ArticlePDF Available

Non-chemical weed management in vegetables by using cover crops: A review

Authors:

Abstract and Figures

Vegetables are a substantial part of our lives and possess great commercial and nutritional value. Weeds not only decrease vegetable yield but also reduce their quality. Non-chemical weed control is important both for the organic production of vegetables and achieving ecologically sustainable weed management. Estimates have shown that the yield of vegetables may be decreased by 45%-95% in the case of weed-vegetable competition. Non-chemical weed control in vegetables is desired for several reasons. For example, there are greater chances of contamination of vegetables by herbicide residue compared to cereals or pulse crops. Non-chemical weed control in vegetables is also needed due to environmental pollution, the evolution of herbicide resistance in weeds and a strong desire for organic vegetable cultivation. Although there are several ways to control weeds without the use of herbicides, cover crops are an attractive choice because these have a number of additional benefits (such as soil and water conservation) along with the provision of satisfactory and sustainable weed control. Several cover crops are available that may provide excellent weed control in vegetable production systems. Cover crops such as rye, vetch, or Brassicaceae plants can suppress weeds in rotations, including vegetables crops such as tomato, cabbage, or pumpkin. Growers should also consider the negative effects of using cover crops for weed control, such as the negative allelopathic effects of some cover crop residues on the main vegetable crop.
Content may be subject to copyright.
Agronomy2020,10,257;doi:10.3390/agronomy10020257www.mdpi.com/journal/agronomy
Review
NonChemicalWeedManagementinVegetablesby
UsingCoverCrops:AReview
HusrevMennan
1,
*,KhawarJabran
2
,BernardH.Zandstra
3
andFiratPala
4
1
DepartmentofPlantProtection,AgricultureFaculty,OndokuzMayisUniversity,55139Samsun,Turkey
2
DepartmentofPlantProductionandTechnology,FacultyofAgriculturalScienceandTechnologies,Nigde
OmerHalisdemirUniversity,51240Nigde,Turkey;khawarjabran@gmail.com
3
DepartmentofHorticulture,MichiganStateUniversity,EastLansing,MI48824,USA;zandstra@msu.edu
4
DepartmentofPlantProtection,AgricultureFacultySiirtUniversity,
56100Siirt,Turkey;
firatpala@gmail.com
*Correspondence:hmennan@omu.edu.tr;Tel.:+903623121919
Received:04December2019;Accepted:05February2020;Published:11February2020
Abstract:Vegetablesareasubstantialpartofourlivesandpossessgreatcommercialand
nutritionalvalue.Weedsnotonlydecreasevegetableyieldbutalsoreducetheirquality.
Nonchemicalweedcontrolisimportantbothfortheorganicproductionofvegetablesand
achievingecologicallysustainableweedmanagement.Estimateshaveshownthattheyieldof
vegetablesmaybedecreasedby45%–95%inthecaseofweed–vegetablecompetition.
Nonchemicalweedcontrolinvegetablesisdesiredforseveralreasons.Forexample,thereare
greaterchancesofcontaminationofvegetablesbyherbicideresiduecomparedtocerealsorpulse
crops.Nonchemicalweedcontrolinvegetablesisalsoneededduetoenvironmentalpollution,the
evolutionofherbicideresistanceinweedsandastrongdesirefororganicvegetablecultivation.
Althoughthereareseveralwaystocontrolweedswithouttheuseofherbicides,covercropsarean
attractivechoicebecausethesehaveanumberofadditionalbenefits(suchassoilandwater
conservation)alongwiththeprovisionofsatisfactoryandsustainableweedcontrol.Severalcover
cropsareavailablethatmayprovideexcellentweedcontrolinvegetableproductionsystems.
Covercropssuchasrye,vetch,orBrassicaceaeplantscansuppressweedsinrotations,including
vegetablescropssuchastomato,cabbage,orpumpkin.Growersshouldalsoconsiderthenegative
effectsofusingcovercropsforweedcontrol,suchasthenegativeallelopathiceffectsofsomecover
cropresiduesonthemainvegetablecrop.
Keywords:covercrops;weeds;vegetables;nonchemicalweedcontrol;allelopathy;physicalweed
control
1.Introduction
Severalproductionproblemsdiminishthequalityandyieldofvegetables.Salinity,drought
stressandclimatechangesareafewabioticfactorsthatdecreasetheyieldofvegetableswhilethe
majorbioticfactorsthatreducetheyieldincludediseasepathogens,insectpests,viruses,andweeds[1].
Theyieldlossescausedbyuncheckedweedsinvegetableproductionsystemsmaybebetween45to
95%dependingontheproductionenvironment[2].Despitethecommonuseofherbicidesinthe
USA,thelossinvalueofcertainvegetablesduetoweedsrangedbetween8%to13%[3].Weedsnot
onlyreducetheyieldofvegetablesbutalsodecreasetheirqualityandmarketvalue[4].
Chemicalweedcontrolhasbeenagreatoptioninconventionalvegetableproductionsystems
becauseitprovideseffectiveandsustainableweedcontrol.However,overuseofherbicidescauses
environmentalconcernsbecauseherbicideshavenegativeeffectsonnontargetorganisms
Agronomy2020,10,2572of16
(beneficialspecies),maypollutethefoodandgroundwaterwiththeirresidue,andcausetoxicityin
mammalians[5,6].Therehasbeenagreaterinterestinnonchemicalweedcontrolafterpeople
becamemoreawareofthedamagecausedbythemisuseofherbicides[7].
Weedsineitherorganicorconventionalvegetableproductionsystemscanbecontrolled
throughhandhoeingormechanicalcultivation.Interrowcultivationhasaprovenusefulnessfor
controllingweedsinvegetableproductionsystemsbutthehighcostoffuelmayconstrainthis
practice.Moreover,thepracticeofinterrowcultivationmayacceleratesoilerosion[8–10].
Programmedweedcontrollingrobotshavepotentialfortheautomationofweedmanagement
operations.However,becausethetechnologyisexpensive,itstillneedssometimetobeadoptedby
thevegetablegrowers.Therootsystemofvegetablesmaybedamagedbythehandhoeing,andthis
practiceislaborintensiveandcostly[7,11,12].
Organicandconventionalvegetableproductionsneedeffectiveweedcontrolstrategies.Theuse
ofcovercropsforallelopathicandphysicalweedcontrolisamongtheeffectivestrategies[13–16].
Covercropscanbeconsideredaseffectivetoolstosuppressweedsinvegetablefields[14,17].Cover
cropscanactasanalternativetotillageforcontrollingweedsandreducingyieldlossescausedby
weeds[18].Covercropsarenotgrownasacashcropbutratheraregrownforseveraloftheir
ecologicalbenefits.Someofthesynonymsusedforcovercropsarelivingmulch,catchcrop,smother
cropandgreenmanure.Thesecanbegrownduringfallowperiods,alongwiththemaincashcropor
duringapartofthegrowingseasonofacashcrop.Theecologicalbenefitsofcovercropsarenot
limitedtoimprovementsinsoilfertility,soilconservationorpestsuppression.Covercropsmodify
themicroclimateofthecompanioncropbyinterceptingsunradiation,provideahabitatfor
beneficialbiologicalagents,suchasinsectsthatpreyonweedsorotherdetrimentalinsects,modify
theenergyofraindropsandplayaroleintheuniformdistributionofprecipitationinthesoil.
Besidesthosefeatures,covercropsmaydecreaseerosion,conservesoilmoisture,increasesoil
fertilityandimproveitsstructure.Negatively,sometimescovercropsmayalsofacilitate/promote
somepestsand,ifnotremovedpriortothecriticalperiodforweedcontrolofthecompanioncrop,
canthemselvesactasweedsandreducecropyield[19].
