VineWilliam White

Hubert Red Devil William Break FallKizzie Red

Kizzie White Big RedWilliam Blue Top


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Plate 5: Popular varieties from Trinidad and Tobago

Bugs Bunny Chicken FootCarrot

Jewel C99O49

TIS 9191 Never MissTIB 9 TIS 3194


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4.1 Pre-production

Pre-production involves the practices andprocedures that precede the establishmentof the cropandare critical for ensuringop-timal growth and development. It includesprimarily,siteselectionandlandpreparation.

Siteselection

Soil.Welldrainedsandyorsandy loamsoilsarebestforsweetpotatoproduction.Heavyclaysandsoilshighinorganicmatterarenotrecommended. Heavy clay soils retard rootdevelopmentand result inpoor root shape.Highorganicmatter leads to abundant vinegrowthandpoorstoragerootdevelopment.Fields with high nematode populationsshouldalsobeavoided.Ingeneral,fieldsthathavenotbeenusedforsweetpotatoesinthelast2-3yearsarepreferred.

Sweet potatoes are sensitive to alkalineor saline soil; hence, these soils should beavoided. To achieve high yields, the soilwithintheplantingareashouldhaveapHbe-tween5.8and6.4.IfthepHofthesoilislow,limeshouldbe incorporatedto increasethepH. Theapplicationof limeshouldbedonetoallowsufficienttimeforthesoilpHtobeincreased.

Soil testing.Soiltestsmustbecarriedouttodeterminethenaturalfertilityofthesite.In-terpretationof the results should guide the

fertilitymanagement strategy that is imple-mented.

Rainfall.Regions/zoneswithanannual rain-fallof750-1250mm(30-50in)perannum,withabout500mm(20in)fallingduringthegrowingseason,arebestsuitedforsweetpo-tatoproduction.Althoughthecropcanwith-standdrought conditions, yields are consid-erablyreduced ifadryperiodoccursduringthefirst6weeksafterplanting.

Temperature.Sweetpotatoisawarmweath-ercrop.Itgrowsbestatmeantemperaturesabove 24 °C (75 °F) and requires abundantsunshine.Itisthereforenotrecommendedtoplantsweetpotatoesinshadedconditions.

Landpreparation

Sweetpotato isusuallyplantedonridgesormounds.Ridgesareusually75-90cmwide(30 -36 in)and30 -45cm(12 -18 in)highandmounds40cm(15in)atthebaseand20-30cm(8-12in)high.Onflatterrain,landispreparedmechanically and on sloping land,ridgesaremademanuallyalongthecontours(Plate6).

Ploughed and harrowed (well worked) bedsprovide the developing rootswith loose fri-able soil so that they can expand to theirpotentialsizeandshapewithoutrestriction.Thesemethodsoflandpreparationallowad-equatedrainageandmakeharvestingeasier.

Production 4


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Themainconsiderationisthatthedevelopingrootsremainunderthesoilwithinthehill.Ifusingamechanicaldiggeratharvesttime,itisimportanttomatchthewidthofthemoundwiththewidthofthedigger’smouth.

The advantages of planting on ridges andmoundsare:

• Higherandbetterqualityyield

• Preventionofsoilerosion

• Productionoflargerstorageroots

• Lesspossibilityofdeformedstorageroots

• Easierharvesting

• Moreefficientpestmanagement

4.2 Crop establishment

Theestablishmentofasweetpotatocropin-cludes thepropagation aswell asmeasuresnecessary for ensuring a high yielding goodquality crop. Such measures include irriga-tion,fertilityandpestmanagement.

4.2.1 Propagation

Itisimportanttoselecthighqualityplantingmaterialtoensuretheproductionofagoodcrop. Sweet potato can be propagated in avariety of ways; tissue culture, sprouting,vine cuttings and seeds. Vine cuttings andsproutsand,toalesserextent,tissuecultureare the most commonly used propaguleswithintheRegion.

4.2.1.1 Propagation material (propagules)

Vine cuttings

Traditionally, many growers utilise the cut-tingsfromthepreviouscroptoestablishnewcultivations of sweet potato. As with mostvegetatively propagated crops the qualityoftheplantingmaterial impactsgrowthandresultant yield. It is therefore critical in theestablishment of new cultivations that highqualityplantingmaterialbeused.

Generally, vine cuttings/slips ranging inlengthfrom30cmto40cm(12-15in)shouldbe planted. The apical region of the plantshouldbeusedasitismorelikelytobefreeofpestinfestationsanditgivesbetteryieldsthancuttingsfromthemiddleorbaseoftheplant(Plates10and11).Theimplementusedto cut the vines should be sharp and clean.Thelowerleavesofthevines/slipsshouldbecut as tearing may damage the nodes thatcouldeventuallyproduceroots.

Sprouting

Sprouting involves the use of small to me-dium sized storage roots to obtain slips forplanting.Storagerootsselectedforsprouting

Plate 6: Ridges prepared for planting

Ridges prepared manually on

flat land

Ridges prepared manually on sloping land


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shouldbefreeofpestsandwashedcarefullywithadisinfectantbeforeplanting(e.g.20%bleach solution). Sweet potatoes selectedshould be cut crosswise into two or threesections to increase the number of sproutsproduced.Toavoidspreadingviruses,cuttingknivesshouldbedisinfected.

Cutrootsshouldbeplantedinanurserybedthatislocatedinanareawherethereisgooddrainage. To prevent contamination, thenursery bed shouldbe established far awayfromexistingsweetpotatofields.Toprepareplantingmaterial foronehectare,anurserybedofapproximately35m2(400ft2)isneed-ed.

Storage root sections should be establishedin the nursery bed, close together but nottouching.Storageroots (sections)shouldbecovered with about 5 cm (2 in) of soil andthena layerofmulchaddedtoretainmois-ture.Sweetpotatovinesshouldnotbeusedasmulch.Waterisnecessarytokeepthesoilmoist, but notwet.When the sprouts havegrownto40-50cm(15-20in),theyshouldbecutandusedtoestablishthecrop.Thisisapproximately4-8weeksafterbedding.

