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Crop Protection 65 (2014) 105e113
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Crop Protection
journal homepage: www.elsevier .com/locate/cropro
Review
Sustainable weed management in conservation agriculture
Ali Ahsan Bajwa*
Department of Agronomy, University of Agriculture, Faisalabad, 38040, Pakistan
a r t i c l e i n f o
Article history:Received 12 December 2013Received in revised form21 July 2014Accepted 23 July 2014Available online
Keywords:Conservation agricultureSustainabilityWeed dynamicsWeed management
* Tel.: þ92 333 0632018.E-mail addresses: [email protected], aliagr
http://dx.doi.org/10.1016/j.cropro.2014.07.0140261-2194/© 2014 Elsevier Ltd. All rights reserved.
a b s t r a c t
Sustainable crop production is necessary to ensure global food security and environmental safety.Conservation agriculture (CA) is gaining popularity around the globe due to its sustainable approachessuch as permanent soil cover, minimal soil disturbance, planned crop rotations and integrated weedmanagement. Weed control is the biggest challenge to CA adoption. Weed ecology and management isdifferent in CA than in conventional agriculture. In CA, weeds expression, seed bank status, distribution,dispersal mechanisms, diversification, growing patterns and competition trends are complex and differfrom conventional systems. It is due to reduced tillage of the soil and the flora that thrives in CA. Reducedtillage systems affect the efficacy of herbicides and mechanical weed control measures. So, it is animportant task to find out the differences and to fabricate new management options. In this review,changing weed dynamics have been framed. A novel aspect of this review is the comprehensive accountof sustainable weed management strategies in relation to CA. Modified tillage operations, improvedcultural practices, bioherbicides, chemical herbicides, allelopathy, and crop nutrition have been identifiedas suitable weed management tools. None of these offers complete control but the integration of thesetools in suitable combinations works efficiently. Weeds dominating CA and their responses to CAcomponents are highlighted. For example, small seeded and perennial weeds are more abundant in CA.The role of herbicide resistance in weeds and herbicide tolerant (HT) crops in CA is also highlighted.Allelopathy and crop nutrition are discussed as modern weed management tools for CA. A detailed ac-count of weed responses to fertilizer management options is also given. Integrated weed managementcompatible to cropping patterns and climatic conditions offers the best results in CA. Future efforts mustbe directed towards the optimization and integration of these weed management practices.
© 2014 Elsevier Ltd. All rights reserved.
1. Introduction
Crop production is important component of agriculture which isresponsible for global food security. Effective crop production be-gins with successful soil management which is first and foremostprinciple of agronomy. Modern day agriculture is strongly associ-ated with conventional tillage which is defined as a system havingdeep primary tillage followed by secondary cultivation operations(Holland, 2004). The practice of tillage in agriculture began thou-sands of years ago at the time when humans being shifted fromhunting and gathering towards the raring of animals and settleddown in productive areas near rivers like the Nile, Euphrates,Yangste and Indus (Hillel, 1991). The concept of tillage was preva-lent in Mesopotamia in 3000 B.C. (Hillel, 1998; Lal, 2001). Tillage isthe manipulation of soil for the betterment of aggregates for the
development of a well pulverized and suitable seed bed prior tosowing. It is a multipurpose practice that aids in proper emergenceof seeds due to optimum placement providing sufficient amountsof water, light and nutrients. It ensures the availability of nutrientsand provides aeration of the soil layer (Reicosky and Allmaras,2003). Different soil amendments are also added to the soilthrough tillage. It also helps in control of soil-borne diseases andpests (Owens, 2001). Tillage is an essential part of conventionalagriculture for soil preparation, residue incorporation, planting andherbicides incorporation (Sherestha et al., 2006).
Besides all the plus points, conventional tillage is playing havocto natural landscape and soil fertility. Heavy tillage implements areextensively used in conventional tillage system without consid-ering the soil capability and fertility status. Increasing costs of en-ergy sources, labor and other inputs are making this systemunsuitable and unfeasible due to high cost of production (Edwardsand Smith, 2005). Moreover, this system is problematic for envi-ronmental safety and global protection but conservation agricul-ture (CA) is a viable alternate which is suitable for today's limited
A.A. Bajwa / Crop Protection 65 (2014) 105e113106
natural resources and changing climate (Montgomery, 2007). That'swhy it is becoming a common approach in rainfed areas for waterand soil conservation. About 45 million hectares have been re-ported under CA (FAO, 2001). CA is a broad spectrum and multi-dimensional term. CA defined by FAO (2001) as minimal soildisturbance (no-till, NT) and permanent soil cover (mulch) com-bined with rotations, is a recent agricultural management systemthat is gaining popularity in many parts of the world (Hobbs et al.,2008). The trend is spreading quickly in North and South America,semi-arid and tropical regions of the world (Lal, 2000). CA isdesigned to be an effective solution to agricultural problems insmall land holding farming communities especially in tropical re-gions (Fowler and Rockstrom, 2001; Derpsch, 2003; Hobbs, 2007;Hobbs et al., 2008; Giller et al., 2009). Most important principlesof CA (Minimal soil disturbance and permanent soil cover) areachieved by no tillage, zero tillage, minimum tillage/ridge tillage,reduced tillage, direct seeding and mulch tillage (Reicosky andAllmaras, 2003). All these practices are collectively called conser-vation tillage. These are used according to farming system, croppingpattern and climatic conditions (Reicosky and Allmaras, 2003;Giller et al., 2009). Zero tillage is a practice of least soil distur-bance during single tillage operation to avoid soil degradation. It ismainly planting operation but also involve slight manipulation ofsoil. It has also been widely accepted by farmers in developedcountries (Bolliger et al., 2006; Triplett and Warren, 2008). Theprecise and accurate definition of CA is very difficult to quote due todiverse climatic conditions and variable management practicesaround the globe. It varies according to the area and geographical aswell as climatic conditions (Carter, 1994; Lyon et al., 2004).
Weed management has been recognized as essential compo-nent of CA and, thus, requires special attention. Weeds act differ-ently in different habitats. Weeds also provide habitat for insectsand disease-causing pests which can reduce the quality of the cropand increase the risk of crop failure. Tillage provides different typesof natural and manipulated habitats to the weeds. Tillage plays animportant role in weed control and has been used as an effectivetool since ancient times. Tillage practices are still very effective;different types of modern cultivators and weeders are facilitatingmechanical weed management (Wallace and Bellinder, 1992). CAalso provides a specific set of environmental factors that affectweed populations. Weed infestations in CA is a major concern and akey reason for reluctant approach of farmers towards its adoption(Buhler et al., 1994). CA is mainly focused on minimal tillage withspecific herbicide applications for better weed control (Lafondet al., 2009). Weed management in CA is a relatively complexapproach involving different tillage practices, agronomic practices,engineering approaches and modern technologies of crop estab-lishment (Lafond et al., 2009).
