herbicide resistance - Grains Research & Development Corporation

The need to learn to lovethe herbicides we haveIntroduction2By Dr Ken YoungHerbicide-resistant weedsrepresent the single largest threat to Australianand global food security – and cost Australiangrowers more than $200 million every year.However, along with having the second largestherbicide resistance problem in the world (we wererecently knocked out of first place by the US),Australia is also a world-leader in managing herbicideresistantweeds. Necessity and targeted research,development and extension investment have bredimpressive and world-renowned success in developingintegrated approaches to weed management.Innovations such as the GRDC-funded HarringtonSeed Destructor (HSD), which can remove up to 95 percent of weed seed in the harvested chaff fraction, are setto have a significant impact on reducing the effect ofGround Cover is brought to you by growers and the Australian Government through thepublisher, the Grains Research and Development Corporation (GRDC).GRDC: 02 6166 4500, fax 02 6166 4599Write to: The Editor – Ground Cover, PO Box 5367, Kingston ACT 2604Publishing Manager: Ms Maureen Cribb, GRDC, 02 6166 4500Coretext: 03 9670 1168, fax 03 9670 1127, editor@coretext.com.au, www.coretext.com.auManaging editor: Brad CollisEditor: Janet PatersonProduction editor: Victoria AmyAdvertising sales: Max Hyde, Hyde Media Pty Ltd, 03 5792 1314,fax 03 5792 1359, max@hydemedia.com.auAdvertising is subject to terms and conditions published on the rate card,available from Hyde Media, and on the website www.coretext.com.auCirculation: Ms Maureen Cribb, 02 6166 4500 Printing: Cadillac Printing, AdelaideISSN 1039-6217 Registered by Australia Post Publication No. NAD 3994Disclaimer: This publication has been prepared in good faith by the GRDC on the basisof the information available to us at the date of publication, without any independentverification. Neither the GRDC and its editors nor any contributor to this publicationrepresent that the contents of this publication are accurate or complete; nor do we acceptany responsibility for any errors or omissions in the contents, however they may arise.Readers who act on information from Ground Cover supplement do so at their own risk.The GRDC and contributors to Ground Cover supplement may identify products byproprietary or trade names to help readers identify particular types of products. We do notendorse or recommend the products of any manufacturer referred to. Other products mayperform as well as or better than those specifically referred to.CAUTION: RESEARCH ON UNREGISTERED PESTICIDE USEAny research with unregistered pesticides or of unregistered products reported in thisdocument does not constitute a recommendation for that particular use by the authors orthe authors’ organisations.Copyright: © All material published in the Ground Cover supplement series is copyrightprotected and may not be reproduced in any form without written permission from the GRDC.All pesticide applications must accord with the currently registered label for thatparticular pesticide, crop, pest and region.Ground Cover Supplement edited by Janet Patersonweeds and herbicide resistance in our cropping systems.Developed initially by Western Australian inventor andgrower Ray Harrington, with GRDC funding the HSDhas recently been fully integrated into a class 9 headerand will become widely used within the next few years.The GRDC’s investment in herbicide resistanceRD&E is channelled through the Australian HerbicideResistance Initiative (AHRI), which is based in Perthand directed by a world leader in herbicide resistanceresearch, Professor Stephen Powles. Through AHRI,integrated management systems for each of Australia’sgrowing regions have been developed and testedand the genetic mechanisms through which weedsoutsmart herbicides are continuing to be unravelled.With six weed species now confirmed to haveglyphosate-resistant populations across Australiancropping systems, the work of the GRDC-supportedAustralian Glyphosate Sustainability Working Groupis more important than ever. The group’s nationaltraining work in integrated weed management is helpingto prolong the life of our most valuable knockdownherbicide, better understand how weeds become resistantto its chemistry, and monitor and better manage therisk of glyphosate resistance spreading further.Australian cropping systems rely on herbicideswith only six modes of action and the likelihoodof herbicides with different chemistries becomingavailable in the near future is very low. ProfessorPowles says: “We need to learn to love the herbicideswe’ve got”. This means implementing chemicaland non-chemical practices that curb herbicideresistance developing in weed populations.The GRDC, with government, university andcommercial partners, has launched a website (www.weedsmart.org.au) – a first-point-of-call website wheregrowers and advisers can access the latest informationon sustainable herbicide use in Australian agriculture.This Ground Cover supplement outlinesways to make our limited herbicides last aslong as possible so that our cropping systemscontinue to be productive and viable. □More information: Dr Ken Young,GRDC, 02 6166 4500, ken.young@grdc.com.auCover photo: Evan CollisDr Roberto Busi sprays weed seedlings with herbicide at theAustralian Herbicide Resistance Initiative in Western Australia.