Plate 7: Sprouted sweet potato storage root

Plate 8: Sweet potato nursery

Tissue culture

Tissue culture is the rapid propagation ofplantswithinacontrolledenvironment.Thisprocessinvolvesthegrowingoftinypiecesoftheplant(explants)onsolidorliquidnutrientmedia. Plantlets obtained are placed undershelteredconditionstoundergoweaningandhardening and then transferred to the field(Plate9).Thispropagationmethodensuresaconsistentandcleansourceofplantingmate-rial.

Plate 9: Micro-propagation of sweet potato through tissue culture

(A-C:culturingofplantlets,D-F:hardeningandweaningofplantlets

undershelteredconditions)

A B C

FED


20

Storage of planting material

When vine cuttings/slips cannot be plantedimmediately,theycanbestoredunderdamp/shadedconditions forup to7days.Note, ifthevinecuttingsarebeingstoredthemajor-ityof leavesshouldberemovedwithonlyafewleavesbeingleftatthetip.Thecuttingsshouldbetied inabundleandthecutendscoveredatthebasewithadampcloth.Dur-ingthisperiod,rootswillbegintogrowatthenodesandthecuttingswillbecomemorere-sistanttothe“shock”ofplanting(Plate12).

4.2.1.2 Planting

Time of planting

Underrainfedconditions, it isbesttoplantsweetpotatoesearly in the rainy season sothatestablishmentcantakeplacequickly.Inareas where the rainy season is prolonged,plantingmaybetimedsothat thecropma-turesjustastherainfallbeginstodecline.

Transplanting

Vine cuttings should be planted at about a45°angle,asthispromotesevenrootdevel-opment.Halfof thecuttingor threeto fournodesshouldbeburiedataspacingof25-30cm(10-12 in)betweenplants.Onaverage,depending on the spacing 30,000 - 35,000cuttings are required per hectare (12,000 -14,000perac).WithintheRegion,plantingisusuallymanual.Thiscanbeassimpleaspush-ingthecuttingsintomoundsorridgeswithaforkedstick.Cuttingsshouldbewateredatorimmediatelyafterplanting.The field shouldberoutinelymonitoredduringthefirst2-3weekstoreplaceanydyingplants.Ifthemar-ket secured requires produce at intervals,theplantingshouldbestaggered.

Plate 10: Sweet potato cuttings with short internodes

Plate 11: Sweet potato cuttings with long internodes

Plate 12: Cuttings showing nodal roots


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4.2.2. Irrigation

Although sweet potatoes are deep rootedanddroughttolerant,theystillrequiresuffi-cientmoisture to grow and produce qualitystorageroots.Watersupplyfluctuationscancausethedevelopmentofsmallandmisshap-en roots. These fluctuations can also causegrowth cracks. These defects will impactupon the marketability of harvested sweetpotatoes.

In contrast, excessive moisture can causevigorous vine growth and elongated roots.However,yearroundproductionofsweetpo-tato(includingproductioninthedryseason)is required for sustained markets and foodsecurity. Year round production thereforerequires irrigation for dry season produc-tion.Twotypesofirrigationsystemsarerec-ommended,thedriptape(Plate13)andthemini-sprinkler(Plate14).

Drip irrigation

During dry periods, drip irrigation is impor-tant for sustaining yields and is an efficientmethodofprovidingtherequiredamountofwaterattheappropriatetime.

Mini-sprinklers

Another option for providing the requiredmoisture to the plant is mini-sprinklers.Yields are improved under this system. Thisisattributedtomorevigorousgrowthduetotherootingofvinenodesonthewetsoilbe-tweenthebeds.However,itshouldbenotedthat there is more weed growth under thissystem.

Thebestway tomaintain the desiredmois-ture content is tomonitor the soilmoisturewith tensiometers; these instruments pro-videan indicationofwhenandhow long toirrigate.Thewaterrequirementwillvarywiththesoiltypeandthecropstage.

Moisturelevelsareespeciallyimportantfrom10 weeks onward as storage roots start toenlarge (bulk-up). Fluctuating soil moisturelevelsduringthisstagewillreduceyieldandcausecrackingofroots.

4.2.3 Fertility management

Sweet potatoes require nitrogen, phospho-rous, potassium and small quantities of bo-ron,calciumandmagnesium.Nitrogenisre-quiredfortheinitialgrowthoftheplantbutexcess application leads to abundant vinegrowthandreducedstoragerootformation.Potassiumiscriticalforstoragerootdevelop-mentwhereasphosphorousislinkedtoyield.

The recommended fertiliser rate for sweetpotatoproduction isbasedoncrop removal(Table 2). Potassium is the element that ismostlyremovedbythecrop.Completefertil-izers(NPK)usedonthecropshouldthereforesupply adequate amounts of each of thesecritical elements. Fertiliser should be incor-porated at land preparation and when thevinesstarttorun.


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Plate 13: Drip lines established before planting

Plate 14: Mini-sprinklers irrigating sweet potato


23

Source:Traynor2005,Rao1991,Ngeze2000

ELEMENT

Nitrogen

Phosphorous

Potassium

CROP REMOVAL (kg/ha)

70-100

40-90

100-210

methodsandonly relieson chemicalswhenall othermethodsprove tobe ineffective inprotecting the crop. IPM aims at ensuringthatthefarmergetsthebestpossiblereturnsandtheenvironmentisprotected.Therearemanydifferentoptions tomanagepests im-pacting sweet potato, they include: culturalpractices, biological control, physical andmechanicalmeasures and chemical applica-tions.Legislationisalsoanoptiontoreducethemovementofinfestedmaterialfromonecountrytoanother.Theintegratedapproachrelies on informed decision making in that,a decision is only made after informationis collected (i.e., crop stage, pest type andnumbers,productionpractices,prices,inputsavailable, tools available). Integrated man-agementiscriticalforthesustainedmanage-mentofpests and theachievementofopti-malproduction.

Major pests

Although all classes of pests are associatedwiththesweetpotatocrop,significantlossesinyield(qualityandquantity)areattributedmainly to insects. With emphasis on thispest grouping, life cycles andpossibleman-agementstrategiesforsomeofthereportedpestswithintheCaribbeanarediscussed.