Previousresearchshowsthatcovercropscanbegrownforweedcontrolinvariousagricultural
systems[20–22].Manycovercropshavebeeninvestigatedindifferentpartsoftheworldandhave
showngoodresults.Forexample,covercropssuchasfodderradish(RaphanussativusL.),vetch
(Viciaspp.),rye(SecalecerealeL.)ortheirappropriatecombinationscanprovideeffectiveweed
controlinnotillorganiccropproductionsystems[23].S.cerealewithallelopathicpotential
decreasedthebarnyardgrass(Echinochloacrusgalli(L.)P.Beauv.)leafcountanddrybiomass[24].A
numberofreviewarticlesareavailablethataddressvariousaspectsofcovercrops.Nevertheless,to
thebestofourknowledge,noreviewarticleaddressestheuseofcovercropsforachieving
nonchemicalweedcontrolinvegetablecrops.Hence,inthisreviewpaper,wehavereviewedthe
literaturetoexplaintheyieldlossescausedbyweedsinthevegetables,theneedfornonchemical
weedcontrolinvegetables,theuseofcovercropsforweedcontrolinvegetablesandthe
disadvantagesofthecovercrops.
2.YieldLossesCausedbyWeedsinVegetableCrops
Weedsareasignificantissueintheproductionofvegetables.Severalfactorsaffectthedegreeof
vegetableyieldreductionanddamagetoqualitycausedbyweeds.Themostimportantoftheseare
thecompetitivenessofthevegetableplantswiththeinfestingweeds,therelativedensitiesofweeds
andvegetableplants,weedemergencetime,andthecompetitionduration[25–27].Vegetables
plantedeitherasseedsorseedlingsareweakcompetitorsbecauseoftheirshallowrootsystemand
sluggishgrowth,especiallyduringtheearlystages.Hence,thevegetablesarehighlysensitiveto
weedcompetitionandneedtobekeptweedfreeduringthatearlygrowthstage.Theyieldlosses
causedbyweedsinvariousvegetableshavebeenreportedinpreviousstudies.Forexample,weed
coverinpea(PisumsativumL.)was73%ifitwasgrownwithoutanycovercrop,i.e.,withoutany
weedcontrolpractice[28].Decreaseinyieldoflettuce(LactucasativaL.)becauseofweed
competitionhasbeenreportedinpreviousstudies[29].InastudyfromEngland,adensityof65
Agronomy2020,10,2573of16
weedsm2,includingamixtureofbroadleafandnarrowleavedweeds,couldcompletelydestroythe
lettucecrop[29].Similarly,astudyfromCaliforniashowedthatlettuce–weedcompetitionforthe
wholegrowingseasondecreasedtheyieldby50%[30].InFlorida,aseasonlonglettuce–weed
competitionreducedtheyieldoflettuceby56%[31].Besidestheyieldreduction,thequalityof
lettuceisalsoreducedduetoweedcompetition[32].Similarly,weedcompetitioninsoybean
(Glycinemax(L.)Merr.)duringthefirst(v1)andthirdfoliates(v3)stages(accordingtoBBCH)was
criticalindamagingthecropplantdevelopment[33].
Similarly,inpepper(CapsicumannuumL.),weedssuchaspurplenutsedge(CyperusrotundusL.)
coulddecreasethefruityieldbyupto44%[34].Inanotherstudy,thefruitnumberofthebellpepper
(C.annum)wasdecreasedby94%ifitsgrowthwasinterferedwithbytheweedPalmeramaranth
(Amaranthuspalmeri(S.)Wats.)[16].Moreover,aweedfreeperiodof12.2weekswasneededbychili
pepper(C.annum)toavoidayielddecreaseofmorethan5%[35].Yieldofthetomato(Solanum
lycopersicumL.)wasdecreasedby48%–71%whenthevegetableplantsweregrowingincompetition
withweedssuchaslargecrabgrass(Digitariasanguinalis(L.)Scop.),tallmorningglory(Ipomoea
purpurea(L.)Roth),commoncocklebur(XanthiumstrumariumL.),andjimsonweed(Datura
stramoniumL.)[36].
3.NeedforNonChemicalWeedControlintheVegetableCrops
Nonchemicalweedcontrolisdesiredforseveralreasons.Thedevelopmentofmodern
vegetableproductionsystemsislikelytobeslowedifweedmanagementoptionsarelimited[37].
Theavailabilityofnonchemicalweedcontrolmethodsalongwithweedcontrolwithherbicideswill
increasethelikelihoodofachievingsustainableweedcontrolinvegetableproductionsystems.
Furthermore,thereisastrongdemandfororganicfoods,particularlyforvegetablesglobally,and
thisorganicvegetableproductionisnotpossiblewithoutnonchemicalweedcontrol[38].
Herbicideresistantweedsinvegetableproductionsystemsalsostresstheneedfor
nonchemicalweedcontrol[39].Similarly,themisuseofherbicidescausesenvironmentalpollution,
andnonchemicalweedcontrolshouldbeavailableasanadditionalchoiceforsustainableweed
control[7,40].
4.TypesofCoverCrops
Covercropscouldbeclassifiedintofourgroupsbasedontheirtaxonomy.Table1givesa
comprehensivelistofcovercropsthathavebeenusedforcontrollingweedsinvegetablesandother
crops,andforachievingotherecologicalbenefits.Accordingtothisclassification,therearegrasses,
legumes,Brassicaceaeplants,andothers.Importantexamplesofgrasscovercropsareryegrass
(LoliummultiflorumLam.),barley(HordeumvulgareL.),andsorghum(Sorghumspp.).R.sativusand
mustards(Sinapisspp.)areimportantintheBrassicaceaeplants.Similarly,beans(Phaseolusspp.),
vetches(Viciaspp.)andpeas(Pisumspp.)areimportantpulsesthataregrownascovercrops(Table1).
Growersmayselectafewofthesecovercropspecies,consideringtheirspecificfarmsituations.For
example,theymayavoidusinglegumesandprefercerealcovercropsifthesoilisrichinnitrogenor
hasnitrogenresiduefromthepreviouscrop.Ontheotherhand,legumecovercropsmaybe
preferredifthesoilhaslessnitrogen[41].
Table1.Alistofimportantcovercropsusedforweedcontrolandotherecologicaladvantages.
CoverCropTypeNameofCoverCropReference
Cereals
Bristleoat(Avenastrigosa)[42]
Winterrye(Secalecereale)[43]
Oat(Avenasativa)[43]
Sudangrass(Sorghum×sudanense)[44]
Wheat(Triticumaestivum)[44]
LegumesPea(Pisumsativum)[45]
Cowpea(Vignaunguiculata)[44]
Agronomy2020,10,2574of16
Subterraneanclover(Trifoliumsubterraneum)[45]
Crimsonclover(Trifoliumincarnatum)[45]
Egyptianclover(Trifoliumalexandrinum)[45]
Redclover(Trifoliumpratense)[45]
Sunnhemp(Crotalariajuncea)[45]
Velvetbean(Mucunapruriens)[45]
Soybean(Glycinemax)[45]
Fababean(Viciafaba)[45]
Hairyvetch(Viciavillosa)[43]
Commonvetch(Viciasativa)[46]
Brassicaceaeplant
Forageradish(Raphanussativus)[42]
Rapeseed,canola(Brassicanapus)[45]
Whitemustard(Sinapisalba)[45]
Nonlegumes
Buckwheat(Fagopyrumesculentum)[42]
Flax(Linumusitatissimum)[42]
Niger(Guizotiaabyssinica)[42]
5.HowCoverCropsSuppresstheWeeds?
Suppressionofweedsthroughcovercropsisdependentonseveralfactorsandaselectiveweed
controlisofferedbysomecovercrops[13,42–46].Therefore,cereal,legumeandbrassicaceaecover
cropsarewidelyusedinvariouscroppingsystems.
Weedsuppressionthroughcovercropsisachievedbymorethanasingleaction.Importantly,
bothcompetitionandallelopathyhavebeenassumedasmechanismsofweedsuppressionbycover
crops[46,47].Oneimportantmechanismofactionofacovercropisitsphysicaleffectonweeds.
Mostofthestudiesontheeffectsofcovercropsonweedsessentiallyconsiderthequantityof
accumulatedcovercropbiomass[48].Acovercropwithhighbiomassproductionislikelyto
produceagoodphysicaleffectonweeds,andhenceresultineffectiveweedsuppression.