CA requires dedicated efforts to control weeds initially; how-ever, after maintaining a certain threshold level, it is easier tomanage weed infestations in these systems. Integrated approachesmust be considered and optimized to have proper weed control inCA. It is necessary to study the ecological, biological and social is-sues related to weeds in CA. Moreover, a systematic approach isneeded to optimize different sets of management options based onecological and geographic features of a particular agro-ecosystem.It will help to determine new lines of action regarding site-specific weed management and sustainable control. Future en-deavors in this regard must be oriented in such a direction to offercomprehensive solutions keeping a focus on the differences.
2. Weed dynamics in CA
Weeds are plants with specific characteristics that help theminfest and invade crops and succeed under a wide range of
environmental and climatic conditions (Labrada and Parker, 1994).CA promotes certain types of weeds including annuals, biennialsand perennials. Certainweeds decrease after consistent practices ofCA but some others may increase (Chauhan et al., 2006a). CA sys-tems with low soil disturbance tend to leave more weed seeds onthe surface, whereas high disturbance systems bury weeds(Chauhan et al., 2006b). Usually, small-seeded weed species arefavored more in CA (Sosnoskie et al., 2006). Typically, small-seededweed species thrive in CA compared to conventional tillage becausethe seed is not buried. The small-seeded species cannot germinateas readily from buried depths as they can from the soil surface.Weed emergence is less because of reduced soil manipulation in CA(Chauhan et al., 2007). There are many annual weeds that germi-nate well under no till system as they can germinate with less or nosoil cover. Biennials also thrive well under CA (Curran et al., 1996).Perennial species can easily produce large populations under CA if afew plants get a good vegetative stand. They have gradual growth inthe first year and proliferate in the second year. Reduced tillagecause changes in weed species, their distribution, densities andcomposition. So, different weeds have different response in CA. Itrequires special approaches for better weed management which issurely a point of interest for adopters of CA (Buhler et al., 1994). CAcan producemore if row crops are introduced in rotation alongwithproper herbicide application (Phillips and Young, 1973).
3. Weed control measures under CA
3.1. Modified tillage
CA has a significant impact over weed populations and, thus, onweed management. Tillage affects weeds through disturbances likecutting, burial, uprooting and dislodgement of weeds; moreover, itchanges the soil climate and influences weed germination, emer-gence and establishment by promoting or inhibiting their move-ment (Clements et al., 1996). Weed flora composition differsaccording to tillage system and, thus, we have to manage them bydifferent approaches. For instance, small-seeded weeds proliferatewell under CA and have to be controlled by special measures(Chauhan et al., 2006a; Sosnoskie et al., 2006). Reduction in tillagemay cause serious problem regarding weed infestations (Buhleret al., 1994). The shift in weed species distribution and weed den-sities poses a great problem for weed management and can cause areduction in crop yield under CA (Blackshaw et al., 2001). Tillagesystems clearly affect weed density, weed distribution and weedseed bank reserves (Table 1).
CA may promote the germination and emergence of newlyproduced weed seeds that stay on or near the soil surface. More-over, the extra residues managed on the surface in CA may cause ahindrance to herbicide efficacy. Perennial, erect or creeping weedsproduce vegetative reproductive parts like rhizomes and tuberswhich are difficult to manage under CA (Shrestha et al., 2003).There is a problem of shift in timing of weed seeds germination andemergence during the course of crop growth which may cause aproblem in the selection of time for herbicide application or othermanagement practices (Bullied et al., 2003).
The shift in weed species has been reported previously but isinconsistent. Cussans (1976) reported the increase in dicot speciesunder no till butWrucke and Arnold (1985) opposed this pattern byattributing the distribution of broadleaved weeds showing similartrend under both conservation tillage and traditional tillage system.Pollard et al. (1982) studied different weeds and concluded thatthere was no proper and consistent trend of different weeds underreduced tillage. Tillage systems influence the emergence of annualand perennial weeds differentially and the vigor of different weedplants also varies significantly (Table 2).
Table 1Weed dynamics under different tillage regimes.
Tillagesystem
Weeds presence Remarks Other details
Above ground Seed bank Above ground þ seed bank
Moldboardplow
Asclepias syriaca, Cyperus esculentus,Echinocloa crusgalli, Eletrigia repens,Polygonum persicaria, Sinapsisarvensis, Taraxaxum officinale
Seteria viridis Abuthilon theophrasti,Ambrosia artemissifolia,Chenopodium album,Plantago major
Most of the weeds areexposed and germinateunder this system, seedbank less developed,less weed density anddiversity overall
Site: Southwestern Ontario, Canada.Soil: Beverley silt loam soil with36% sand, 45% silt, and 19% clay.Organic matter content 3.2% andpH 7.3.Residue cover: Mean percentresidue cover 5.2% for conventionaltillage, 33.0% for chisel plow, 45.9%for ridge-till, and 68.6% for no-till.Cropping system: Corn-soybeanrotation
Chisel plow Amaranthus retroflexus, Cyperusesculentus, Cirsium arvense,Eletrigia repens, Panicumdichotomiflorum, Potentilla recta,Seteria viridis
Physalis heterophylla,Senecio vulgaris,
Abuthilon theophrasti,Ambrosia artemissifolia,Chenopodium album,Plantago major,Taraxaxum officinale
Germinated and reservedseeds are equal, fewseeds from deeper layersare also exposed
Ridge till Asclepias syriaca, Cyperus esculentus,Daucus carota, Eletrigia repens,Erigeron annus, Medicago lupulina,Oxalis strcta, Polygonum persicaria,Rubus idaeus, Sinapsis arvensis,Taraxaxum officinale
Physalis heterophylla,Plantago major,Seteria viridis,Senecio vulgaris,Solidago canadensis
Ambrosia artemissifolia,Cerastium vulgatum,Chenopodium album
Relatively more weeddensity and highestdevelopment of seedbank reserves
No till Abuthilon theophrasti, Asclepiassyriaca, Cirsium arvense, Dactylisglomerata, Daucus carota,Eletrigia repens, Medicago lupulina,Oxalis strcta, Parthenocissusquiquuefolia, Physalis heterophylla,Polygonum persicaria, Rubus idaeus,Seteria glauca, Sonchus oleranceus,Taraxaxum officinale
Echinocloa crusgalli,Fragaria virginiana
Chenopodium album,Plantago major,Seteria viridis
Maximum weeds diversity,many new weedsintroduced, mostlygerminate and very fewadded to seed bank
Extended from Clements et al. (1996).
A.A. Bajwa / Crop Protection 65 (2014) 105e113 107
Tillage system affects perennial weeds more than annual weeds.Maximumweed density, fresh and dry weight under no till systemfollowed by reduced tillage. Weeds can be managed by propertillage operations at different intensities in any cropping system.There are few weeds that are really difficult to manage but still canbe controlled by manipulating the time of cultivation, inter culturepractices and weed control practices. CA may promote differentweeds, however, it is good approach tomanage the weed seed bankand to long-term control of noxious weed species. The best pro-posal for weed management is the integration of different me-chanical practices and reduced cultivation trips in a certain fieldhaving the problem of weed infestation.