Insects

Several insect species attack the leaves,stems and storage roots of sweet potato.However,onlyasmallnumberareviewedaseconomically important and warrant inten-sivemanagement.ImportantinsectpestsintheCaribbeanarethesweetpotatoweevils,(Cylas formicarius, Euscepes postfasciatus),

Table 2: Estimated nutrients removed by the sweet potato crop

4.2.4 Pestmanagement

Sweetpotatoproductionisaffectedbypestswhichsignificantly reduceboththequantityandqualityofyields.Someproducerswithinthe Caribbean have reported losses due topests reaching as high as 60 - 100% of har-vestedyields. Theterm“pest”referstoanyunwanted plants or animals that negativelyaffect the crop and includes insects, mites,fungi,viruses,bacteriaandweeds.

Beforepestscanbemanaged,itisimportantthat there is proper diagnosis so that themostappropriateandeffectivestrategiescanbeimplemented.Thereforeitisnecessaryforfarmerstoinspectthecroptodeterminethepresence of pests, their numbers, and thelevelofdamagetothecrop.

Oncediagnosishasbeencompletedaninte-gratedmanagementstrategyshouldbeiden-tifiedtoreducepestnumbersanddamagetothecrop.IntegratedPestManagement(IPM)refers to themanagement of pests throughtheuseofacombinationofcompatible tac-tics.IPMemphasisestheuseofnon-chemical


24

with excretement. Fully grown larvaepupate and adults emerge from thestemsand/orroots.Asaresultoffeed-ing,theplantproducesterpenoidsthatrenderthesweetpotatounpalatable.

Management

The management of C. formicarius consists of a combination of culturalpractices and the trapping of weevilswith a sexpheromone (physicalmea-sure).

Cultural practices:Therearecropman-agement practices that help preventthe entry and/or reduce the numberofweevils in the crop. Suchpracticesinclude:

• Usingcleanplantingmaterial

• Removing alternate hosts (such asmorningglory, “wildslip”, Ipomoeaspp.)

• Conducting field sanitation (de-stroyingoldsweetpotatofields,re-movingcropresidues)

• Ensuringadequatesoilmoisture

• Molding/hilling plants to reducecracksinthesoilarea

• Harvestingpromptly

• Rotatingthecrop

• Usingtolerantvarieties

whitegrubs(Phyllophagaspp.),sweetpotatoleaf beetle (Typophorus nigritus viridicyane-us)andthestemborer(Megastes grandalis).

Rootfeeders

♦ Sweetpotatoweevil,Cylas forimicari-us(Coleoptera:Apionidae)

The sweet potato weevil, Cylas for-imicarius, isoneof themostdestruc-tivepestsofsweetpotatoworldwide.Adult females lay eggs in stems and/or thesurfaceof the roots justunderthe skin. The eggs hatch and the lar-vaetunnelintovinesandrootswheretheyfeedanddevelop.Thelarvalfeed-ingresultsintunnelswithinthesweetpotato; often the tunnels are filled

Plate 15: Life stages of the sweet potato weevil, Cylasformicarius (Coleoptera: Apionidae)

Adult

Larvae

Pupae


25

Physical measures - trapping:Thesec-ond component of the managementstrategyreducesthenumberofsweetpotato weevils through trapping.Trapsarebaitedwitha chemical thatattracts male sweet potato weevils.The chemical known as a sex phero-mone, is produced by femaleweevilsfor mating purposes. In response tothe chemical (sex pheromone) placedin the trap, males move towards thebaited traps, enter and drown in acontainer inwhichthere isasoapso-lution. In time, as the male weevilsare removed, less mating occurs andthereforefewerweevilsareproduced.

Thekeyfeaturesofthetrapinclude:

A. the sex pheromone (attractant)which is impregnated on a dis-penser(e.g.rubbersepta).Ahighdose pheromone is used in ordertomasstraptheweevils

Plate 16: Features of the pheromone trap used in the management of the

sweet potato weevil, Cylasformicarius (Coleoptera: Apionidae)

B. a container for catching themaleweevilsthatenterthetrap

C. a frame onwhich the trap is sus-pended

Traps designs range from simple andinexpensive to complex commercialdesigns.

Regardlessofthetrapdesign,thecriti-calfactorsforthepheromonetrappingsystemtoworkefficientlyare:

• sufficientairvents toallowthedif-fusionofthescenttospreadacrossthefield

• a catchment container that is deepenoughtopreventtheweevilsfromescaping

• aframewhichallowsthetrapheighttobeadjustedinrelationtothecropcanopy

Thetrapshouldbeplaced inthefieldassoonasplanting iscompleted. It is

Plate 17: Various trap designs used in the IPM of the sweet potato weevil, Cylasforimicarius

(Coleoptera: Apionidae) in the Region


26

Management

The management of the West Indiansweetpotatoweevilismainlythroughcultural practices and chemical appli-cations.

Cultural practices: The recommendedpracticesaresimilartothoseoutlinedforthesweetpotatoweevil,C. formi-carius (seeabove).

importanttoplacethetrapjustabovethecanopy.Thetrapshouldbemovedaround the field every week and thepheromone bait changed every 6 - 8weeks. One or two traps should beplaced within a hectare of sweet po-tato.

Biological control: There have beenpromising studies thatdemonstrateareduction in weevil populations anddamage to the crop with the use ofentomopathogens (fungi and nema-todes) andarthropodpredators, suchas,ants.

♦ West Indian sweet potatoweevil,Eu-scepes postfasciatus(Coleoptera:Cur-culionidae)

TheWest Indiansweetpotatoweevil,Euscepes postfasciatus, has a simi-lar life history to the sweet potatoweevil, C. formicarius. Females layyellow-greyish eggs singly in a cavityexcavated in the roots/stems; rootsare thepreferred site foroviposition.Larvae tunnel, feed and grow withinroots/stems. Fully grown larvae en-ter a resting stage (pupa), thereafter,adultsemerge.E. postfasciatusadultsarenotasdistinctiveasthoseofC. for-micarius; they resemble soil particlesandarehardtodetectinthesoil.Thebodyoftheadulthasshorterectbris-tles and scales are reddish brown tograyishblack.Theplantproducester-penoidsasaresultofthefeedingandthe damage results in discoloration.Adultsfeedonsweetpotatotissueandemergebychewingexitholes.