Earlyseasontotalbiomassaccumulationbycovercropsreducestheriskofweedemergence
(Figures1and2)[49,50].ThegrasscovercropsL.multiflorum,A.sativa,andS.cerealehadahigher
biomassthantheothercovercropsandsuppressedtheweedseffectively(Figures3and4).
Figure1.Biomassproduction(kgha1)ofcerealcovercropsindifferentvegetableproduction
systemspriortoterminationin2005(graybars)and2006(whitebars).Verticallinesrepresent
standarderrorsofthemeans(p<0.05)[49,50].
0
500
1000
1500
2000
2500
3000
3500
4000
L.multiflorum A.sativa S.cereale S.bicolor T.aestivum S.vulgare
Biomass(kgha1)
Covercrops
Agronomy2020,10,2575of16
Figure2.Biomassproduction(kgha1)ofcovercropsindifferentvegetableproductionsystemsprior
toterminationin2005(graybars)and2006(whitebars).Verticallinesrepresentstandarderrorsof
themeans(p<0.05)[49,50].
Figure3.Effectsofvariouscerealcovercropsindifferentvegetableproductionsystemsonthedry
biomassproduction(gm2)ofweedspeciesatthetimeofcovercropterminationin2005(graybars)
and2006(whitebars).Verticallinesrepresentstandarderrorsofthemeans(p<0.05)[49,50].
0
500
1000
1500
2000
2500
3000
3500
4000
4500
P.sativum T.
meneghinianum
T.aestivum T.alexandrinum V.sativa V.villosa
Biomass(kgha1)
Covercrops
0
100
200
300
400
500
600
700
L.multiflorum A.sativa S.cereale S.bicolor T.aestivum S.vulgare Control
Weeddrybiomass(gm2)
Covercrops
0
100
200
300
400
500
600
700
P.sativum T.meneghinianum T.alexandrinum V.sativa V.villosa Control
Weeddrybiomass(gm2)
Covercrops
Agronomy2020,10,2576of16
Figure4.Effectsofvariouslegumecovercropsindifferentvegetableproductionsystemsonthedry
biomassproduction(gm2)ofweedspeciesatthetimeofcovercropterminationin2005(graybars)
and2006(whitebars).Verticallinesrepresentstandarderrorsofthemeans(p<0.05)[49,50].
ThebiomassesofL.multiflorum,A.sativa,andV.sativaspecieswererecordedashavingthe
highestvalues(Figure1).Ontheotherhand,thebiomassesaccumulatedbyP.sativum,S.bicolor,and
ballclover(TrifoliummeneghinianumClementi)specieswererecordedasthelowestvalues,
respectively.Covercropshadastrongerimpactonthebiomassofweedsthanontheirdensity.Even
ifweedswerefoundinahighnumberafteracovercrop,therewasagreaterdecreaseintheir
biomass[51].Sometimes,amixtureofcovercropsmayperformbetterthanasinglecrop,butthis
maynotalwaysbethecase.AcomparisonofS.cereale,hairyvetch(ViciavillosaRoth),andaS.
cerealeV.villosacombinationshowedthatS.cerealewasthebestweedsuppressorcovercropandthe
mixtureofS.cereale–vetchwassimilartotheS.cerealecovercrop[51].
Astatisticalrelationship(correlation)hasalsobeenconsistentlydescribedforthequantityof
covercropbiomassandtheextentofweedsuppression(Figures3and4).Acovercropbiomassof8t
ha1orhighermaybeenoughtoachieveasatisfactoryandsustainableweedsuppression[48].For
instance,forageradishisanimportantcovercropanditsweedsuppressingmechanismhasbeen
reportedpreviously[52].Rapidcanopydevelopmentandotherweedcompetitivetraitsofforage
radishwerefoundtobeacauseofweedsuppressionandallelopathywasfoundtohavenorole[52].
Generally,earlysoilcoverageandahighseedingrateofcovercropscanincreasepressureonweeds.
Growingacovercropwithahigherseedingdensitymeansproducingmorebiomassofcovercrop;
thiswillultimatelysuppressmoreweeds[53].S.cerealecovercropseedingratesdidnotaffectthe
weedemergence,butahighcovercropdrybiomassproducedahighseedingratethatdecreasedthe
weedbiomass[54].
Weeddrybiomassesbecauseoftheapplicationofcovercrops,includingP.sativum,T.
meneghinianum,andT.alexandrinumspecies,wererecordedashavingthehighestvaluesafterthe
valueofcontrolplots(Figures3and4).Ontheotherhand,thedrybiomassofL.multiflorum,S.
cerealeandT.aestivumspecieswererecordedashavingthelowestvalues,respectively.
Thedensityofweedsinsudangrass(Sorghumvulgare),S.bicolor,andT.aestivumwererecorded
ashavingthehighestvaluesafterthevalueofcontrolplots(Figure5).Ontheotherhand,theweed
densityofL.multiflorum,A.sativa,andS.cerealewererecordedashavingthelowestvalues,
respectively.
Figure5.Effectsofvariouscerealcovercropsindifferentvegetableproductionsystemsonweed
densityafterdifferenttimeofcovercroptermination.Verticallinesrepresentstandarderrorsofthe
means(p<0.05)[49,50].
0
5
10
15
20
25
14 28 56
Weeddensity(plantm2)
Daysafterterminationcovercrops(DAT)
L.multiflorum
A.sativa
S.cereale
T.aestivum
S.bicolor
S.vulgare
Control
aa
a
a
b
a
a
a
bb
c
c
bc
b
b
b
a
b
b
bc
b
a
a
Agronomy2020,10,2577of16
Severalothermechanismsexistthathelpthecovercropstosuppressweedsinvegetablecrops.
Forinstance,competitionforspacebetweenlivingcovercropsandweedsreducesthespacefor
weeds.Shadingistheothermechanismthroughwhichcovercropsarelikelytosuppressweedsin
vegetablecrops.Further,thecovercropsalterthelightqualitythatislikelytoinfluencethe
developmentofweeds[55].Forexample,farredlightreflectioncausesdevelopmentalchangesin
weedsthatreducestheirbiomassandseedproduction[56].Somecovercropsinducethe
germinationofweedseeds,andhencecauseadepletionoftheweedseedbank;e.g.,amixtureofS.
cereale,buckwheat(FagopyrumesculentumMoench),andyellowmustard(Brassicajuncea(L.)Czern.)
grownasacovercrophelpedtocompletelydepleteSetariaspp.intheweedseedbank,andcaused
an80%–85%decreaseinthegerminableseedbankofvelvetleaf(AbutilontheophrastiMedik.)and
commonlambsquarters(ChenopodiumalbumL.)[57].Thelongtermpracticingofcovercropping
resultsinareductionintheweedseedbankinthesoil[58].Earlieremergenceofacovercropmay
enableittocauseahighsuppressionofweeds[59].Theweeddrybiomassinorganicallygrown
vegetableswasinverselyproportionaltotheseedingratesoflegumes(e.g.,V.faba,P.sativum)and
cereal(A.sativa)[60].
Theallelopathicpotentialofcovercropsistheotherimportantmethodthroughwhichcover
cropssuppressweeds(Table2).S.cerealeisamongthemosteffectiveandimportantcovercropsand
itsallelopathicpotentialhasbeenreportedconsistentlyintheliterature[61–63].S.cerealevariesin
theconcentrationofallelochemicalsand,hence,theeffectonweeds.Thecultivarsvariedintheir
contentofbenzoxazinoides,whileweedshadavariableuptakeofallelochemicalsthatcausedsome
weedstobemoresensitivetocovercrops.Forexample,ingreenhouseandfieldexperiments,
redrootpigweed(AmaranthusretroflexusL.)andcommonpurslane(PortulacaoleraceaeL.)showeda
greaterresponsetoS.cerealecovermulchesthanC.album[64].AllelochemicalssuchasDIBOA,BOA,
DIBOAglucoside,andAZOBhavebeenreportedfromS.cerealeplants,andthepersistenceofthese
allelochemicalsinthesoilhadacorrelationwiththeaccomplishedlevelofweedcontrol[47,65,66].