3.2. Improved cultural practices
Cultural practices are aimed to ensure better soil and cropmanagement (Nazir, 1994). There are different ways to handleweeds by proper cultural management practices. Effective watermanagement plays a vital role in weed control under CA. The irri-gation scheduling may be done in such a way as to reduce weedpressure in arable crops. Crop rotation is a well-known and provenweed management strategy. Including crop rotation in CA is asuccessful approach to reduce weed pressure. Weeds are normallyset with seasonal emergence and most of them are associated withspecific crops; by changing a crop conventionally coming in prev-alent sequence may reduce the chances of particular weed in-festations and, thus, may reduce the weed pressure. Planned croprotations may cause germination of dormant weeds and thencontrol major weeds efficiently (Table 3).
Weed seeds may dominate if sufficient moisture is available atthe time of crop sowing but stale bed method of land preparationmay cause inhibition of weeds significantly. If dust mulch is createdby shallow cultivation followed by dry period then crop seed (cornand vegetables) can be sown in weed free soil. It may improve thecrop establishment and suppress weeds without supplementalirrigation. Row crop cultivation is also a good approach to
accomplish the management of weeds under reduced tillage. It isvery effective to combine the chemical approach and row cropcultivation maintaining high residues in the field. In such systems,heavy tillage implements are also used that pass through a largerarea in the field uprooting the emerged weed seedlings. Similarlyunder ridge till systems the cultivator used allows more residues tostay on the surface. The residues and weed seeds are moved fromridge to furrows. In this way, the problem of weed crop competitionis reduced. Mulch tillage is especially designed to retain more than30% crop residues on surface, suppress different weeds due toshading or covering effect. Moreover, different types of organiccompounds released from mulches through leaching cause inhi-bition of weed seed emergence (Ball, 1992). Another approach is theapplication of water in the root zone of crop plants by drip irriga-tion without providing moisture to weed seeds present on or nearthe surface. Direct seeding is also an effective approach to havebetter weed control over certain weed species in rice by optimumuse of herbicides (Farooq et al., 2011a). Use of cover crops incombination with tillage operations favors weed suppression. Forinstance, rapeseeds and sudangrass as cover crops may control avariety of weeds in conservation systems. Crop competition itself isa useful practice to handle weeds. We may set the planting ge-ometry of different crops in such a way to increase inter specificcompetition and less amounts of light, water and nutrients will beavailable to the weeds present between closely grown rows of cropplants.
3.3. Mulching and soil cover
Any material used to cover the soil to conserve moisture and toprotect the plant is mulch (Creamer et al., 1995). It covers the soilwhen there is no vegetation. If mulching is done on fallow land itmay suppress different weeds by impeding light and air. Differenttypes of organic mulches like straw mulch, hay mulch, municipalwaste mulch, manure mulch and chip board mulch can controlweeds effectively (Makus et al., 1994; Campiglia et al., 2009).
Table 2Effect of tillage systems on weeds density and biomass.
Tillage system Weed density (m�2) Fresh wt.(kg m�2)
Dry wt.(kg m�2)
Annual Perennial All weeds
Chenopodium album Echinochloa colonum Cucumis prophetarum Cynodon dactylon Cyperus rotundus
No till 17 62 ab 18 86 a 117 a 300 a 1.37 a 0.27 bReduced till 17 83 a 9 33 b 69 b 211 b 0.97 b 0.22 bDeep till 20 44 b 6 35 b 101 ab 206 b 0.84 b 0.21 b
Source: Arif et al. (2007).
A.A. Bajwa / Crop Protection 65 (2014) 105e113108
Thicker and green organic mulches with more biomass gave betterweed control. Cover crops harvested and left in the field on thesurface may provide the best green mulch having a significantcontrol over certainweeds (Lanini et al., 1989; Creamer et al., 1995).Thick organic mulches cause problems in direct seeded crops butgave good results for transplanted ones (Lanini et al., 1989). How-ever, there are special types of row cleaners available for CA thatclear the rows of residue and improve the herbicide action throughproper penetration. Weed emergence is greatly affected by physicalproperties of mulches (Teasdale and Mohler, 2000). Different ce-reals, vetches, clovers and legumes have been used to obtain suchorganic green mulches (Abdul-Baki and Teasdale, 1993). So, the useof mulching, residues incorporation and cover crops is a pragmaticapproach for weed control in CA.
3.4. Biological weed control
According toWeed Science Society of America biological controlof weeds is broadly defined as “the use of an agent, a complex ofagents, or biological processes to bring about weed suppression. Allforms of macrobial and microbial organisms are considered asbiological control agents.” (http://wssa.net/weed/biological-control/). Weed control through living organisms is an effectiveweed management practice. A large number of predators, patho-gens and other plant competitors of weeds are exploited to kill orsuppress the weeds. A specific combination of organisms maycontrol weeds very effectively in any crop. Remarkable work hasbeen done to explore this environmentally-friendly, safe andeconomical approach for weed control; biological weed control is asuccessful option for integration with other techniques in a CA(Watson, 1991; Müller-Sch€arer et al., 2000). Charudattan (2001)reviewed the importance and effectiveness of many plant patho-gens as bio control agents for noxious weeds. There are severalpotential bio-agents serving as a source for bioherbicides and thusfacilitating eco-friendly weed control (Table 4). We emphasize itsimportance as part of integratedweedmanagement due to its long-term benefits. Bioherbicides have no residual effects in soil orenvironment and crop plants are also free from their influence.
Specific weeds can easily be controlled by applying specificbioherbicides. In short, it is an effective method of weed controlunder any agricultural system and suitable for CA.
Table 3Effect of crop rotations on seed bank and dry matter of Phalaris minor.
Rotation No. of seeds/m2 Seed loss (%) S
Before sowing After harvest 0
Rice-Wheat (Herbicide) 7.8 1.8 77.0 3Rice-Wheat (Control) 8.0 10.3 22.4* (gain) 0Rice-Potato-Sunflower 0.3 0 100 0Rice-Potato-Wheat 0.5 0 100 0Rice-Barseem 0.3 0 100 0Rice-Ghobi sarson 0.8 0.5 37.5 0
The value preceding asterisk is showing a gain. After Brar (2002).
3.5. Chemical weed control
It is the most adopted and perhaps the most effective approachto control weeds all over the world. The chemicals used to kill,weaken or suppress the weeds are called herbicides. They act to killtheweed plants by blocking different physiological functions whichare a must for plant growth. A variety of herbicides are availabledepending upon their mode of action, chemical composition,formulation, selectiveness and efficacy. Most commonly used burndown herbicides are glyphosate, paraquat, glufosinate, 2,4-D anddicamba. The dose and time of application is decided according tovegetation cover present in the field (Vargas and Wright, 2005). Inconventional tillage systems there are no crop residues when pre-emergence herbicides are applied but in the case of CA there areresidues on the surface and may cause interference in herbicidalactivity and reduce their effectiveness (Hartzler and Owen, 1997).Herbicides are applied when annual weeds are young and mostaffected by chemicals. Post emergence herbicides are not influ-enced by tillage practices. Herbicide application rates are typicallythe same for both conventional and CA. Although, there might be alittle effect on their effectiveness and contact due to residues stillnot decomposed. This would probably only be an issue for veryearly post applications or if residue is left standing in the field.Otherwise, the crop should be above the cover crop residue. Themost devastating effect of chemical herbicides is environmentaldegradation. Most of the herbicides being used partially or solely inconservation systems have substantial persistence in soil (Table 5)that cause contamination of underground water as well as degra-dation of microorganisms in rhizosphere (Derksen et al., 1996).