Chemical applications:Recommendedchemical applications include the useofsystemicinsecticides;however,careshouldbe taken to ensure that appli-cationsaremadewithintheguidelinesofthemanufacturersoastoavoidanyresiduesontherootsatharvest.

Adult

Sweet potato damaged by larval feeding

Plate 18: Adult stage and damage caused by the West Indian sweet potato weevil, Euscepes

postfasciatus (Coleoptera: Curculionidae)


27

Management

Management of white grubs includesthe use of cultural practices andchemical applications. It is importantto observe the field after it has beenprepared, as grubsareoftenexposedduring land preparation. Early detec-tion and monitoring with light trapscan improve the timing of manage-mentinterventions.

Cultural practices: The removal ofweeds that may harbour the pest isimportant for avoiding infestations.Grubpopulationscanbuilduponlandthat is fallow with weeds. Crop rota-tion andavoiding soilswith excessivelevels of organicmatter are also rec-ommendedpractices.

Chemical applications: Theuseof soiltreatmentswith selective insecticidescanalsobeused in combinationwiththe cultural practices. Utilising insec-ticidessuchasimidacloprid(Admire®)and thiamethoxam (Actara®) duringtheearlystagesofthecropcanreducedamagebywhitegrubs.Toreducetheprobabilityofhavingresiduesonhar-vestedsweetpotatoes,careshouldbetaken to apply at the recommendedratesandensurepropertiming.

Biological control: There have beenpromising studies thatdemonstrateareduction in thepopulationanddam-age to thecropwith theuseofento-mopahtogens(fungiandnematodes).

♦ Whitegrubs(Phyllophagaspp.) (Cole-optera:Scarabaeidae)

SeveralspeciesofwhitegrubsoccurintheCaribbean.Eggsarelaidinthesoilandyounglarvaefeedonorganicmat-ter and later on roots. Larvae gougeout broad shallow areas on the rootthus reducing marketability. Larvaeare “C” shaped, have well developedlegs and range in colour from whitetooff-white/grayish-white,dependingon the species. Theyhavewelldevel-oped legs and a brownhead capsule.Fully grown larvae penetrate the soilandpupate.Emergingadultsfeedonawide rangeofplants (including sweetpotato),butdonotusuallycauseeco-nomic damage. During the day theadults shelter in the soil around thebasesofplants.

Plate 19: Life stages and damage caused by white grubs Phyllophaga spp.

(Coleoptera: Scarabaeidae)

Surface damage by larval feeding

Adult “C” Shaped larva


28

Cultural practices: Prevent the entryof thebeetle intothecropareaby (i)removing weedy areas surroundingthe plotwhichmay harbour the bee-tle,and(ii)moldingthesoiltoreducecracks.Practisingcroprotationcanas-sist in protecting the crop fromdam-age.

Chemical applications: Selective in-secticidesshouldbeusedincombina-tionwith theculturalpractices.Usingtheinsecticideimidacloprid(Admire®)duringtheearlystagesofthecropcanreduce damage by the sweet potatoleaf beetle. To reduce theprobabilityof having residues on the roots, careshould be taken to ensure that therecommendedratesareappliedatthepropercropstage.

Stemborer

♦ Stemborer, Megastes grandalis (Lepi-doptera:Pyralidae)

The stem/vine borer,Megastes gran-dalis(Lepidoptera:Pyralidae)isuniqueto Guyana and Trinidad and Tobagoand is thought to be second in theorder of economic importance to thesweet potato weevil in those coun-tries.Eggsarelaidsinglyorinclustersoflessthanfive;theyarebrightgreenand turn purple at hatching. Newlyhatched larvaefeedonthesurfaceofthe vine or may burrow immediatelyinto the stemwhere they tunnel andfeed.Mature larvae arewhitewith apinkcolourandtheyhaveadarkheadcapsule. Fullygrown larvae spina co-

♦ Sweet potato leaf beetle, Typopho-rus nigritus viridicyaneus (Coleoptera:Chrysomelidae)

ThesweetpotatoleafbeetleTypopho-rusnigritus viridicyaneus (Coleoptera: Chrysomelidae)isanemergingpestofsweet potato. Adult beetles lay eggsat the base of the plant or on lowerleavesneartothesoil.Thelarvaefeedonrootsandtheresultingdamagere-sembles that of thewhite grub. Fullygrownlarvaepupateinanearthencelland adults emerge later. Adults areshiny blue beetles observed on theunderside of leaves as well as withinthesoil.Adultbeetleschewtheleavesbutneverthestemsandcandefoliateplants.

Management

Themanagementofthesweetpotatoleafbeetleincludestheuseofculturalpracticesandchemicalapplications.

Adult Larva and Pupa

Surface damage by larval feeding

Plate 20: Life stages and damage caused by sweet potato leaf beetle, Typophorusnigritusviridicya-

neus (Coleoptera: Chrysomelidae)


29

Chemical applications:Thecrypticna-tureofthisstemborerreducestheef-fectivenessofchemicalapplications.Asystemic insecticide, such as friponly(Regent®)appliedat the recommend-edratecanreduceinfestations.

coon inside the stem. Adults exit thestemsafterapproximately14days.

Damageis insidiousasinfestedplantscan appear symptomless.Damage re-sults from the larva boring from thestem to themain roots. Swelling andsplittingof thestemsandthedepositof frass external to the split stem oron thegroundmaybeobserved.Silk-en threads may also be seen at splitstems.Othersymptomsincludestunt-edplants,leafsheddingandthelackofstoragerootproduction.

Management

Tolerant varieties, cultural practicesand toa lesserextentchemicalappli-cations are the tactics recommendedtomanage.

Tolerant varieties: Differential toler-ance among sweet potato varietieshasbeenreported.Theseobservationshavebeenlinkedto(i)theshapeoftheleafinthat,eggssurvivepoorlyonnar-row leaves when compared to wideleaves and (ii) the ability of theplantto correct the damage to the foodtransportchannelsbythelarvaboringintothestem.

Cultural practices: Molding the croplate in the growth stage, i.e. greaterthan 7 weeks, prevents adults fromexiting the stems. Inaddition, the re-movalofalternatehosts(e.g.,morningglory family) can reduce populationbuild-up.