PlantsfromtheBrassicaceaefamilyareanimportantcovercropgroupforweedsuppression.
Glucosinolatesareimportantallelochemicalsthatarepresentinbrassicaspeciesandmayhavearole
intheweedcontrolactivity[67].Brassicacovercropsexudetheseglucosinolatestothesoil
environment,wheretheyareconvertedtotheiractiveform,i.e.,isothiocyanates.Forinstance,six
allelochemicals(isothiocyanates)wereidentifiedinfieldmustard(BrassicarapaL.);thesewere
2phenylethylITC,nbutyl,3butenyl,benzyl,allyl,and4pentanyl[68].Previousstudieshave
describedtheallelopathiceffectsofcovercropsonweeds.WeedssuchasC.albumandwildfoxtail
millet(Setariamedia(L.)Vill.)weresuppressedby60%bycovercropssuchaswhitemustard(Sinapis
alba),R.sativus,V.sativaandthemixtureofthesecovercropssuppressedtheweedsby66%[69].In
manyinstances,itmaybedifficulttoquantifytheexactmechanismofweedsuppressionbycover
crops.Insuchcases,bothcompetitionandallelopathy,oranyofthese,maybeinvolved.For
example,thecovercropsdecreasetheemergenceofweedseedlings,expansionoftheweedcanopy
andbiomassproductionbyweeds,andthiswasachievedeitherthroughphysicaleffector
allelopathy[70].
Table2.Allelochemicalsreportedinvariouscovercrops.
CoverCropAllelochemicalsReference
Rye(Secale
cereale)MBOA,BOA,HMBOA,DIBOA[71]
Barley(Hordeum
vulgare)
Gramine,hordenine,phydroxybenzoicacid,vanillicacid,
pcoumaricacid,syringicacid,ferulicacid[72,73]
Sorghum
(Sorghumbicolor)Sorgoleone,mcoumaricacid,caffeicacid,chlorogenicacid[74]
Wheat(Triticum
aestivum)
DIMBOA,2,4Dihydroxy1,4benzoxazine3one(DIBOA)[75]
DIMBOA,syringicacid,vanillicacid,phydroxybenzoicacid,
cisferulicacid,transferulicacid,transpcoumaricacid,
cispcoumaricacid
[76]
Agronomy2020,10,2578of16
Fieldmustard
(Brassicarapa)2Phenylethylisothiocyanate[67]
Rapeseed
(Brassicanapus)
Glucosinolates,2Phenylethylisothiocyanate,benzyl
isothiocyanate,allylisothiocyanate,3butenylisothiocyanate,[77,78]
Fieldmustard
(Brassica
campestris)
Benzylisothiocyanate,allylisothiocyanate,3butenyl
isothiocyanate[78]
Thereisparticularsignificanceinusingcovercropsforweedcontrolinnotillsystems.In
conventionalvegetableproductionsystems,theweedsarecontrolledbyusingtillageasatoolalong
withotherweedcontrolmethods,suchasherbicideapplications.However,notillvegetable
productionhasbeenpopularinrecentyearsduetoassociatedbenefitssuchasenvironmentaland
resourceconservation,andcosteffectiveness.Growingvegetablesinthenotillsystemlimitsthe
weedcontroloptionsasitrestrictstheuseoftillage,whichisapracticeprimarilycarriedoutfor
seedbedpreparationandweedcontrol.Covercropsareanexcellentoptiontocontrolweedsin
notillvegetablesystems.Covercropsalsoconservethesoilandwaterandpromoteahealthy
environmentforsustainablevegetableproduction.
Anotherimportantquestionthatarisesintheuseofcovercropsisthepersistenceofallelopathic
substancesinsoilandaccordingactivitylevels.Soilfactorscanmodifytheallelopathicactivityof
covercropsinthesoil;themostimportantofthesefactorsaretheionexchangecapacityofthesoil,
theconcentrationoforganicmatterinitandthebioticcontent[79].Forexample,phenolicacid
concentrationsmayreachamaximumafter10–15daysofcovercropincorporationsandmayremain
effectiveuntil20–25days[80].Thiscovercropresidueinhibitsthegerminationofweedseedsand
decreasestheweeddensity,buttheireffectsareactiveforashorttimeandtheweedsoftenreemerge
[81].
Table3.Covercropswithanallelopathicpotentialandtheweedssuppressedbycovercrops.
CoverCropWeedsSuppressedReferences
Wheat(Triticumaestivum)Ipomoealacunose,Eleusineindica
,
Amaranthuspalmeri[82]
Rye(Secalecereale)Eleusineindica
,
Amaranthuspalmeri
,
Ipomoealacunosa[82]
Rye(Secalecereale)Chenopodiumalbum
,
Abutilontheophrasti[83]
Annualryegrass(Loliummultiflorum),
rye(Secalecereale),bristleoat(Avena
strigosa),commonvetch(Viciasativa),
radish
Brachiariaplantaginea,Bidenspilosa,
Euphorbiaheterophylla[23]
Hairyvetch(Viciavillosa),oat(Avena
sativa)
Digitariasanguinalis
,
Eleusineindica
,
Amaranthusretroflexus,Datura
stramonium
[84]
Sorghumsudangrass(Sorghum
bicolor×Sorghumsudanense)Broadleavedweeds[85]
Bristleoat(Avenastrigosa)
hairy
vetch(Viciavillosa)
Amaranthuspalmeri
,
Portulacaoleracea
,
Helianthusannuus[86]
Rye(Secalecereale),hairyvetch(Vicia
villosa),barley(H.vulgare)×triticale,
Austrianwinterpea(Pisumsativum)
Chenopodiumalbum
,
Amaranthushybridus
,
Thlaspiarvense,Taraxacumofficinale,
Stellariamedia,Elymusrepens,Panicum
crusgalli,Setariaglauca
[87]
Whitemustard(Sinapisalba)Amaranthusblitoides,Chenopodiumalbum[88]
Agronomy2020,10,2579of16
Hairyvetch(Viciavillosa)
,
subterraneanclover(Trifolium
subterraneum),oat(Avenasativa)/hairy
vetch(Viciavillosa)
Amaranthusretroflexus,Chenopodium
album[89,90]
6.DisadvantagesofUsingCoverCropsforWeedControlinVegetableProductionSystems
Althoughcovercropscanrepressweedsandhaveadditionalecosystembenefits,somenegative
aspectsofusingcovercropsinvegetableproductionsystemshavealsobeennoted.Forexample,
someofthecovercropsmaypromotesomeinsectpestsordiseasepathogens[91].Moreover,as
vegetableshaveadifferentmorphologyandgrowthhabittootherarablecrops,therearechances
thatcovercrops,alongwithweeds,mayalsocompetewithvegetablecrops.Hence,acareful
managementplanisrequiredwhencovercropsaretobeusedforweedcontrolinvegetables[92].
Covercropsmaynotalwaysprovideeffectivecontrolofweedsinvegetables,i.e.,negativeor
noeffectsofcovercropsinvegetableshavealsobeennoted.Forexample,foragesoybeanwasused
asacovercropincollard(BrassicaoleraceaL.)vegetables;thecovercropwasineffectiveincontrolling
weeds[93].Moreover,covercropsmayoccasionallyhaveapositiveeffectongerminationor
seedlinggrowthofweeds[94].Additionally,someshortfallsofcovercropsasaweedcontrol
techniquearealsoonrecord.Forexample,covercropsmaynotbeeffectiveincontrollingintrarow
weeds;thisisbecauseneithertheirallelopathiceffectsnorshadingeffectreachestheintrarows.This
mayalsobethereasonthatcovercropsusuallydamageonlytheweedsandnotthecrops[95,96].