However, a CA farmer must wait a bit longer to apply postemergence herbicides as the crop establishment is not uniformsometime due to suppressive effects of cover crops or heavy resi-dues of previous crop andweed emergence pattern is also different.
3.5.1. Herbicide resistance in weeds and herbicide tolerant cropsContinuous and frequent use of same herbicides induces resis-
tance in weeds against those herbicides occasionally or perma-nently depending upon cultural practices and environmentalconditions (Chaudhry, 2008). The resistant biotype is already there,the continued use of a specific herbicide just selects for the resis-tant biotype (Farooq et al., 2011b). The development of such
eed bank (Seeds/100 g soil) Weed drymatter (kg/ha)
Other details
e7.5 cm depth 7.5e15 cm depth
.5 1.4 200 Site: Punjab IndiaSoil: Clay loam.35 0.15 4550
0 00 00 0
.25 0 13
Table 4Potential bioherbicides for weed management.
Bioherbicide Source organism Weed controlled Target area References
BioChon Chondrostereum purpureum Wild cherry (Prunus serotina) Forests Charudattan (2001),Singh et al. (2003)BioMal or Mallet WP Colletotrichum gloeoporioides Round-leaved mallow (Malva pusilla) e
Camperico Xanthomonas campestris Kentucky bluegrass, Korean velvet grass(Zoysia tenuifolia)
Truf grasses
Collego Colletotrichum gloeosporioides Jointvetch (Aeschynomene virginica) Rice and soybean cropsDe Vine Phytophthora palmivora Strangler vine (Morrenia odorata) Citrus orchardsDr. Biosedge Puccinia canaliculata Yellow nutsedge (Cyperus iria) RiceHakatak Colletotrichum gloeosporioides Silky needlbush (Hakea sericea)Stump Out Cylindrobasium leave Trees
Table 5Persistence of chemical herbicides used in CA.
Herbicide Type Commonly useddose (g/ha)
Half life(Weeks)
Alachlor Selective 1700e4000 4e5Atrazine Selective, also used
as non-selective1500e4500 10e50
Bromoxynil Selective 280e450 1e22,4-D Selective 280e1000 1e4Dicamba Selective 100e400 2e6Glyphosate Non-selective 250e1000 4e8Paraquat Non-selective 560e840 50
Modified from Derksen et al. (1996).
A.A. Bajwa / Crop Protection 65 (2014) 105e113 109
resistant weeds may be due to genetic mutations and adaptivemechanisms. Whatever the mode of resistance, this inducedresistance is problematic for the farming community especially inCA where there is a dependence on chemical herbicides. Intro-duction of herbicide resistant (HR) weeds after the development ofherbicide tolerant (HT) crops have become a serious problem.Tolerant crops to glyphosate (Roundup Ready) (Givens et al., 2009),glufosinate, bromoxynil, imidazolinone (Gealy et al., 2003) anddicamba (Behrens et al., 2007) have been developed. Introductionfollowed by quick and large scale adoption of HT crops like cotton,maize, canola, rice, sugarbeet, alfalfa (James, 2010), brassica andsoybean (Gealy et al., 2003) has revolutionized the CA in developedcountries like USA (Givens et al., 2009) and Australia (Owen et al.,2007). No doubt, HT crops are playing a remarkable role in CAwith weed management becoming easier but a serious problem isthe leakage of resistance genetic traits from crops to associatedweeds (Owen and Zelaya, 2004) however, the appearance of HRweed species from overuse of specific herbicides is most likelymore of an issue. In this regard, judicious use of herbicides isrequired. Efforts are being done to develop HT crops having resis-tance to multiple herbicides. Hence, the use of alternative and newherbicides with different chemical structures and modes of actionis a pragmatic option (Green, 2011). This approach has given superbresults in direct seeded rice all over the world (Table 6).
Table 6Alternative herbicides for herbicide resistant weeds in direct seeded rice.
Alternative herbicide Replaced herbicide Weeds controlled
Quinclorac Propanil Echinochloa crusgalli, Echinochlo
Imazethapyr Propanil Echinochloa crusgalli, Urochloa pBispyribac-sodium Thiobencarb, Monilate Echinochloa crusgalli, EchinochloBenzofenap BenzosufuronBentazon 2,4-DButachlor Sulfonylurea
Extracted from Rao et al. (2007).
Further research is required to develop herbicides with novelmodes of action and improvement of resistance mechanisms of HTcrops employing molecular genetics and biotechnology.
3.6. Use of allelopathy
Allelopathy is a natural, ecological phenomenon in whichdifferent organisms affect the functioning of other organisms intheir vicinity, negatively or positively by releasing secondary me-tabolites (Farooq et al., 2011c). Use of this phenomenon isincreasing in weed management. It is a suitable substitute forsynthetic herbicides since allelochemicals do not have residual ortoxic effects (Bhadoria, 2011). Allelopathy has a vital role to play infuture agriculture as it can be used to control weeds withoutdamaging the natural global beauty of any ecosystem. Moreover, itoffers the management of insect pests and diseases of plantscausing a certain increase in production levels of major crops(Bajwa et al., 2013; Farooq et al., 2013). Allelopathic chemicals havethe potential use as bioherbicides and pesticides (Khalid et al.,2002). Allelopathy can be used by introducing crops with allelo-pathic potential in rotation, using cover crops, spraying plant waterextracts alone, mixed and in combinationwith herbicides to controlweeds (Table 7).
There is a wide range of crops and weeds producing allelopathicchemicals that have the potential to control weeds effectively.Research is being conducted on different plants, bacteria and othermicroorganisms to determine more effective chemicals with alle-lopathic potential. Work on the screening of species having moreallelopathic potential is also under progress. It is a bright and viableoption for sustainable weed management under CA.
3.7. Crop nutrition
Nutrition is a very important aspect in any cropping system andits importance in CA is even more apparent. Fertilizer use hasdefinite influence on weed emergence, weed persistence, weeddormancy, weed dynamics, weed growth and weed dispersion at-tributes. It is necessary to study such interactions in depth to
Origin Reference
a colona Sri Lanka, Costa Rica Valverde et al. (2001),Marambe and Amarasinghe (2002),
latyphylla USA Scherder et al. (2001)a phyllopogon USA De Witt et al. (2002)
Australia Pratley et al. (2004)Malaysia Azmi (2003)South Korea Kim and Ha (2005)
Table 7Allelopathy for weed management.