Glyphosate lostto the USThe results of over-reliance on glyphosate in GM crops inthe US has driven home the unavoidable truth that herbicideresistance cannot be managed with herbicides aloneUniversity of Arkansas weed scientist Dr JasonNorsworthy (pictured) says glyphosate is now lost tothe US after widespread overuse of the herbicide inGM cropping systems. Glyphosate-resistant weedssuch as the Palmer amaranth pictured are nowendemic on 50 per cent of US farming properties.3Herbicide resistance – global viewBy Janet PatersonThirty years ago, herbicideresistantweeds were a mere academiccuriosity, herbicides dominated weedcontrol (and always worked well) andGM stood for General Motors.The present reality is that weedshave evolved resistance to 21 of the25 known herbicide modes of actionthat underpin 148 different herbicides.Herbicide-resistant weeds have now beenreported in 63 crops in 61 countries.In another significant shift, GMis now intimately associated with‘glyphosate-resistant’ soy, cotton, maizeand canola, which in the US and Canadahas become the most rapidly adoptedtechnology in the history of agriculture.Glyphosate-resistant weeds nowdominate herbicide resistance research,with 24 species across 18 countriesreported as resistant to glyphosate.No longer an academic curiosity,herbicide-resistant weeds represent a majorannual threat to crop production, profitabilityand sustainability across the globe.Glyphosate lost to the USA recent US and Canadian surveyrevealed that almost half of all growersin these countries suspect they haveglyphosate-resistant weeds in theirGM cropping systems. In the US, 25million hectares – about the total areaof cropping in Australia – is infestedwith glyphosate-resistant weeds.The biggest weed problem in the US isPalmer amaranth, a succulent that emergesover seven months, grows at a rate of threeto 10 centimetres per day and generatesone million seeds per plant. GlyphosateresistantPalmer amaranth is now in 26US states and is spreading at a fast rate.In Argentina, glyphosate-resistant Johnsongrass is also a rapidly growing issue.Many now believe glyphosate is lost tothe US, with Argentina and Brazil likelyto suffer the same fate given their highadoption of glyphosate-resistant crops.In an ironic twist, some US growershave had to resort to the age-old practiceof hand-weeding and deep tillage tomanage herbicide-resistant crop weeds.In Tennessee, where nearly all growerspractised no-till five years ago, morethan half have now had to return to deeptillage to bury herbicide-resistant weeds.Australia and herbicideresistanceIn Australia, following two to threedecades of reliance on glyphosate forfallow and pre-sowing weed control, fivephoto: Fred Millerweed species have developed glyphosateresistance in the northern growing region,threatening the viability of no-till farming.Glyphosate-resistant ryegrass is alsoemerging as a significant issue alongfencelines, roadsides and train tracks acrossAustralia, which have for many yearsbeen controlled using glyphosate. Thereis a risk that these resistant weeds couldjump the fence into cropping paddocks.Multiple resistance to in-cropherbicides is now the norm in annualryegrass and wild radish populationsin Western Australia and increasinglyacross southern Australia after decadesof herbicide use in continuouscropping,minimum-tillage systems.How did we get here?It may seem like stating the obvious, butit seems we often forget that herbicideresistance is inevitable when herbicidesalone are used to control weeds.Before the introduction of GM soybeansin the US, 19 different herbicides werebeing used on soybean crops. Followingthe widespread adoption of glyphosateresistantsoybeans, fewer than five percent of soybean growers continued touse a herbicide other than glyphosateto control weeds. Over-reliance onglyphosate alone has also been the norm

Herbicide resistance – global view4photo: Dr Jason Norsworthyfor GM corn, canola and cotton.Before minimum tillage andcontinuous cropping became standardin the northern wa wheatbelt, weedswere controlled with cultivation, sheepand herbicides. Following the moveto no-tillage and permanent cropping,in-crop selective herbicides became thepredominant form of weed control.Weeds have an inherent capacity(developed over millions of years) todevelop resistance mechanisms to attackand will even develop ways to combatmechanical control if the method is usedconsistently for a long enough period.The only way to extend the life of anyherbicide and play weeds at their ownresistance game is to use a range ofchemical and non-chemical