Throughtheuseofcovercropsinvegetables,annualweedsareeasilycontrolled,butperennials
generallyreceivealowerimpactwhilesedgesaredifficulttocontrol[97].Otherresearchworkalso
showedthatcovercropsmayhaveweakeffectivenessagainstperennialweedssuchasnutsedges
(Cyperusspp.)[47,58]
Anotherimportantaspectisthathighbiomassproduction(inordertogaingreaterweed
suppression)maydisturbtheseedingoperation,cropestablishmentandothercropmanagement
operations[98].Similarly,allelochemicalsfromcovercropscanposeanegativeeffectonthemain
vegetablesalongwiththeireffectsonweeds[64].Awellestablishedpracticeistogrowcovercrops
andthendesiccatethesethroughsomemeans(e.g.,herbicideapplication,mechanical
incorporation).Theresiduecovercropsuppressestheweedsinthenextseasoncrop;however,there
isalikelinessthatthiscovercropresiduewillalsonegativelyaffectthegerminationandseedling
growthofthemaincrop.Forexample,thegermination,seedlingemergenceorestablishmentof
spinach(SpinaciaoleraceaL.)andlettucewerenegativelyaffectedbytheallelopathicactivityoftwo
importantcovercrops,S.cerealeandwinteroilseedrape(BrassicanapusL.)[94]
7.CoverCropsforWeedControlinVegetableCrops
Covercropsarenowcommonlyusedinorganicvegetableproductionsystemsinsomepartsof
theworld[97].Forexample,growinglegumesandgrasscovercropsinthemixture(e.g.,growingS.
cerealeinmixturewithsoybean,usingbothascovercrops)islikelytodecreasetheseedproduction
byweeds,andhenceareducedweedseedbankisexpectedwiththiskindofcovercropapplication
[98].
CovercropmulchesinvegetableproductionsystemsoftheUnitedStatescouldprovidefields
freeofweeds:importantcovercropswereoilseedradish(RaphanussativusL.),S.albaandB.juncea[99].
Similarly,legumecovercropsvelvetbean(Mucunadeeringiana(Bort)Merr.),jumbiebean(Leucaena
leucocephala(Lam.)deWit),jackbean(Canavaliaensiformis(L.)DC.)]aretraditionallyusedinMexico
forcontrollingweedsinfieldcropsandachievingotherecologicalbenefitsofcovercrops,suchas
improvedsoilfertility[100].
Anumberofmulches—V.villosa,Egyptianclover(T.alexandrinumL.),A.sativa,T.
meneghinianum,wheat(TriticumaestivumL.),S.cereale,V.sativa,L.multiflorum—weretestedfortheir
weedcontrolefficacyintomato[49].Thecovercropswerekilledbeforetransplantingtomato
seedlings.Outofthetestedmulches,twomulches,i.e.,L.multiflorumandS.cerealedecreasedthe
weedbiomassbymorethan75%.Twooftheotherofmulches(V.sativaandV.villosa)werealso
Agronomy2020,10,25710of16
effectiveforweedcontrolintomato[49].Similarly,V.villosaasacovercropintomatoproduceda
biomassof7.49tha1,andthemulchfromthiscovercropdecreasedthebiomassofsomeweed
species(A.retroflexus,D.sanguinalis,P.oleracea)by40%,andtheirdensityby>70%intomato[89,90].
Inanotherstudy,S.cerealewasgrownasacovercropanddesiccatedtostayasmulchoneweek
beforeplantingtomato.However,inthisstudy,additionalweedcontrolmeasureswererequiredto
achievesatisfactoryweedcontrol[101].Inanotherstudy,covercropssuchasT.incarnatumandV.
villosaeffectivelycontrolledtheweedsintomatoproductionbutdidnotimprovethetomatoyield
[102].
Amongseveralcoverspecies,themosteffectiveforweedcontrolincabbage(Brassicaoleracea
var.capitata)wereS.bicolor,sudangrass(Sorghumsudanense(P)Stapf.),andV.villosa,whichcaused
thehighestdecreaseinweedbiomassanddensity[50].Covercropswereeffectiveinsuppressing
weedssuchasA.retroflexus,Europeanheliotrope(HeliotropiumeuropaeumL.),P.oleraceae,field
pennycress(ThlaspiarvenseL.),annualsowthistle(SonchusarvensisL.),blacknightshade(Solanum
nigrumL.),shepherd’spurse(Capsellabursapastoris(L.)Medik),C.album,sunspurge(Euphorbia
helioscopiaL.),wildmustard(SinapisarvensisL.),etc.,foralmosttwomonths.WeedcontrolbyV.
villosadoubledthekale(BrassicaoleraceaL.var.acephalaDC)yieldcomparedtountreatedcontrol
[50].Incucumberproduction,thephysicalpressureandallelopathiceffectsof(S.bicolor×S.
sudanense.)andS.cerealehelpedtocauseamorethan80%decreaseinweeddensities[14].V.villosa
wasalsoeffectiveincontrollingweedsbutityieldedsimilartocontroltreatment.Nevertheless,S.
cerealeandS.bicolor×S.sudanensesignificantlyincreasedthecucumberyieldovercontrol[14].
Lettuceisextensivelyusedasasaladaswellasinthemakingofrolls,wraps,sandwichesand
severalotherrecipes.Aslettuceismostlyconsumedasfreshleaves,nonchemicalpestcontrolis
moreimportantforthisvegetablecrop.Alongwithothernonchemicalmethods,covercropshave
alsobeeninvestigatedforweedcontrolinlettucefields[17].Forexample,thecovercropofcowpea
(V.unguiculata(L.)Walp.)(growninsummerandtheneitherkeptasmulchorincorporatedinthe
soilduringfall)hadveryfewweedspeciesandhigherlettuceyieldscomparedtotheothercover
crop,S.vulgare,orthefallowtreatment[17].Inpepperproduction,thecovercropspecieswiththe
highestcompetitivenessagainstweedswereoat(AvenasativaL.),L.multiflorum,commonvetch
(ViciasativaL.)andV.villosa[103].Bytheendofthefirstandsecondmonthsofcovercrop
incorporation,theV.villosahadthehighestweedsuppression(70%orhigher)andtheplotswiththe
samecovercrophadthehighestpepperyield[103].Similarly,cowpeaasacovercropwasalso
effectiveinweedcontrolinpepperproduction,alongwithanincreaseinthegrowthandbiomass
productionofpepperplants[104].
Ladinoclover(TrifoliumrepensL.)asacovercropresiduewaseffectivetosuppressweedsin
squash(CucurbitamaximaDuch.)atfourweeksafterplanting;however,theeffectivenessofthecover
croptoaffectweedswasdiminishedbytheendofthesecondmonthofplanting[105].Inanother
study,S.cerealeandH.vulgareascovercropsinsugarbeet(BetavulgarisL.)suppressedweedssuchas
D.sanguinalis,hookedbristlegrass[Setariaverticillata(L.)P.Beauv.],andE.crusgalli.Thisweed
suppressionwaslikelyduetotheallelopathicpotentialofH.vulgareandS.cereale[106].V.villosa,S.
cereal,oramixtureofthesetwocovercropswasevaluatedfortheirweedcontrolabilityinsweet
corn.Eitheraloneorinamixture,thetwocovercropssuppressedtheweedsandincreasedtheyield
ofsweetcorn[107].Similarly,inanotherstudy,covercropssuchasS.cereale,V.villosa,andwheat
suppressedtheearlyseasonweedsbynearly50%insweetcorn.However,thecovercropswerenot
effectiveincontrollingsedgeweeds.WheatandS.cerealeasacovercroporamixtureofthesewith
V.villosahadanegativeeffectontheyieldofsweetcorn[108].
Generally,itisassumedthatweedcontrolthroughcovercropsinvegetablescanbeimproved
byusingamixtureofcovercropsbelongingtodifferentfunctionalgroups[109].However,thismay
notalwaysbetrue.Forexample,thirteenmixturesofcovercropswereevaluatedfortheirweed
suppressioninvegetables[110].Mixturesofanycovercropspoorlysuppressedweedsifthemixture
wasapoorweedcompetitororhadpoormechanicaldesiccation.Importantly,individualcover
cropsthatperformedwellwithgoodestablishmentandweedcompetitionalsoperformwellwhen
growninmixtures.Covercropsthatperformedwellbothasindividualcropsandinamixturewere
Agronomy2020,10,25711of16
H.vulgare,S.cereale,V.villosa,andT.incarnatum,andtheseweresubsequentlyusedforweedcontrol
intomato[110].Inanotherstudy,theuseofcovercropsinnotillplantedvegetablescouldhighly
decreasetheemergenceofhairynightshade(SolanumsarrachoidesSendtn.)andPowell’samaranth
(AmaranthuspowelliiS.Watson)[111].