Allelopathic crop Mode of application Crops benefited Weeds controlled References
Sorghum Water extracts spray Wheat, Cotton,Mungbean, Rice
Chenopodium album, Convolvulus arvensis,Cyperus rotundus, Cyperus iria, Cynodondactylon, Echinocloa colonum,Fumaria indica, Phalaris minor, Rumexdentates, Trianthema portulacastrum
Cheema and Khaliq (2000),Cheema et al. (2002),Wazir et al. (2011)
Sorghum, sunflowerand Brassica
Mixture with water extractsand mixture of waterextract þ herbicide (1/2 dose)
Wheat, Sunflower,Cotton, Canola, Rice
Chenopodium album, Coronopus didymus,Cyperus rotundus, Cyperus iria,Dactyloctenum aegyptium, Echinocloacrusgalli, Melilotus parviflora, Melitotusindica, Phalaris minor, Trianthemaportulacastrum
Cheema et al. (2002),Jabran et al. (2008),Awan et al. (2009),Iqbal et al. (2009)
Sorghum, sunflower,Brassica and rice
Soil mixing and mulching Wheat, Cotton,Maize
Chenopodium album, Convolvulus arvensis,Cyperus rotundus, Cynodon dactylon,Phalaris minor, Trianthema portulacastrum
Cheema and Khaliq (2000),Khaliq et al. (2010)
Sorghum Intercropping Cotton Convolvulus arvensis, Trianthemaportulacastrum
Iqbal et al. (2007)
Rye Cover crop e Amaranthus spp., Portulaca oleracea Nagabhushana et al. (2001)
A.A. Bajwa / Crop Protection 65 (2014) 105e113110
develop safe and pragmatic approaches for weed management insustainable agriculture. CA resulted in improved fertilizer efficiency(10e15%) in the rice-wheat system, mainly a result of betterplacement of fertilizer with the seed drill as opposed to broad-casting with the traditional system (Hobbs et al., 2008). Propermanagement of crop nutrients assures sustainable weed manage-ment through provision of suitable inputs for crop functioning. Itpromotes a healthy competition in which participation of plants isstrong and thus better growth habits are developed.
Weeds show a variety of responses to different fertilizers underdifferent tillage systems depending upon rate and method ofapplication (Evans et al., 2003; Blackshaw and Brandt, 2008;Lindsey et al., 2013). Sensitivity of weeds to fertilization dependson their responding ability in terms of weed growth and nitrogenassimilation. Nutrient availability influences weed crop competi-tion (Evans et al., 2003), however, the response varies with weedspecies type, crop type and nutrient status of soil. Weaver et al.(1992) reported nutrient availability as one of dynamic ap-proaches that can influence duration and extent of competition.Moreover, environmental factors influencing the efficacy and effi-ciency of fertilizers affect weed dynamics and distribution.Sweeney et al. (2008) studied the effect of N on weed emergenceand growth parameters. Results have shown that N influenced thegermination, emergence and competitiveness of different weeds.These parameters may increase or decrease depending on soil typeand climatic conditions.
In short, CA provides a different environment for weed germi-nation, emergence, growth and competition by altering physicaland chemical properties of soil. So, variation in fertilizer doses,application methods and types are needed in accordance withweed responses in such systems. In the future, fertilizer-weed in-teractions in different tillage systems should be focused for scien-tific experimentation to explore specific weed responses, weed-crop competition periods and adaptations to devise new, preciseand pragmatic weed management tools for better crop pro-ductions, food security and food safety.
3.8. Integrated weed management
Integrated weed management (IWM) focus on keeping weedpopulations below a certain threshold level by optimizing thecontrol measures in an organized way. Adoption of herbicides atlarger scale has affected the environment significantly. Societies arenow realizing the concerns over environmental safety and naturalstability and thus working on plans based upon alternative tools
and techniques of weed control (Pannell, 1990; Swanton andWeise,1991; Buhler et al., 2000). Continuous use of herbicides has led toherbicide resistance in weed species. One of the major issues fa-voring the adoption of IWM is the weed management by control-ling biotypes of weeds (Powles and Matthews, 1991; Moss, 1997).Recently, integrated weed management has been employed forweed management and reported as a sustainable approach thatcontrols weeds without reducing crop yield (Swanton and Weise,1991). As declining crop prices, high input cost and environ-mental concerns laid great importance in adopting integratedweedmanagement. In addition, herbicide resistance, persistent weedseed banks are further pushing agricultural researchers to investi-gate integrated approach for weed management (Beckie et al.,2001). IWM involves integration of numerous practices, rightfrom sowing method to chemical control. It is believed that designof cropping systems and practices like crop rotation, cover cropsmight be effective approaches in managing weed control.
In CA, problem of weeds can be controlled by both manualweeding and/or by the use of herbicide. However, labor is becomingexpensive and is rarely available at the critical time of weeding. Tocontrol weeds herbicides are being extensively used in CA, butthere is not a single herbicide that can apply for several types ofweeds present in agricultural fields. Hence, management of weedsby using integrated weed management techniques is highly desir-able to enhance sustainability of CA.
These may consist of using crop residues as mulching, adjustingcrop sowing time, using stale seedbed technique, selecting weedcompetitive cultivars, high seeding rates, narrow row spacing,proper and judicious use of herbicides, use of preventive measuresand following recommended crop rotation as shown in Fig. 1(Chauhan and Mahajan, 2012). In conventional tillage systemsweed control depends on herbicide use and tillage practices butunder the CA, weedmanagement relies on agronomic practices, useof herbicides and no or limited tillage in minimum till systems(Davis et al., 2005; Lafond et al., 2009). Usually it is reported there isless labor required for the land preparation but under the CAwherenoweedicides are used there is moreweed problem and needmorelabor force for weeding (Baudron et al., 2012). Sustainability of CAsystems retain by integrating different strategies of weed man-agement. By applying integrated management practices herbicideuse is also remains profitable and environment friendly over a longperiod of time. A substantial number of people are adopting IWMglobally (Fig. 2).
In crux, weed management is a multi-dimensional regime andcannot be achieved by focusing on a single approach.
Figure 1. Components of integrated weed management in conservation agriculture.
A.A. Bajwa / Crop Protection 65 (2014) 105e113 111
Comprehensive integration of multiple techniques and modifiedtools is necessary to sustain system productivity. It offers long termmanagement, system sustainability, food security and environ-mental safety. So, the integration of weed management options ispromising in CA.
4. Conclusion and future scenario
Modern agriculture is dependent on sustainable food produc-tion regimes and CA is the best system ensuring sustainability andenvironmental safety simultaneously. Its adoption is increasing butweed control is a major challenge. Multiple approaches have beendeveloped to manage weeds but changing attributes under CAmake things complex. Weed infestation, distribution, diversity,growing patterns and resistance levels have been changed underCA. integration of cultural, mechanical, biological, ecological andchemical weed control methods, is judicious under CA. Researchwork is required to link the changing attributes of weeds andmanagement options. Allelopathy, crop nutrition and biologicalweed control may be the effective modernweedmanagement toolsfor CA. However, integration of existing strategies and developmentof new techniques is required. Weed management tools must becombined keeping ecological, geographic, climatic and agronomicaspects of a cropping system in mind. Sincere and devoted en-deavors should be embarked upon to resolve this conundrum. Inthe long run, it will sustain the productivity of CA and, thus, globalfood security.
Figure 2. Adoption of Integrated weed management Source: Llewellyn et al. (2004).
Acknowledgment
Author acknowledges the financial support from Higher Edu-cation Commission (HEC) Pakistan.
References
Abdul-Baki, A.A., Teasdale, J.R., 1993. A no-tillage tomato production system usinghairy vetch and subterranean clover mulches. Hort. Sci. 28, 106e108.