Sweet potato root damaged by the stem borer larva

Plate 21: Stem borer, Megastesgrandalis (Lepidoptera: Pyralidae)

Sweet potato crown damaged by the stem borer larva


30

Leaffeeders

There are several leaf feeding peststhatoccasionallydamagethecropandmay infrequently require attention.Theseinclude:tortoisebeetles(Metri-ona sp., Chelymorpha multipunctata,Deloyala sp), cucumber beetle (Di-abrotica sp.), armyworm (Spodoptera sp.), hornworm (Agrius cingulatus),leaf webber (Trichotaphe sp.), leafhopper (Empoasca sp.), sweet potatowhitefly (Bemisia tabaci) and thrips(Frankliniellasp).

Management

Field sanitation,handpickingand theuseof“soft”pesticidescanbeusedtoreduceinfestations.PesticidesincludeBacillus thuringiensis (Bt) – entomo-pathogenicbacteria,neem,insecticid-alsoapsandoils.

Diseases

Sweetpotatoissubjectedtoanumberofdis-eases causedbybacteria, fungi andviruses.These pathogens impact yield both in thefieldandinstorageandcanresultinsubstan-tiallosses.Managementisprimarilythroughtheuseofpreventativemeasures.Themostcommonly reported pathogens associatedwith field production in the Caribbean arehighlighted.

Bacteria

♦ Soil rot (Streptomyces ipomoea)

Soil rot (Streptomyces ipomoea) isa bacterial disease of sweet potato.Symptoms are quite distinct and in-

cluderootsdevelopingablacknecrot-ic lesion which sometimes breaks offwhentherootsareharvested.Infectedplantsmay bewilted and/or severelystuntedwith lower leavesbronzedoryellow.

Management

Cultural practices:Removalofoldstor-age roots, crop rotation, the use ofcleanplantingmaterial,andthedisin-fectingoffarmtoolsareall importantpractices for reducing the chance ofinfectingthecropwiththispathogen.

Fungi

Fungaldiseasesthatarecommonlyassoci-atedwith sweet potato in the Caribbeanincludeleafspotsandrusts.

♦ Leaf spots

Leaf spots are caused by the fungalpathogens Cercospora sp., Alternar-ia sp., and Phyllosticta batatas. Leafspots initially showas tiny circular orovalspotsonplantleavesthatexpandwithtime.Thesespotscanvaryinco-lour.Inlaterstagesofthedisease,theleaves may become yellow and fall.Damageto leaves ismostseveredur-ingwetweatherconditions.

Management

Cultural practices: Due to the persis-tence of the fungus in plant residue,


31

reduce yields but have not been shownto impact the quality of sweet potatoes.Symptomsincludeveinclearingormosaic,chlorosis stunting, leaf reduction and de-formation.Thevectorsresponsibleforthetransmissionofvirusesincludeaphidsandwhiteflies.

Management

Cultural practices. Themainmanage-ment approach for reducing viral in-fectionsistheuseofculturalpractices.Suchpracticesincludetheuseofcleanplantingmaterial, rouging of infectedplantsandtheremovalofweedybor-ersthatmayserveasreservoirsforthevirusesandtheirvectors.

Chemical applications: The manage-ment of the vectors of the viruses,thatis,aphidsandwhitefliesassistsinreducing the spread of the infection.Fields should be monitored and ap-plicationsof “soft chemicals”, suchassoapsandoilsusedtoreducepopula-tions.

Nematodes

Nematodes are microscopic worms thatfeed on the roots of sweet potato andcan significantly impact yields. Of note,are root-knot nematodes (Meloidogynespp.). Other species of nematodes havealsobeenassociatedwiththecropandin-clude:Tylenchulus sp.,Radopholus spRo-tylenchulus reniformis, and Pratylenchussp.

fieldsanitationiscriticalformanagingleafspots.

Chemical applications: Leaf spots arenotusuallysufficientlysevere towar-rant the application of a pesticide.However, if the infection is severe arecommendedfungicideshouldbeap-plied.

♦ Rusts

Leaf rust or red rust (Coleosporium ipomoeae)andwhiterustorleafmold(Albugosp.)areofminoreconomicim-portanceandhavenotbeensufficient-lyseveretorecommendmanagement.

Viruses

Worldwide thereareover20viruses thataffect sweet potato. They are thought toreduceyieldsbyupto30%ormore.WithintheCaribbean,viruseshavebeendetectedinsomemajorproducingcountries.Theseinclude in part, Sweet Potato FeatheryMottle Virus (SPFMV), Sweet PotatoMildSpeckling Virus (SPMSV), Sweet PotatoChlorotic Fleck Virus (SPCFV), Sweet Po-tato Chlorotic Stunt Virus (SPCSV), SweetPotatoCaulimo-likeVirus,SweetPotatoVi-rusG (SPVG)andCucumberMosaicVirus(CMV).

Frequently, thevirusesoccur inmixed in-fections. In some cases, these mixed in-fectionscauseasynergisticeffectthatre-sult in a more severe reduction in yieldsthan would be expected if the individualvirusalonewaspresent.Viralinfestations


32

moistandcoveredwithathickplasticfor approximately 2 weeks. The heatbuild-upundertheplasticreducesthesurvivalofthenematode.

Chemical application. In severe infes-tations, a nematicide can be appliedafterallotherpracticeshavefailed.Tobeeffective,thenematicidehastobea systemic so it is important that thechemicalusedisnotverypersistentasthismayresultinpesticideresiduesonthecrop.

Rats

Damagedue to ratscan range from5 -30%oftheharvestedcrop.Managementpracticesincludeplacingbaitaroundtheedgesofthefield toprevent rats fromentering.Exposedroots are themost frequently attacked andas suchensuring that the roots are coveredisimportant.

Weeds

Severalweedspeciesareassociatedwiththesweetpotatocrop.Ifweedsarenotmanaged,theycanimpacttheproductivityofthecropbycompetingforspace,nutrientsandmois-ture.Thecriticalperiodformanagingweedsin sweetpotato isduring the first2monthsof growth. After this period, vine growthshouldeffectively cover the ground surface,thussuppressingweeds.Beforeplantingoc-curs a pre-emergent herbicide can be usedand thereafter hand weeding. If herbicidesarebeingusedaftervineshavetrailed,caremustbe taken toensure that theplantsarenotburnt.