Incontrasttoconventionalstudiesthatdeterminetheeffectofcovercropsonweedcontrolin
vegetables,someinnovativetechniqueshavealsobeeninvestigated.Forexample,S.cerealecover
cropinoculatedwiththeplantbeneficialfungusTrichodermavirenscouldcontrolweedsin
transplantedvegetables[112].However,thenumberofsuchstudiesisverylimited.
8.IntegrationofCoverCropswithVegetableCrops
Thereisagoodopportunitytogrowcovercropsduringthefallowperiod.Thecovercrops
grownduringthefallowperiodrestrictthegrowthofweedsandseedestablishment,hence
providingweedfreefieldsfortheupcomingvegetablecropseason.Forexample,S.cereale,R.sativus
andB.napuswerestronginhibitorsofweedsduringthefallowperiod[113].Covercropsaresown
onetotwomonths(orafewweeks)priortothesowingofthemaincropandthendesiccatedor
killed.Insomeinstances,covercropsandvegetablescangrowtogetherforaperiodofafewweeks.
Alongwiththeuseofglyphosate,theuseofmechanicalkillingofcovercropshasalsobeen
proposed.Desiccationofcovercropsmaybeeasywhenitisperformedduringflowering,or
immediatelybeforeorafterthisperiod.EasymechanicalmanipulationofcovercropssuchasH.
vulgare,bigflowervetch(ViciagrandifloraScop.),S.cereale,T.subterraneum,crimsonclover(Trifolium
incarnatumL.),andV.villosawasachievedwhencropswereatbloomorpostbloomstage[114].
CovercropswereplantedattheendofMarchandharvestedintwomonths(endofMay),andthe
maincropswereplantedwithinaweek.Undercutterwasabetterterminatorthanfielddisksin
reducingthebiomassofgrassweedsandincreasingsoybeanandmaizeyields[115].Covercrop
managementshouldbedonewithregardtotheactionmechanismofcovercropsagainstweeds.For
instance,ifacovercrophasahighallelopathicactivity,itmaybemixedintothesoilafteritskilling.
However,ifthecovercropsuppressesweedsthroughitsshadingoraphysicaleffect,thenitmaybe
leftscatteredonthesoilafterdesiccation[116].
9.Conclusions
Nonchemicalweedcontrolisdesiredanditisimportantinvegetablecropsforseveralreasons.
Withrisingconcernsregardingherbicideevolutioninweedsandherbicideresidueissuesinthe
ediblepartsofvegetables,itisnecessarytoattemptweedcontrolinvegetablesthroughtechniques
suchascovercrops.Thediscussioninthisreviewshowsthatseveralcovercropssuppressweedsin
vegetablecropsthroughtheirphysicalorallelopathiceffects.Nevertheless,widespread
implementationofcovercropsacrosstheworldislacking.Technologicalgapsandlackof
sitespecificexperimentationmaybereasonsbehindthis.Localscaleexperimentationandbridging
thetechnologicalgapscanaidinawidespreadutilityofcovercropsforsustainableweedcontrolin
vegetableproduction.
Funding:Thisresearchreceivednoexternalfunding
ConflictsofInterest:Theauthorsdeclarenoconflictsofinterest
References
1. Oerke,E.C.Croplossestopests.J.Agric.Sci.2006,144,31–43.
2. AmpongNyarko,K.;DeData,S.K.AHandbookforWeedControlinRice;InternationalRiceResearch
Institute:Manila,Philipines,1991.
3. Pimentel,D.;McLaughlin,L.;Zepp,A.;Lakitan,B.;Kraus,T.;Kleinman,P.;Vancini,F.;Roach,W.J.;
Graap,E.;Keeton,W.S.;etal.EnvironmentalandeconomicimpactsofreducingU.S.agriculturalpesticide
use.InHandbookofPestManagementinAgriculture;Pimentel,D.,Ed.;CRCPress:BocaRaton,FL,USA,
1991;pp.679–720.
Agronomy2020,10,25712of16
4. Brown,B.;Hoshide,A.K.;Gallandt,E.R.Aneconomiccomparisonofweedmanagementsystemsusedin
smallscaleorganicvegetableproduction.Org.Agric.2019,9,53–63.
5. Schroeder,D.;MüllerSchärer,H.;Stintson,C.S.A.AEuropeanweedsurveyin10majorcropsystemsto
identifytargetsforbiologicalcontrol.WeedRes.1993,33,449–458.
6. Kropff,M.J.;Walter,H.EWRSandtheChallengesforWeedResearchattheStartofANewMillennium.
WeedRes.2000,40,7–10.
7. Jabran,K.;ChauhanBS.Overviewandsignificanceofnonchemicalweedcontrol.InNonChemicalWeed
Control;Elsevier:2018;pp.1–8.
8. Dabney,S.M.;Murphree,C.E.;Triplett,G.B.;Grissinger,E.H.;Meyer,L.D.;Reinschmiedt,L.R.;Rhoton,
F.E.Conservationproductionsystemsforsiltyuplands.InProceedingsofthe1993SouthernConservation
TillageConferenceforSustainableAgriculture,Monroe,LA,USA,17June1993;43–48.
9. Sainju,U.M.;Singh,B.P.Nitrogenstoragewithcovercropsandnitrogenfertilizationintilledand
nontilledsoils.Agron.J.2008,100,619–627.
10. Ngouajio,M.;Foko,J.;Fouejio,D.Thecriticalperiodofweedcontrolincommonbean(Phaseolusvulgaris
L.)inCameroon.CropProt.1997,16,127–133.
11. Chandler,J.M.;Cooke,F.T.Economicsofcottonlossescausedbyweeds.InWeedsofCotton;McWhorter,
C.G.,Abernathy,J.R.,Eds.;TheCottonFoundation:Memphis,Tennessee,USA;1992;pp.85–116.
12. Vargas,R.;Fischer,W.B.;Kempen,H.M.;Wright,S.D.Cottonweedmanagement.InCottonProduction;
Johnson,M.S.,Kerby,T.A.,Hake,K.D.,Eds.;UCDANRPub;Oakland,CA,USA,1996;pp.187–202.
13. Teasdale,J.R.Contributionofcovercropstoweedmanagementinsustainableagriculturalsystems.J.
Prod.Agric.1996,9,475–479.
14. Ngouajio,M.;Mennan,H.Weedpopulationsandpicklingcucumber(Cucumissativus)yieldunder
summerandwintercovercropsystems.CropProt.2005,24,521–526.
15. Mennan,H.;Ngouajio,M.;Isik,D.;Kaya,E.Effectofalternativemanagementsystemsonweed
populationsinhazelnut(CorylusavellanaL.).CropProt.2006,25,835–841.
16. Norsworthy,J.K.;Malik,M.S.;Jha,P.;Riley,M.B.SuppressionofDigitariasanguinalisandAmaranthus
palmeriusingautumnsownglucosinolateproducingcovercropsinorganicallygrownbellpepper.Weed
Res.2007,47,425–432.
17. Ngouajio,M.;McGiffenM.E.,Jr.;Hutchinson,C.M.Effectofcovercropandmanagementsystemonweed
populationsinlettuce.CropProt.2003,22,57–64.
18. Samarajeewa,K.B.D.P.;Horiuchi,T.;Oba,S.Fingermillet(EleucinecorocanaL.Gaertn.)asacovercropon
weedcontrol,growthandyieldofsoybeanunderdifferenttillagesystems.SoilTill.Res.2006,90,93–99.
19. Teasdale,J.R.;Brandsaeter,L.O.;Calegari,A.;Neto,F.S.;Upadhyaya,M.K.;Blackshaw,R.E.Covercrops
andweedmanagement.InNonchemicalWeedManagement:Principles,ConceptsandTechnology;Upadhyaya,
M.K.,Blackshaw,R.E.,Eds.;CABInternational,CambridgeMassachusettsUSA;2007;pp.49–64.