Arif, M., Munsif, F., Waqas, M., Khalil, I.A., Ali, K., 2007. Effect of tillage on weeds andeconomics of fodder maize production. Pak. J. Weed. Sci. Res. 13, 167e175.
Awan, I.U., Khan, M.A., Zareef, M., Khan, E.A., 2009. Weed management in sunflowerwith allelopathic water extracts and reduced doses of a herbicide. Pak. J. Weed.Sci. Res. 15, 19e30.
Azmi, M., 2003. Control of resistant biotype of Limnocharis flava in direct seededrice. In: 6th International Conference on Plant Protection in the Tropics, p. 52.August 11e14, Kuala Lumpur, Malaysia.
Bajwa, A.A., Khalid, S., Sadia, S., Nabeel, M., Nafees, W., 2013. Influence of combi-nations of allelopathic water extracts of different plants on wheat and wild oat.Pak. J. Weed Sci. Res. 19, 157e166.
Ball, D.A., 1992. Weed seed bank response to tillage, herbicide, and crop rotationsequence. Weed Sci. 40, 654e659.
Baudron, F., Andersson, J.A., Corbeels, M., Giller, K.E., 2012. Failing to Yield? Ploughs,conservation agriculture and the problem of agricultural intensification: anexample from the Zambezi Valley. J. Dev. Stud. 48, 393e412.
Beckie, H.J., Hall, L.M., Tardif, F.J., 2001. Herbicide resistance in Canada-where are wetoday? In: Blackshaw, R.E., Hall, L.M. (Eds.), Integrated Weed Management:Explore the Potential. Expert Committee on Weeds, Sainte-Anne-de-Bellevue,Quebec H9 � 3R9, Canada, pp. 1e36.
Behrens, M.R., Mutlu, N., Chakraborty, S., Dumitru, R., Jiang, W.Z., Lavallee, B.J.,Herman, P.L., Clemente, T.E., Weeks, D.P., 2007. Dicamba resistance: enlargingand reserving biotechnology-based weed management strategies. Science 316,1185e1188.
Bhadoria, P.B.S., 2011. Allelopathy: a natural way towards weed management. Am. J.Exp. Agric. 1, 7e20.
Blackshaw, R.E., Brandt, R.N., 2008. Nitrogen fertilizer rate effects on Weedcompetitiveness is species dependent. Weed Sci. 56, 743e747.
Blackshaw, R.E., Larney, F.J., Lindwall, C.W., Watson, P.R., Derksen, D.A., 2001. Tillageintensity and crop rotation affect weed community dynamics in a winter wheatcropping System. Can. J. Plant Sci. 81, 805e813.
Bolliger, A., Magid, J., Amado, T.J.C., Neto, F.S., Ribeiro, M.D.D., Calegari, A., Ralisch, R.,de Neergaard, A., 2006. Taking stock of the Brazilian ‘‘zero-till revolution’’: areview of landmark research and farmers' practice. Adv. Agron. 91, 47e110.
Brar, L.S., 2002. Current status of herbicide resistance in Punjab and its managementstrategies. In: Proc, International Workshop on Herbicide Resistance Manage-ment and Zero Tillage in RiceeWheat Cropping System, pp. 6e10.
Buhler, D., Liebman, M., Obrycki, J., 2000. Theoretical and practical challenges to anIPM approach to weed management. Weed Sci. 48, 274e280.
Buhler, D.D., Stoltenberg, D.E., Becker, R.L., Gunsolus, J.L., 1994. Perennial weedpopulations after 14 years of variable tillage and cropping practices. Weed Sci.42, 205e209.
Bullied, W.J., Marginet, A.M., Van Acker, R.C., 2003. Conventional- and conservation-tillage systems influence emergence periodicity of annual weed species incanola. Weed Sci. 51, 886e897.
Campiglia, E., Paolini, R., Colla, G., Mancinelli, R., 2009. The effects of cover croppingon yield and weed control of potato in a transitional system. Field Crops Res.112, 16e23.
Carter, M., 1994. Strategies to overcome impediments to adoption of conservationtillage. In: Carter, M.R. (Ed.), Conservation Tillage in Temperate Agroecosystems.Lewis Publishers, Boca Raton, pp. 3e19.
Charudattan, R., 2001. Biological control of weeds by means of plant pathogens:significance for integrated weed management in modern agro-ecology.Biocontrol 46, 229e260.
Chaudhry, O., 2008. Herbicide-resistance and Weed-Resistance Management. Al-bert Campbell Collegiate Institute, Toronto, Ontario, Canada.
Chauhan, B.S., Mahajan, G., 2012. Role of integrated weed management strategies insustaining conservation agriculture systems. Curr. Sci. 103, 135e136.
Chauhan, B.S., Gill, G.S., Preston, C., 2006a. Influence of tillage systems on verticaldistribution, seedling recruitment and persistence of rigid ryegrass (Loliumrigidum). Weed Sci. 54, 669e676.
Chauhan, B.S., Gill, G.S., Preston, C., 2006b. Tillage systems affect trifluralinbioavailability in soil. Weed Sci. 54, 941e947.
Chauhan, B.S., Gill, G.S., Preston, C., 2007. Effect of seeding systems and dini-troaniline herbicides on emergence and control of rigid ryegrass (Lolium rig-idum) in wheat. Weed Technol. 21, 53e58.
Cheema, Z.A., Khaliq, A., 2000. Use of sorghum allelopathic properties to controlweeds in irrigated wheat in semi-arid region of Punjab. Agric. Ecosyst. Environ.79, 105e112.
Cheema, Z.A., Khaliq, A., Tariq, M., 2002. Evaluation of concentrated sorghum waterextract alone and in combination with reduced rates of three pre-emergenceherbicides for weed control in cotton (Gossypium hirsutum L.). Int. J. Agric.Biol. 4, 549e552.
A.A. Bajwa / Crop Protection 65 (2014) 105e113112
Clements, D.R., Benoit, D.L., Murphy, S.D., Swanton, C.J., 1996. Tillage effects onweedseed return and seed bank composition. Weed Sci. 44, 314e322.
Creamer, N.G., Plassman, B., Bennett, M.A., Wood, R.K., Stinner, B.R., Cardina, J., 1995.A method for mechanically killing cover crops to optimize weed suppression.Am. J. Alt. Agric. 10, 157e162.
Curran, W.S., Lingenfelter, D.D., Garling, L., 1996. Weed management in Conserva-tion Tillage. In: Conservation Tillage Fact Sheet Series. Penn State College ofAgric. Sci., Univ. Park, PA.
Cussans, G.W., 1976. The influence of changing husbandry on weeds and weedcontrol in arable crops. In: Proc. Brit. Crop Prot. Conf. Weeds, Brighton, UK,pp. 1001e1008.
Davis, A., Renner, K., Sprague, C., Dyer, L., Mutch, D., 2005. Integrated Weed Man-agement: One Year's Seeding. East Lansing: Michigan State University. Exten-sion Bulletin. E-2931.