Typically,symptomscanbeobservedbothbelowandaboveground.

Belowground,thesymptomsinclude:

• galls on adventitious and storageroots

• abnormalformationandfunctionoftherootsystem

Non-specific above ground symptomsinclude:

• patchystuntedgrowth

• discolourationandleafchlorosis

• excessive wilting during dry, hotconditions

• stuntingofwholeplants

• reducedyieldandquality

• sometimesprematuredeath

Management

Cultural control: This includes fieldsanitation and crop rotation for twoormore years,where plots are heav-ilyinfested.Theuseofcleanplantingmaterialisalsoimportant.Introducingplantsthatrepelnematodeswithinthesoil,inandaroundcultivatedareas,isalso useful in reducing infestations.Plantswhichrepelnematodesincludemarigoldandneem.

Physical measures: Soil solarisation isaneffectivemethod to reducenema-tode populations. The soil has to be


33

Plate 22: Virus symptoms in sweet potato: stunting, bunching, chlorosis, vein clearing, yield

reduction


34

Post production includes harvesting, han-dling, curing, packaging, storing, shipping,wholesaling,retailing,andanyotheractivitytowhichtheproduce issubjected. Itshouldbenotedthatthepricereceivedforproduceis largely determined by the quality at themarketplace. Therefore the quality at har-vestmustbemaintainedbyproperhandling,packagingandstorageconditions.

5.1 Harvest

Maturityindices

Thecropisreadyforharvestwhentheleavesturnyellowandbegintodrop.Maturitycanalso be assessed by cutting sample roots inthe field and examining the colour of thelatex exudation. Latex frommature storagerootsremainscreamywhite,while in imma-turestoragerootswhencut, the latexturnsblack.

Ininstanceswheretherearenoexternalvis-ible signs of maturity to indicate that har-vestingshouldtakeplace,growerswillhavetomonitor the development of the storagerootswithregularchecksofrootsizeafter18weeks.

Harvesting

Harvesting must be timely; if harvesting isdone tooearly yields canbe reduced.How-ever,ifthecropislefttoolongintheground,

Plate 23: White exudate from a mature sweet potato storage root

the storage roots can becomeprone to rot-tingandweevilattack.Traditionally,onsmallfarms,sweetpotatoisharvestedastheneedarises. However, this system of harvest ex-posesplantstoweevilattack.

Sweetpotatoesarenormallyharvested3-8monthsafterplanting,dependingonthecul-tivarandclimaticconditions.

Field operations

Sweetpotatoesareusuallyharvestedmanu-allywiththeuseofafork/cutlassormechani-callywithaharvester.Ahighlevelofdamagemayresultfrommechanicalharvesting.

Post production 5

34

31


35

• the time of the year the crop wasplanted(impactofdryandwetsea-son)

• the location inwhich the cropwasplanted(agro-ecologicalzone)

Currently yields in the Caribbean range be-tween 9 - 22 t/ha (8,000 - 20,000 lbs/ac).However, in several major producing coun-triesyieldsupto40t/ha(35,000lbs/ac)havebeenreported.

5.2 Post harvest handling

Thestoragerootsharvestedshouldbewashedin water using a sponge to remove all soilparticles;caremustbetakentominimisetheremoval of surface skin. This operation canbedonebyhandorbyaspecialisedwashingmachine.Toavoidspoilage,thewashingwa-tershouldcontain15ccper4.5 l (160floz/gal)ofcommercialbleach.Thewatershould

♦ Manual method

Thevinesarecutandafork/cutlassorother appropriate lifting tool shouldbeplacedmorethan30cm(1ft)awayfromwherethevineisattachedtothestorage roots. The roots are exposedbyturningthesoil.Thevinesmaynotseparate easily and individual rootshavetobedetachedbyhand.

♦ Mechanical method

The sweet potato ridges are clearedofvinestoallowtheharvestertohaveeasy access (Plate 24). The harvestermovesslowlythroughthefieldandthesweetpotatoesarebroughttothesur-facealongtheridge(Plate25).

Theskinofthesweetpotatoisthinanddeli-cateandeasilydamagedatharvest.Storageroots should therefore be handled carefullyand sparingly. The harvested crop, whetherbyhandormechanicallyshouldbeplacedinfieldcratestobetransportedfromthefield.Donotusesacksasthiscanresultinrubbingoff the surface skinand thebuild-upofdis-ease organisms. Sweet potatoes should begradedinthefield.

Yields

Theyieldsobtainedfromasweetpotatocroparedependentonthefollowing:

• whetherthecropwasrainfedorir-rigated

• varietyselectedPlate 24: Sweet potato vines cleared from the

ridges in preparation for the harvester (manual)

35


36

Plate 25: Harvester up-rooting the sweet potatoes (mechanical)

Plate 26: Storage roots exposed for selection

Plate 27: Exposed storage roots

Plate 28: Harvested crop (manual) be-ing placed in field crates to be trans-

ported from the field

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continuedduetoconsumerhealthconcernsrelatedtochemicalresidues.

Storage

Rottingofsweetpotatoesinstorageisclose-ly related to injury during harvest and sub-sequenthandling. Thiscanbepreventedbypromptcuring,carefulhandlinganddiscard-ing infectedrootsbeforestorage.Themajorpathogens causing rot are:Ceratocystis fim-briata, Fusariumspp.,Rhizopusspp.,Botryo-diplodia theobromaeandSclerotia rolfsii.

Packaging

Sweet potatoes should be packed in twopiece full telescopic fibreboard cartons (ba-nana type) holding 18 kg (40 lbs). Allow forweight loss of about 4% when shipping bysea. Cartons should be properly labeled toinclude the crop name (sweet potato), netweight aswell as the importer and suppliernames.

Transportation

Sweetpotatoescanbetransportedbyairorbyseaforupto14days inrefrigeratedcon-tainers. During sea shipment, the requiredstoragetemperaturesare12-13°C(54-55°F). Storage below these temperatures in-duceschillinginjury.Higherstoragetempera-tureswillresultinincreaseddecay,waterlossandsprouting.

bechangedwhenitlooksdirtyorafterevery500kgs (1,100 lbs)of sweetpotatoes.Onceclean,harvestedrootsshouldbedippedinasolutionMertec®20S(500ppmofTBZactiveingredient)beforebeinglefttodryovernight.The storage roots should be placed in fieldcrates and held at ambient temperature for3-5daystoallowrootcuringbeforefinalse-lection,packingandshipment(Plate28).