methods,such as rotating herbicides, harvest weedseed control and growing competitivecrops, to fully control weed populations.If weed densities are kept low, then thelikelihood of resistance genes evolvingwithin the population is also kept low,and herbicide usefulness is extended.Chemical controlHerbicide resistance would not be aproblem if new, effective herbicidesbecame available as old herbicidesbecame redundant. We could justkeep replacing old chemistries withnew ones to control weeds.But it is extremely unlikely thatnew modes of herbicide action willbecome available in the near future.Also, European regulators are forcing theremoval of some chemistries, reducingthe number of herbicides at our disposal.It is therefore critical that we extend thelife of herbicides for as long as possible.GlyphosateresistantPalmeramaranth hasbecome sowidespread inUS soybeanand cottoncrops thatmany growershave hadto resort tohand-weedingcrops toremoveresistantweeds.The US has learnt the hard way thatover-reliance on one herbicide (and onecropping system) for weed control canlead to a disastrous situation for cropproduction. A recent survey of US growersshowed that, disturbingly, many stillexpect a silver (chemical) bullet to bedeveloped to replace glyphosate. This isunderstandable given that glyphosate itselfbecame available during the ‘golden age’of herbicide discovery in the 1970s and at atime when resistance to selective herbicideshad become almost unmanageable.No new discoveriesBut the reality is that there are no newmodes of herbicide action on the horizon.The previous new herbicide mode ofaction was developed more than 30 yearsago, and since then there has been an 80per cent drop in the number of companiesactively pursuing new chemistries.Herbicide development is expensive– about $250 million from discoveryto commercialisation – and with themarket largely captured by glyphosateresistantcrops, new herbicidediscoveries just have not been a viablebusiness activity in the short term.The over-reliance on glyphosate inGM cropping systems, extensive presenceof glyphosate-resistant weeds and thelack of new herbicides on the horizonhave combined to bring the US croppingsystem to a tipping point. While GMcrops with multiple stacked-resistancegenes will buy time, they are not the longtermanswer to herbicide resistance.Herbicide resistance will not besolved with herbicides. Only integratedweed management and a zero tolerancefor weed escapes will enable long-termcontrol of resistant weed populations.Managing resistance forfood securityAccording to the father of the GreenRevolution, Norman Borlaug, theworld will need to produce morefood in the next 50 years than it hasproduced in the past 10,000 years.Herbicide resistance represents a majorthreat to world food security. How wemanage it will determine our capacityto rise to this food security challenge.Australia can learn from the USexperience with glyphosate resistanceand profit from extending the life ofthis valuable knockdown herbicide.Like the US, our over-reliance on singleherbicide modes of action and a lack ofdiversity in our cropping systems have ledto significant herbicide resistance issues.We are second only to the US in ournumber of herbicide-resistant weed species.Thankfully, glyphosate remains effectiveagainst most of our cropping weeds, butlosing it to widespread resistance wouldbe a disaster for pre-sowing and fallowweed control. Extending its useful life isdependent on integrated weed management.Unlike the US, Australia has respondedto its herbicide resistance problem notby expecting a new chemical solutionbut by developing innovative nonchemicalweed control measures.Necessity has bred invention with thedevelopment of several harvest weed-seedsystems – from chaff carts through to thenewly released Harrington Seed Destructor– all of which have the capacity to reduceweed populations to almost zero whenused properly. In some instances, growerswith a significant herbicide resistanceproblem have been able to reduce their weedseedbanks so significantly that they can nowdry-seed with confidence and sometimeshave no need for in-crop weed control.Targeting weed seeds at harvest isnow a major focus of grain producersin wa and increasingly in southernAustralia. The majority of these growersare optimistic about the future of graincropping in their regions, despite highlevels of herbicide-resistant weeds.We will benefit from exporting ourexpertise in these systems to countriessuch as the US, Canada, Argentina andBrazil as they face the challenging futureof increasing herbicide resistance andfewer chemical weed-control options. □GRDC Research Code UWA00146More information: Professor StephenPowles, 08 6488 7833,stephen.powles@uwa.edu.au