De Witt, T.C., Vickery, C., Heier, J., 2002. Control of herbicide resistant watergrass innorthern California rice with bispyribac sodium 80 WP herbicide. In: Hill, J.E.,Hardy, B. (Eds.), Second Temperate Rice Conference. International Rice ResearchInstitute, Los Banos, Philippines, pp. 638e639.
Derksen, D.A., Blackshaw, R.E., Boyetchko, S.M., 1996. Sustainability, conservationtillage and weeds in Canada. Can. J. Plant Sci. 76, 651e659.
Derpsch, R., 2003. Conservation tillage, no-tillage and related technologies. Conserv.Agric. Environ. Farm. Exp. Innov. Socio-Econ. Policy, 181e190.
Edwards, W., Smith, D., 2005. Iowa Custom Farm Rate Survey. Ames: Iowa StateUniversity.
Evans, S.P., Knezevic, S.Z., Shapiro, C., Lindquist, J.L., 2003. Nitrogen level affectscritical period for weed control in corn. Weed Sci. 51, 408e417.
FAO, 2001. Summary, Conservation Agriculture, Matching Production with Sus-taiablility. Available at: http://www.fao.org/ag/ags/agse/agse e/general/OBJECT.htm. last checked on 03.04.13.
Farooq, M., Bajwa, A.A., Cheema, S.A., Cheema, Z.A., 2013. Application of allelopathyin crop production. Int. J. Agric. Biol. 15, 1367e1378.
Farooq, M., Flower, K.C., Jabran, K., Wahid, A., Siddique, K.H.M., 2011b. Crop yieldand weed management in rainfed conservation agriculture. Soil Till. Res. 117,172e183.
Farooq, M., Jabran, K., Cheema, Z.A., Wahid, A., Siddique, K.H.M., 2011c. The role ofallelopathy in agricultural pest management. Pest Manag. Sci. 67, 493e506.
Farooq, M., Siddique, K.H.M., Rehman, H., Aziz, T., Lee, D.J., Wahid, A., 2011a. Ricedirect seeding: challenges and opportunities. Soil Till. Res. 111, 87e98.
Fowler, R., Rockstrom, J., 2001. Conservation tillage for sustainable agriculture-anagrarian revolution gathers momentum in Africa. Soil Till. Res. 61, 93e107.
Gealy, D.R., Mitten, D.H., Rutger, J.N., 2003. Gene flow between red rice (Oryza sativaL.) and herbicide-resistant rice (Oryza sativa): implications for weed manage-ment. Weed Technol. 17, 627e645.
Giller, K.E., Witter, E., Corbllels, M., Tittonell, P., 2009. Conservation agriculture andsmallholder farming in Africa: the heritics view. Field Crops Res. 114, 23e34.
Givens, W.A., Shaw, D.R., Kruger, G.R., Johnson, W.G., Weller, S.C., Young, B.G.,Wilson, R.G., Owen, M.D.K., Jordan, D., 2009. Survey of tillage trends followingthe adoption of glyphosate-resistant crops. Weed Technol. 23, 150e155.
Green, J.M., 2011. Outlook on weed management in herbicide-resistant crops: needfor diversification. Outlooks Pest Manag. 22, 100e104.
Hartzler, R.G., Owen, M.D., 1997. Weed Management in Conservation Tillage Sys-tems. Ames: Iowa State University, University Extension.
Hillel, D., 1991. Out of the Earth: Civilization and the Life of the Soil. Free Press, NewYork, NY.
Hillel, D., 1998. Environmental Soil Physics. Academic Press, San Diego, CA.Hobbs, P.R., 2007. Conservation agriculture: what is it and why is it important for
future sustainable food production? J. Agric. Sci. 145, 127e137.Hobbs, P.R., Sayre, K., Gupta, R., 2008. The role of conservation agriculture in sus-
tainable agriculture. Proc. Philos. Trans. R. Soc. B. Biol. Sci. 363, 543e555.Holland, J.M., 2004. The environmental consequences of adopting conservation
tillage in Europe: reviewing the evidence. Agric. Ecosyst. Environ. 103, 1e25.Iqbal, J., Cheema, Z.A., An, M., 2007. Intercropping of field crops in cotton for the
management of purple nutsedge (Cyperus rotundus L.). Plant Soil 300, 163e171.Iqbal, J., Cheema, Z.A., Mushtaq, M.N., 2009. Allelopathic crop water extracts reduce
the herbicide dose for weed control in cotton (Gossypium hirsutum). Int. J. Agric.Biol. 11, 360e366.
Jabran, K., Cheema, Z.A., Farooq, M., Basra, S.M.A., Hussain, M., Rehman, H., 2008.Tank mixing of allelopathic crop water extracts with pendimethalin helps in themanagement of weeds in canola (Brassica napus) field. Int. J. Agric. Biol. 10,293e296.
James, C., 2010. Global status of commercialized Biotech/GM crops. In: The Inter-national Service for the Acquisition of Agri-biotech Applications Brief No. 42.ISAAA, Ithaca, NY.
Khalid, S., Ahmad, T., Shad, R.A., 2002. Use of allelopathy in agriculture. Asian J.Plant Sci. 1, 292e297.
Khaliq, A., Matloob, A., Irshad, M.S., Tanveer, A., Zamir, M.S.I., 2010. Organic weedmanagement in maize (Zea mays L.) through integration of allelopathic cropresidues. Pak. J. Weed Sci. Res. 16, 409e420.
Kim, S.C., Ha, W.G., 2005. Direct seeding and weed management in Korea. In:Toriyama, K., Heong, K.L., Hardy, B. (Eds.), Rice is Life: Scientific Perspectives forthe 21st Century. International Rice Research Institute, Los Banos, Philippines,and Japan International Research Center for Agricultural Sciences (Tsukuba,Japan. CD).
Labrada, R., Parker, C., 1994. Weed control in the context of integrated pest man-agement, weed management for developing countries. In: Labrada, R.,
Caseley, J.C., Parker, C. (Eds.), Plant Production and Protection Paper No. 120,FAO, pp. 3e8. Rome.
Lafond, G.P., McConkey, B.G., Stumborg, M., 2009. Conservation tillage models forsmall-scale farming: linking the Canadian experience to the small farms ofinner Mongolia autonomous region in China. Soil Till. Res. 104, 150e155.
Lal, R., 2000. Soil management in the developing countries. Soil Sci. 165, 57e72.Lal, R., 2001. Managing world soils for food security and environmental quality. Adv.
Agron. 74, 55e192.Lanini, W.T., Pittenger, D.R., Graves, W.L., Munoz, F., Agamalian, H.S., 1989. Subc-
lovers as living mulches for managing weeds in Vegetables. Calif. Agric. 43,25e27.
Lindsey, L.E., Darryl, D., Warncke, K.S., Wesley, J.E., 2013. Fertilizer and populationaffects nitrogen assimilation of common lambsquarters (Chenopodium album)and redroot pigweed (Amaranthus retroflexus). Weed Sci. 61, 131e135.
Llewellyn, R.S., Lindner, R.K., Pannell, D.J., Powles, S.B., 2004. Grain grower per-ceptions and use of integrated weed management. Anim. Prod. Sci. 44,993e1001.