Grading

Sweetpotatoesaregradedaccordingtosizewith200g(8oz)beingtheminimumweightfor acceptance. Storage roots may also begradedaccordingtoshape.

Grades

Large:>800g(28oz)

Medium:450-800g(16-28oz)

Small:200-450g(8-16oz)

Postharvesttreatments

Curing

Aperiodofwoundhealingorcuringisrecom-mended toprevent fungal infectionofdam-agedroots.Optimalconditionsforcuringarebetween26-29°C(80-85°F)and85-90%relativehumidityfor4-7days.Thisformsacorkyperidermlayerbelowthedamagedar-easwhichlimitsmicrobialinvasionandwaterloss.

Fungicidal dips

The use of fungicides in the post harvesttreatment of sweet potatoes has been dis-

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IntheCaribbean,therehasandcontinuestobe a growing awareness of the health ben-efits of sweet potato. Research across theglobe has shown that sweet potato has at-tributes that can assist in managing manylifestyle diseases. Antidiabetic, antihyper-sensitive,anti-inflammatory(asthma,arthri-tis),antimicrobialandantioxidantpropertieshavebeenassociatedwiththecrop.Diversi-fyingtherangeofproductsavailabletocon-sumers isan importantaspectofpromotingtheconsumptionofthis importantfoodanddevelopingandsustainingtheindustry.

6.1 Nutritional content

In addition to containing simple starches,sweetpotatoesarerichincomplexcarbohy-drates,dietaryfibre,vitaminsA,CandB6aswell as manganese, copper, potassium andiron.WhencomparedtoIrishpotato,sweet-atorankshigherinnutritionalvalueandhassimilarcalories(Table3).

Sweet potato varieties range in flesh colourfromwhite, cream, yellow, orange and pur-ple. Orange flesh varieties have higher lev-elsof beta carotene than thosewith lightercolouredflesh.Purplefleshedvarietieshavehigher antioxidant properties. In the Carib-bean the predominant varieties are white,cream and yellowwith growing amounts oforangefleshedvarieties.

Source:HoldipJ,2006.CajanusTheCaribbeanFoodandNutri-tionInstitute,Quarterly

6.2 Value addition

Woldwide

A wide range of processed products canbe produced from sweet potato, includingsnacks, starch, confectionaries, condimentsand drinks. In Japan, the sweet potato pro-

6 Sweet potato nutrition, uses and value addition

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Table 3: Nutrient profile: sweet vs Irish potato

Nutrient Sweet potato Irish potato

Energy 90.00 93.00

Protein(g) 2.01 1.96

TotalFat(g) 0.15 0.10

Carbohydrate(g) 20.71 21.55

Fibre(g) 3.30 1.50

Calcium(mg) 38.00 5.00

Iron(mg) 0.69 0.35

Potassium(mg) 475.00 391.00

VitaminC(mg) 19.60 12.80

Niacin(mg) 1.49 1.40

Folate(mcg) 6.00 9.00

VitaminA(IU) 192.18 0.00

VitaminE(mg) 0.71 0.04


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Plate 29: Sweet potato products manufac-tured in Japan (flour, juices, alcohol, candy)

cessingindustryiswelldevelopedwithmanycommercialproductsavailableonthemarket.Insomecasestheseareretailed inspecialtysweetpotatostores.Productsmadefromthecrop in Japan includenoodles, jamsand jel-lies, sauces, flour, juices, wines, ice cream,alcoholandindustrialstarch.

Caribbean

TraditionallywithintheRegion,sweetpotatois consumed primarily boiled or baked andeatenasasidedish.Asconsumerstransitionfrom imported grains and cereals and con-sumemoretraditionalstaplesforhealthand

wellness reasons, there isagrowingmarketfor more “easy to prepare” forms of sweetpotato. Such foods range from minimallyprocessed (peeled, cut and blanched) tocompletely processed forms (flour, cereals,snacks,puddingmixes).

Thedevelopmentoflocalvalueaddedprod-ucts requires information on the chemical/

nutritional properties of local popular linessothattheproductsforwhichtheyarebestsuited can be identified. Among the institu-tions that have been working in this areaare the Barbados Agricultural DevelopmentandMarketingCorporation,NorthernCarib-beanUniversity(Jamaica),ScientificResearchCouncil (Jamaica), the Trinidad and TobagoAgri-business Association, The University oftheWestIndiesandCARDI.

Under a CARICOM/JAPAN bilateral proj-ect, CARDI, collaborated with the NationalResearch Council for Kyushu and Okinawa

Plate 30: Products made by the Food Tech-nology Department of the Scientific Research

Council (SRC), Jamaica

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(KONARC) of Japan to evaluate several Ca-ribbeanvarietiesfortheirsuitabilityforpro-cessing.Thirty-fourvarietieswereevaluated,fromJamaica,StVincentandtheGrenadines,StKittsandNevis,StLuciaaswellasTrinidadandTobago.Parametersexaminedwerebrix,and dry matter content. The results identi-

fiedthevarietiesthatweresuitableforeitherjuice,flour,pasteorfries(Table4).

Effortsarebeingmadetoidentifyadditionalvarieties within and outside of the Regionthat will assist in expanding the range ofproductsavailableforCaribbeanconsumers.

Flour

Paste

Juice

Fry

Centennial(TT)

SampsonLover’sName(SVG)

Audian’sLover’sName(SVG)

CARDILover’sName(SVG)

Clarke(SKN)

Thetford(JAM)

86BM-15(BDS)

CBS49(BDS)

Centennial(TT)

Carrot(TT)

Centennial(TT)

86BM-15(BDS)

CBS49(BDS)

CarolineLee(BDS)

ChickenFoot(TT)

SLU#1(SLU)

Mandela(SLU)

BlueBud(JAM)

Eustace(JAM)

UpLifter(JAM)

CarolineLee(BDS)

UpLifter(JAM)

WilliamWhite(SVG)

RedMan(BDS)

C104(BDS)

St.VincentUnknown(TT)

SLU#1(SLU)

Value added product

Sweet potato varieties

Orange flesh Yellow flesh

Table 4: Varietal suitability for value-added products

BDS–Barbados,JAM–Jamaica,TT–TrinidadandTobago,SKN-St.KittsandNevis,SLU–StLucia,SVG-St.VincentandtheGrenadines

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With the effects of global climate changeand the increasingoccurrenceofnaturaldi-sasters,farmersmustbeawareofandadoptpreventative measures to minimise the im-pactofthesedisastersontheiroperations.IntheCaribbean, thenaturaldisasters impact-ing cropproduction systems are hurricanes,floods,droughts, volcanicashandacid rain.If unprepared, these events canprove cata-strophictofoodsupply.