20. Fisk,J.W.;Hesterman,O.B.;Shrestha,A.,Kells,J.J.;Harwood,R.R.;Squire,J.M.;Sheaffer,C.C.Weed
suppressionbyannuallegumecovercropsinnotillagecorn.Agron.J.2001,93,319–325.
21. Reddy,K.N.Impactofryecovercropandherbicidesonweeds,yield,andnetreturninnarrowrow
transgenicandconventionalsoybean(Glycinemax).WeedTechnol.2003,17,28–35.
22. Teasdale,J.R.;Daughtry,C.S.Weedsuppressionbyliveanddesiccatedhairyvetch(Viciavillosa).WeedSci.
1993,41,207–212.
23. Altieri,M.A.;Lana,M.A.;Bittencourt,H.V.;Kieling,A.S.;Comin,J.J.;Lovato,P.E.Enhancingcrop
productivityviaweedsuppressioninorganicnotillcroppingsystemsinSantaCatarina,Brazil.J.Sustain.
Agric.2011,35,855–869.
24. Hoffman,M.L.;Weston,L.A.;Snyder,J.C.;Regnier,E.E.Allelopathicinfluenceofgerminatingseedsand
seedlingsofcovercropsonweedspecies.WeedSci.1996,44,579–584.
25. Weiner,J.Anewneighborhoodmodelforannualplantinterference.Ecology1982,63,1237–1241.
26. Pike,D.R.;Stoller,E.W.;Wax,L.M.Modellingsoybeangrowthandcanopyapportionmentin
weedsoybean(Glycinemax)competition.WeedSci.1990,38,522–527.
27. Obopile,M.;Munthali,D.C.;Matilo,B.Farmers’knowledge,perceptionsandmanagementofvegetable
pestsanddiseasesinBotswana.CropProt.2008,27,1220–1224.
28. Akemo,M.C.;Regnier,E.E.;Bennett,M.A.Weedsuppressioninspringsownrye(Secalecereale)–pea
(Pisumsativum)covercropmixes.WeedTechnol.2000,14,545–549.
Agronomy2020,10,25713of16
29. Roberts,H.A.;Hewson,R.T.,Ricketts,M.A.Weedcompetitionindrilledsummerlettuce.Hortic.Res.1997,
17,39–45.
30. Lanini,W.T.;LeStrange,M.Lowinputmanagementofweedsinvegetableelds.Calif.Agric.1991,45,11–
13.
31. Dusky,J.A.;Stall,W.M.Weedmanagementpracticesforlettuceproductionusingimazethapyr.In
Proceedingsofthe108thFloridaStateHorticulturalSociety,LakeAlfred,FL,USA,October2224,1995,
pp.204–207.
32. Shreer,J.W.;Dusky,J.A.;Shilling,D.G.;BreckeBJ.;Sanchez,C.A.Effectsofphosphorusfertilityon
competitionbetweenlettuce(LactucasativaL.)andspinyamaranth(AmaranthusspinosusL.).WeedSci.
1995,42,556–560.
33. GreenTracewicz,E.;Page,E.R.;Swanton,C.J.Lightqualityandthecriticalperiodforweedcontrolin
soybean.WeedSci.2012,60,86–91.
34. MoralesPayan,J.P.;Santos,B.M.;Stall,W.M.;Bewick,T.A.Effectsofpurplenutsedge(Cyperusrotundus)
ontomato(Lycopersiconesculentum)andbellpepper(Capsicumannuum)vegetativegrowthandfruityield.
WeedTechnol.1997,11,672–676.
35. AmadorRamirez,M.D.Criticalperiodofweedcontrolintransplantedchillipepper.WeedRes.2002,42,
203–209.
36. Monaco,T.J.;Grayson,A.S.;Sanders,D.C.Influenceoffourweedspeciesonthegrowthandqualityof
directseededtomatoes(Lycopersiconesculentum).WeedSci.1981,29,394–397.
37. Price,A.J.;Norsworthy,J.K.Covercropsforweedmanagementinsouthernreducedtillagevegetable
croppingsystems.WeedTechnol.2013,27,212–217.
38. Dettmann,R.L.;Dimitri,C.Who’sbuyingorganicvegetables?DemographiccharacteristicsofUS
consumers.J.FoodProd.Mark.2009,16,79–91.
39. Heap,I.Herbicideresistantweeds.InIntegratedPestManagement;SpringerDordrechtSwitzerland:2014;
pp.281–301.
40. Pala,F.;Mennan,H.Socioeconomicandenvironmentaleffectsofglyphosateconsumption.In
Proceedingsofthe3rdAnatolianInternationalCongressofAppliedSciences,Diyarbakir,Turkey,28–29
December2019.
41. Coombs,C.;Lauzon,J.D.;Deen,B.;VanEerd,L.L.Legumecovercropmanagementonnitrogendynamics
andyieldingraincornsystems.FieldCropsRes.2017,201,75–85.
42. Sturm,D.J.;Peteinatos,G.;Gerhards,R.Contributionofallelopathiceffectstotheoverallweed
suppressionbydifferentcovercrops.WeedRes.2018,58,331–337.
43. Akbari,P.;Herbert,S.J.;Hashemi,M.;Barker,A.V.;Zandvakili,O.R.RoleofCovercropsandplanting
datesforimprovedweedsuppressionandnitrogenrecoveryinnotillsystems.Commun.SoilSci.Plant
Anal.2019,50,1722–1731.
44. Snapp,S.S.;Swinton,S.M.;Labarta,R.;Mutch,D.;Black,J.R.;Leep,R.;Nyiraneza,J.;O’Neil,K.Review
andInterpretation:EvaluatingCoverCropsforBenefits,Costs,andPerformancewithinCroppingSystem
Niches.Agron.J.2005,97,322–332.
45. Couëdel,A.;Kirkegaard,J.;Alletto,L.;Justes,E.Cruciferlegumecovercropmixturesforbiocontrol:
Towardanewmultiserviceparadigm.Adv.Agron.2019,157,55–139.
46. Creamer,N.G.;Bennett,M.A.;Stinner,B.R.;Cardina,J.;Regnier,E.E.Mechanismsofweedsuppressionin
covercropbasedproductionsystems.Am.Soc.Hortic.Sci.1996,31,410–413.
47. RebergHorton,S.C.;Grossman,J.M.;Kornecki,T.S.;Meijer,A.D.;Price,A.J.;Place,G.T.;Webster,T.M.
UtilizingcovercropmulchestoreducetillageinorganicsystemsinthesoutheasternUSA.Renew.Agric.
FoodSyst.2012,27,41–48.
48. Mirsky,S.B.;Ryan,M.R.;Teasdale,J.R.;Curran,W.S.;RebergHorton,C.S.;Spargo,J.T.;Wells,M.S.;
Keene,C.L.;Moyer,J.W.Overcomingweedmanagementchallengesincovercrop–basedorganic
rotationalnotillsoybeanproductionintheeasternUnitedStates.WeedTechnol.2013,27,193–203.
49. Mennan,H.;Ngouajio,M.;Isık,D.;Kaya,E.Effectsofalternativewintercovercroppingsystemsonweed
suppressioninorganicallygrowntomato(Solanumlycopersicum).Phytoparasitica2009,37,385–396.
50. Mennan,H.;Ngouajio,M.;Kaya,E.;Isık,D.Weedmanagementinorganicallygrownkaleusing
alternativecovercroppingsystems.WeedTechnol.2009,23,81–88.
51. Hayden,Z.D.;Brainard,D.C.;Henshaw,B.;Ngouajio,M.Winterannualweedsuppressioninrye–vetch
covercropmixtures.WeedTechnol.2012,26,818–825.
Agronomy2020,10,25714of16
52. Lawley,Y.E.;Teasdale,J.R.;Weil,R.R.Themechanismforweedsuppressionbyaforageradishcover
crop.Agron.J.2012,104,205–214.
53. Brennan,E.B.;Smith,R.F.Wintercovercropgrowthandweedsuppressiononthecentralcoastof
California.WeedTechnol.2005,19,1017–1024.