Lyon, D., Bruce, S., Vyn, T., Peterson, G., 2004. Achievements and future challengesin conservation tillage. In: Proceedings of the 4th International Crop ScienceCongress, 26 Sepe1 Oct, Brisbane, Australia.
Makus, D.J., Tiwari, S.C., Pearson, H.A., Haywood, J.D., Tiarks, A.E., 1994. Okra pro-duction with pine straw mulch. Agrofor. Syst. 27, 121e127.
Marambe, B., Amarasinghe, L., 2002. Propanil resistant barnyardgrass (Echinochloacrusgalli (L.) Beauv.) in Sri Lanka: seedling growth under diVerent temperaturesand control. Weed Biol. Manag. 2, 194e199.
Montgomery, D.R., 2007. Soil erosion and agricultural sustainability. Proc. Natl.Acad. Sci. U. S. A. 104, 13268e13272.
Moss, S., 1997. Strategies for the prevention and control of herbicide resistance inannual grass weeds. In: DePrado, R., Jorrin, J., Garcia-Torres, L. (Eds.), Weed andCrop Resistance to Herbicides. Kluwer Academic Publishers, Dordrecht, TheNetherlands, pp. 283e290.
Müller-Sch€arer, H., Scheepens, P.C., Greaves, M.P., 2000. Biological control of weedsin European crops: recent achievements and future work. Weed Res. 40, 83e98.
Nagabhushana, G.G., Worsham, A.D., Yenish, J.P., 2001. Allelopathic cover crops toreduce herbicide use in sustainable agricultural systems. Allelopath. J. 8,133e146.
Nazir, S., 1994. Crop Production, first ed. National book foundation, Islamabad.Owen, M.D.K., Zelaya, I., 2004. Herbicide-resistant crops and weed resistance to
herbicides. Pest Manag. Sci. 61, 301e311.Owen, M.J., Walsh, M.J., Llewellyn, R.S., Powles, R.S., 2007. Wide spread occurrence
of multiple herbicide resistance in Western Australian annual ryegrass (Loliumrigidum) populations. Aust. J. Agric. Res. 58, 711e718.
Owens, H., 2001. Tillage: From Plow to Chisel and no-tillage.1930e1999. MidwestPlan Service. Ames: Iowa State University.
Pannell, D.J., 1990. Responses to risk in weed control decisions under expectedprofit maximization. J. Agric. Econ. 41, 391e404.
Phillips, S.H., Young, H.J., 1973. No-tillage Farming. Reiman Associates, Milwaukee.Pollard, F.S., Moss, R., Cussans, G.W., Froud-Williams, R.J., 1982. The influence of
tillage on the weed flora in a succession of winter wheat crops on a clay loamsoil and silt loam soil. Weed Res. 22, 129e136.
Powles, S., Matthews, J., 1991. Multiple herbicide resistance in annual ryegrass: adriving force for the adoption of integrated weed management. In: Denholm, I.,Devonshire, A., Hollomon, D. (Eds.), Resistance 91: Achievements and De-velopments in Combating Pesticide Resistance. Elsevier, London, pp. 75e87.
Pratley, J.E., Flower, R., Heylin, E., Sivapalan, S., 2004. Integrated Weed ManagementStrategies for the Rice Weeds Cyperus Diformis and Alisma Plantago Aquatica.RIRDC Publication No. 04/008. RIRDC Project No. UCS 20A. Rural IndustriesResearch and Development Corporation, Australia.
Rao, A.N., Johnson, D.E., Sivaprasad, B., Ladha, J.K., Mortimer, A.M., 2007. Weedmanagement in direct-seeded rice. Adv. Agron. 93, 153e255.
Reicosky, D.C., Allmaras, R.R., 2003. Advances in tillage research in North Americancropping systems. J. Crop Prod. 8, 75e125.
Scherder, E.F., Talbert, R.E., Lovelace, M.L., Buehring, N.W., 2001. Weed controlprograms in herbicide tolerant rice. Proc. South Weed Sci. Soc. 54, 39e40.
Sherestha, A., Lanini, T., Wright, S., Vargas, R., Mitchle, J., 2006. Publication 8200available on the ANR communication services (online). Available at: http://anrcatalog.ucdavis,edu. last checked on 07.05.13.
Shrestha, A., Vargas, R., Mitchell, J., Cordova, D., 2003. Initial experiences in tran-sition from conventional to conservation tillage: a farming systems perspective.In: Proc. Conservation Tillage: the California Experience. Oct. 7e9, Tulare, FivePoints, Davis, California.
Singh, H.P., Batish, D.R., Kohli, R.K., 2003. Allelopathic interactions and alle-lochemicals: new possibilities for sustainable Weed management. Crit. Rev.Plant Sci. 22, 239e311.
Sosnoskie, L.M., Herms, N.P., Cardina, J., 2006. Weed seed bank communitycomposition in a 35-yr-old tillage and rotation experiment. Weed Sci. 54,263e273.
Swanton, C.J., Weise, S.F., 1991. Integrated weed management: the rationale andapproach. Weed Technol. 5, 657e663.
Sweeney, A.E., Renner, K.A., Laboski, C., Davis, A., 2008. Effect of fertilizer nitrogenon weed emergence and growth. Weed Sci. 56, 714e721.
Teasdale, J.R., Mohler, C.L., 2000. The quantitative relationship between weedemergence and the physical properties of mulches. Weed Sci. 48, 385e392.
Triplett, G.B., Warren, A.D., 2008. No-tillage crop production: a revolution in agri-culture. Agron. J. 100, 151e165.
A.A. Bajwa / Crop Protection 65 (2014) 105e113 113
Valverde, B.E., Chaves, L., Garita, I., Ramfirez, F., Vargas, E., Carmiol, J., Riches, C.R.,Caseley, J.C., 2001. Modified herbicide regimes for propanil resistant junglegrass control in rainfed rice. Weed Sci. 49, 395e405.
Vargas, R.N., Wright, S.D., 2005. UC IPM Pest Management Guidelines: Cotton.Statewide IPM Program. Division of Agriculture and Natural Resources, Uni-versity of California Publication 3444, Oakland.
Wallace, R.W., Bellinder, R.R., 1992. Alternative tillage and herbicide options forsuccessful weed control in vegetables. Hort. Sci. 27, 745e749.
Watson, A.K., 1991. The classical approach with plant pathogens. In: TeBeest, D.O.(Ed.), Microbial Control of Weeds. Chapman and Hall, New York, pp. 3e23.
Wazir, I., Sadiq, M., Baloch, M.S., Awan, I.U., Khan, E.A., Shah, I.H., Nadim, M.A.,Khakwani, A.A., Bakhsh, I., 2011. Application of bio-herbicide alternatives forchemical weed control in rice. Pak. J. Weed Sci. Res. 17, 245e252.
Weaver, S.E., Kropff, M.J., Groeneveld, R.M.W., 1992. Use of ecophysiological modelsfor crop-weed interference: the critical period of weed interference. Weed Sci.40, 302e307.
Wrucke, M.A., Arnold, W.E., 1985. Weed species distribution as influenced by tillageand herbicides. Weed Sci. 33, 853e856.