Of all the cultivated root and tuber crops,sweet potato is probably the best at adapt-ingquickly tonewconditions.Nevertheless,itsgrowthanddevelopmentcanbeaffectedby adverse environmental conditions. Dueto the unpredictability of natural disasters,sweetpotato farmers should takepreventa-tive measures to reduce their impact. Suchmeasures implementedmust take into con-sideration the features of the planting siteandthecrop.

Planningisoneofthemostimportantaspectsofmitigation as it can help tominimise theimpactofdisastersandalsohelpthefarmerto recover. Inaddition tomeasuresdirectedto specificdisasters, therearegeneralprac-ticesthatshouldbeundertakenregardlessofthenatureofthedisaster.

7.1 General practices

• Develop a farm plan indicating areaswhich have the potential for flooding,

drying, slippage and wind damage. Es-sentialinformationtorecordinclude:soiltype,slopeofthelandandwinddirection

• Plant hedgerows to shelter areas whicharepronetoextremewinds

• Clear farm refuse and other debris thatsurround fields; suchmaterialsmay clogdrainsand increase the chanceof flood-ing

• Establishphysical(plant,non-plant)rowsandbarriers or a cover crop to hold thesoil in areaswhich are prone to erosioncausedbywindand/orrain

• Have an idea of weather patterns/sea-sons; determine dry periods, those ofheavyrainandhurricanemonths

• Withconsiderationofthemarket,wherepossibleadjustplantingtimessothatpro-duction isconductedduringseasons lesspronetoextremeweatherconditions

• If planting is occurring during disasterprone seasons, plant varieties of sweetpotato that mature quickly. In droughttimesusevarieties thataredeep rootedand reduce the chances of pest infesta-tionofstorageroots

7 Disaster mitigation and adaptation

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Volcanicashandacidrain

Although not widespread, volcanic ash fallandacid rainwhich results froman interac-tionbetweenrainfallandvolcanicgasareofconcern for some locationse.g.Montserrat.Apossiblemeasure to reduce the impactofash and acid rain is to grow the cropundera partial or fully covered structure. Struc-turescanberowcovers,shadeand/orhoophouses.Carehastobetakenthatthecover-ingusedprovides the right amountof light.Therefore, the structure has to be cleanedregularly. In addition the structuremust beabletowithstandtheweightofthevolcanicash.Sweetpotatohasbeengrownunderpro-tected systemswith yields achieved compa-rabletoopenfield.

7.2 Practices for specific disasters

Hurricanesandflooding

• Establishthecroponraisedbedssoastoincreasedrainageandreduceerosion

• Cutdrainsinfloodproneareasofthefieldtoreducetheimpactofwaterlogging

• Secure and store planting material thatcouldbeusedtore-establishacrop.Thiscouldbethroughharvestingvinesand/orsmallpotatoeswhicharesproutedwhenneeded

• Oncethefieldhasbeendrained,applyafungicidetopreventtheimpactofpatho-gens

Droughts

• Irrigate the field; a drip systemwill pro-videthemostefficientwateruse

• Useplasticmulchtocoverbedsandcon-serve soil moisture. Grass mulch couldalsobeused,butcarehastoensurethatthemulchdoesnotharbourpests

• Mold plants to reduce soil cracks thatprovideentryofpeststotherootzone

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Recordkeeping

Record keeping is the process of collectingdataon all factors thatmay impact on cropproduction, post-harvest and marketing ac-tivities.Accurate recordsallowproducers tohaveaclearunderstandingofthefactorsthatinfluenceproductivityandothercostsandassuch,insightsastoprofitabilityoftheopera-tion.

Cost of production

Costofproductioncalculationsareimportantas they allow farmers to assess their profitmargins.Table5givesanexampleofthetypeofdatawhichhastobecollectedforaccuratecostofproductioncalculations.

Record keeping 8Expenditure (variable costs)

Table 5: An example of the information required to calculate the cost of production

Crop establishment Land preparationLandclearing(mandays)Ridging(mandays)Forking(mandays)TractorservicesLimestone(kg)/Liming(mandays)Other(establishingirrigationsystem(mandays),soiltest)Planting materialSlips/cuttingsperhectareCrop care Agro-chemical inputs and other materials and suppliersFertiliser(50kgbag)Fungicides(packets/bottles)Insecticide(packets/bottles)Herbicide(packets/bottles)Other(packets/bottles)


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Table 5: Example of the information required to calculate the cost of production (continued)

Crop care (continued)Agro-chemical inputs and other materials and suppliersPheromoneandtrapsFuelformaintainingfarmequipment(e.g.,weedwacker)OtherMaintenance labourPlanting(mandays)Fertilising(mandays)PesticideapplicationsWeeding(manual-mandays)HarvestingHarvesting(manual-mandays)Harvesting(mechanical-harvester)TransportfromfieldtomarketOverhead expense (e.g., % of total cost)LandleaseSpraycansTractorIrrigationsystemOther

Totalharvestedyield(kg/ha)Marketableyield(kg/ha)Sweetpotatoplants(slips/ha)Yieldperplant(kg/plant)Averageprice(perkg)

Returns


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48 CTAThis document has been produced with the financial assistance of CTA. The views expressed herein are those of CARDI and can therefore in no way be taken to reflect the official opinion of CTA.

HEADQUARTERS CONTACT INFORMATION

Email: [email protected]: www.cardi.orgFax: 1-868-645-1208Tel:1-868-645-1205/8120

P.O. Bag 212University of the West IndiesSt. Augustine Campus, St. AugustineTrinidad and Tobago

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