Resistance rising across AustraliaAustralia has the second highest number of herbicide-resistant weeds in the world –sitting only just behind the US. Twenty-five weed species have been confirmed resistantto one or more herbicides across Australia’s cropping regionsBy Mechelle Owen, Dr Chris Prestonand Associate Professor Steve WalkerHerbicide-resistant weeds areon the rise across Australia, includingan increasing number of cropping weedswith resistance to multiple herbicides.Western regionIn Western Australia, multiple resistanceis now the norm for the state’s twoworst cropping weeds – annual ryegrassand wild radish. Only two per cent ofannual ryegrass populations remainfully susceptible to herbicide control,with all others resistant to one ormore herbicide modes of action.Fortunately atrazine, paraquat andglyphosate continue to provide good controlon most annual ryegrass populations inwa, except for some populations across thesouthern coastal growing area (Figure 1).A similar story exists for wild radish,with 93 per cent of populations resistantto one or more herbicides. A recentsurvey by the Australian HerbicideResistance Initiative (AHRI) found that84 per cent of 96 wild radish populationstested from Geraldton in the north toEsperance in the south had some levelof resistance to the Group B herbicidechlorsulfuron (Glean ® ). Other herbicidessuch as glyphosate, atrazine and Velocity ®(bromoxynil and pyrasulfotole) are stillproviding good control of wild radish.Growers are being urged not to rely onherbicides alone to control cropping weeds.Non-herbicide methods for weed control,such as harvest weed seed control and cropcompetition, are being increasingly adoptedacross the wa wheatbelt and are provinghighly successful at controlling weedsthat escape pre-sowing herbicide control.Southern regionAcross southern Australia, resistance isincreasing in ryegrass and wild radish –mirroring the situation in the west, butlagging a few years behind because of amore diverse farming system. However,with the shift to a more intensive croppingsystem and higher herbicide use, itcould only be a matter of time beforeFIGURE 1 Incidence of multi-resistant wild radish acrossWestern Australian cropping zone.GERALDTONTable 1 Percentage of paddocks with herbicide-resistant annualryegrass in cropping regions of South Australia and Victoria.RegionSA –Mid NorthSA –MalleeSA –South EastSA – EyrePeninsulaVictoria –WesternVictoria –NorthernVictoria –SouthernPERTHYearMullewaMingenewMooraMulti-resistantResistant to one herbicideSusceptible to herbicide resistanceDalwallinuWongan HillsNorthamNarroginKojonupALBANYthe southern cropping states reach waresistance levels. Resistance could bedelayed in the southern region throughadoption of the now widespread and highlysuccessful harvest weed-seed controltechniques used by wa growers to manageMukinbudinSouthern CrossMerredinKondininLake GraceJerramungupESPERANCE260 kilometresTrifluralin Hoegrass ® Glean ® Axial ® Select ® Intervix ®Populations resistant (%)2008 40 76 73 59 40 not tested2007 19 6 67 2 2 not tested2007 39 60 69 53 41 not tested2009 5 30 78 30 11 472010 25 40 73 33 5 182011 0 55 87 31 8 292009 0 79 88 68 23 39065Lake KingRavensthorpeSource: 2013 NSW GRDC Grains Research Update for Advisers130Salmon GumsSOURCE: AUSTRALIAN HERBICIDE RESISTANCE INITIATIVE, 2010 SURVEYherbicide-resistant weed populations.The level of chlorsulfuron (GroupB) herbicide-resistant milkthistle acrosssouthern Australia now matches that of thenorthern cropping region, rendering theweed a national problem in cropping and5Herbicide resistance – Australian view

fallow situations. Fortunately, switchingto other mode-of-action herbicides is aneffective management strategy, but theuniversal distribution of this species andwidespread resistance to Group B herbicidesis a future threat to cropping systems.Annual ryegrassSouth Australian and Victorian surveysshow the incidence of herbicide resistanceis increasing in annual ryegrass populationsin these states (Table 1). Seventy-fiveper cent of paddocks across south-eastAustralia have Group B chlorsulfuronresistantryegrass. A high level of ryegrassresistance to Group D trifluralin exists inSA and is emerging as an issue in Victoria.FIGURE 2 The increase in confirmed cases of glyphosateresistance in summer weeds across Australia, 2007−12.Number of resistant populations604020Clethodim resistanceRyegrass with resistance to