54. Boyd,N.S.;Brennan,E.B.;Smith,R.F.;Yokota,R.Effectofseedingrateandplantingarrangementonrye
covercropandweedgrowth.Agron.J.2009,101,47–51.
55. Cressman,S.T.;Page,E.R.;Swanton,C.J.Weedsandtheredtofarredratioofreflectedlight:
Characterizingtheinfluenceofherbicideselection,dose,andweedspecies.WeedSci.2011,59,424–430.
56. Rajcan,I.;Chandler,K.J.;Swanton,C.J.Red–farredratioofreflectedlight:Ahypothesisofwhy
earlyseasonweedcontrolisimportantincorn.WeedSci.2004,52,774–778.
57. Mirsky,S.B.;Gallandt,E.R.;Mortensen,D.A.;Curran,W.S.;Shumway,D.L.Reducingthegerminable
weedseedbankwithsoildisturbanceandcovercrops.WeedRes.2010,50,341–352.
58. Moonen,A.C.;Barberi,P.Sizeandcompositionoftheweedseedbankafter7yearsofdifferentcovercrop
maizemanagementsystems.WeedRes.2004,44,163–177.
59. Mirsky,S.B.;Curran,W.S.;Mortenseny,D.M.;Ryany,M.R.;Shumway,D.L.Timingofcovercrop
managementeffectsonweedsuppressioninnotillplantedsoybeanusingarollercrimper.WeedSci.2011,
59,380–389.
60. Brennan,E.B.;Boyd,N.S.;Smith,R.F.;Foster,P.Seedingrateandplantingarrangementeffectsongrowth
andweedsuppressionofalegumeoatcovercropfororganicvegetablesystems.Agron.J.2009,101,979–
988.
61. Jabran,K.;Mahajan,G.;Sardana,V.;Chauhan,B.S.Allelopathyforweedcontrolinagriculturalsystems.
CropProt.2015,72,57–65.
62. Jabran,K.ManipulationofAllelopathicCropsforWeedControl,1sted.;SpringerNatureInternational
Publishing:Cham,Switzerland,2017.
63. Jabran,K.Ryeallelopathyforweedcontrol.InManipulationofAllelopathicCropsforWeedControl;Springer:
Cham,Switzerland,2017;pp.49–56.
64. Tabaglio,V.;Marocco,A.;Schulz,M.Allelopathiccovercropofryeforintegratedweedcontrolin
sustainableagroecosystems.Ital.J.Agron.2013,8,e5.
65. Chase,W.R.;Nair,M.G.;Putnam,A.R.2,2′‐oxo1,1′‐azobenzene:Selectivetoxicityofrye(SecalecerealeL.)
allelochemicalstoweedandcropspecies:II.J.Chem.Ecol.1991,17,9–19.
66. Yenish,J.P.;Worsham,A.D.;Chilton,W.S.DisappearanceofDIBOAglucoside,DIBOA,andBOAfrom
rye(SecalecerealeL.)covercropresidue.WeedSci.1995,43,18–20.
67. Haramoto,E.R.;Gallandt,E.R.Brassicacovercropping:I.Effectsonweedandcropestablishment.Weed
Sci.2005,53,695–701.
68. Petersen,J.;Belz,R.;Walker,F.;Hurle,K.Weedsuppressionbyreleaseofisothiocyanatesfrom
turniprapemulch.Agron.J.2001,93,37–43.
69. Kunz,C.;Sturm,D.J.;Varnholt,D.;Walker,F.;Gerhards,R.Allelopathiceffectsandweedsuppressive
abilityofcovercrops.PlantSoilEnviron.2016,62,60–66.
70. Williams,M.M.;Mortensen,D.A.;Doran,J.W.Assessmentofweedandcropfitnessincovercropresidues
forintegratedweedmanagement.WeedSci.1998,46,595–603.
71. Krogh,S.S.;Mensz,S.J.;Nielsen;S.T.;Mortensen,A.G.;Christophersen,C.;Fomsgaard,I.S.Fateof
benzoxazinoneallelochemicalsinsoilafterincorporationofwheatandryesprouts.J.Agric.FoodChem.
2006,54,1064–1074.
72. Lovett,J.;Hoult,A.AllelopathyandSelfDefenseinBarley.ACSPubl.1995,170–183,
doi:10.1021/bk19950582.ch013.
73. Oueslati,O.;BenHammoudam,H.;Ghorbel,M.;ElGazzeh,M.;Kremer,R.Roleofphenolicacidsin
expressionofbarley(Hordeumvulgare)autotoxicity.Allelopath.J.2009,23,157–166.
74. Uddin,M.R.;Park,S.U.;Dayan,F.E.;Pyon,J.Y.Herbicidalactivityofformulatedsorgoleone,anatural
productofsorghumrootexudate.PestManag.Sci.2014,70,252–257.
75. Belz,R.G.;Hurle,K.Differentialexudationoftwobenzoxazinoidsoneofthedeterminingfactorsfor
seedlingallelopathyofTriticeaespecies.J.Agric.FoodChem.2005,53,250–261.
76. Wu,H.;Pratley,J.;Lemerle,D.;Haig,T.Evaluationofseedlingallelopathyin453wheat(Triticum
aestivum)accessionsagainstannualryegrass(Loliumrigidum)bytheequalcompartmentagarmethod.
CropPastureSci.2000,51,937–944.
Agronomy2020,10,25715of16
77. Brown,P.;Morra,M.HydrolysisproductsofglucosinolatesinBrassicanapustissuesasinhibitorsofseed
germination.PlantSoil1996,181,307–316.
78. Vaughn,S.F.;Boydston,R.A.Volatileallelochemicalsreleasedbycrucifergreenmanures.J.Chem.Ecol.
1997,23,2107–2116.
79. Inderjit.Plantphenolicsinallelopathy.Bot.Rev.1996,62,186–202.
80. Xuan,T.D.;Hong,N.H.;Khanh,T.D.;Eiji,T.;Tawata,S.;Fukuta,M.Utilizationofplantallelopathyfor
biologicalcontrolofweedsandplantpathogensinrice.InProceedingsoftheFourthWorldCongresson
Allelopathy,WaggaWagga,Australia,2126August,2005.
81. Xuan,T.D.;Chikara,J.;Ogushi,Y.;Tsuzuki,E.;Terao,H.;Khanh,T.D.;Matsuo,M.Applicationofkava
(PipermethysticumL.)rootaspotentialherbicideandfungicide.CropProt.2003,22,873–881.
82. Norsworthy,J.K.;Riar,D.;Jha,P.;Scott,R.C.Confirmation,control,andphysiologyof
glyphosateresistantgiantragweed(Ambrosiatrifida)inArkansas.WeedTechnol.2011,25,430–435.
83. Bernstein,E.R.;Stoltenberg,D.E.;Posner,J.L.;Hedtcke,J.L.Weedcommunitydynamicsandsuppression
intilledandnotillagetransitionalorganicwinterryesoybeansystems.WeedSci.2014,62,125–137.
84. Dube,E.;Chiduza,C.;Muchaonyerwa,P.Conservationagricultureeffectsonsoilorganicmatterona
HaplicCambisolafterfouryearsofmaize–oatandmaize–grazingvetchrotationsinSouthAfrica.SoilTill.
Res.2012,123,21–28.
85. Finney,D.M.;Creamer,N.G.;Schultheis,J.R.;Wagger,M.G.;Brownie,C.Sorghumsudangrassasa
summercoverandhaycropfororganicfallcabbageproduction.Renew.Agric.FoodSyst.2009,24,225–233.
86. Moran,P.;Greenberg,S.Wintercovercropsandvinegarforearlyseasonweedcontrolinsustainable
cotton.J.Sustain.Agric.2008,32,483–506.
87. Silva,E.M.Screeningfivefallsowncovercropsforuseinorganicnotillcropproductionintheupper
midwest.Agroecol.Sustain.FoodSyst.2014,38,748–763.
88. Alcántara,C.;Pujadas,A.;Saavedra,M.ManagementofSinapisalbasubsp.maireiwintercovercrop
residuesforsummerweedcontrolinsouthernSpain.CropProt.2011