the GroupA herbicide clethodim is also increasingacross southern Australia. This isconcerning because there are no highlyeffective alternatives to clethodim forcontrolling annual ryegrass post-emergencein canola and faba beans. With clethodimresistance, the most effective managementmay be to use an effective pre-emergentherbicide coupled with clethodim on youngryegrass plants and follow up by croptopping with glyphosate on faba beans. Anapplication for crop topping canola withglyphosate was submitted to the AustralianPesticides and Veterinary MedicinesAuthority (AVPMA) in September 2012.FleabaneGlyphosate resistanceGlyphosate-resistant weeds are on the riseacross Australia, with six species now confirmedwith resistant populations – annual ryegrass,barnyard grass, liverseed grass, windmill grass,brome grass and fleabane (see Figures 2 and3). Weeds with resistance to glyphosate havebeen found in every mainland Australian state.There are 347 documented glyphosate-resistantpopulations of annual ryegrass across Australia.Of these cases, nearly half come from roadsideverges and cropping fencelines – reflecting thelong-term use of glyphosate to control weeds onproperty firebreaks and council verges. Australiahas 612,000 kilometres of road consideredat risk of developing weeds with glyphosateresistance, so the potential problem is huge. Inaddition, market research has found many landmanagers are poorly prepared to deal with thelooming crisis. The majority of the remainingcases stem from long-term use of glyphosatein broadacre cropping systems, particularlysummer fallows. Glyphosate is an excellentherbicide that helps keep management costsdown, but there are no easy replacementoptions available. The rapid developmentof glyphosate-resistant weeds and species’shift to glyphosate-tolerant status will have alarge impact on the cost and ease of weedmanagement in Australian cropping systems. Itis critical that the life of this valuable herbicide isextended via integrated weed management.Herbicide resistance – Australian view0FIGURE 3 The increase in confirmed cases of glyphosateresistantannual ryegrass across Australia, 1996−2012.Number of resistant populations400300200100Barnyard grassLiverseed grassWindmill grass2006 2007 2008 2009 2010 2011 2012YearWild radishHerbicide-resistant wild radish is becominga serious threat across the southern region,with more than 20 paddocks across Victoriaand SA being reported to have populationswith resistance. Of these, five populationsare resistant to Group I herbicides (threein Victoria and two in SA) and one isresistant to Group B, Group F and Group I.Since 2009, half of the 60 wild radishsamples received for annual herbicideresistancetesting from growers acrosssouth-east Australia have been verified asresistant to Group B and Group I herbicides.Northern regionGlyphosate-resistant weeds in chemicalfallows are threatening the viability ofno-till cropping systems in the northerncropping region. Resistant annual ryegrass,barnyard grass and flaxleaf fleabane topthe list. Glyphosate-resistant windmillgrass, and to a lesser extent liverseed grass,are also increasingly being reported.601996 2000 2004 2008 2012YearGRDC Research Code UWA00146More information: Chris Preston, 08 8313SOURCE: AUSTRALIAN GLYPHOSATE SUSTAINABILITY WORKING GROUP7237, christopher.preston@adelaide.edu.au

Lift sowing to outcompete weedsThere is a widespread belief that lifting sowing rates results in increased screenings,but GrdC-funded research in Western Australia shows higher crop densities can significantlylower weed burdens without any impact on wheat quality7By Peter Newman and Christine ZaicouCrop coMPetition is the unsunghero of herbicide resistance management.Department of Agriculture and Food,Western Australia (DAFWA) research in thenorthern wa wheatbelt shows that increasingthe wheat sowing rate can decrease seed-setof annual ryegrass by nearly 80 per cent.In addition to outcompetingryegrass, increasing the wheat densitylifted the efficacy of the pre-emergentherbicide Sakura ® from a 95 to 99 percent seed-set reduction of ryegrass.The concept of crop competition inweed management is not new, but inrecent years many growers in southernAustralia have inadvertently underminedthe competitive capacity of their crops byincreasing row spacing, lowering sowingrates and sowing uncompetitive cultivars.While the shift to wider rows and lowersowing densities has been based on validreasoning, the question remains of howmuch these practices are costing growersin terms of crop yield and weed control.With widespread multiple herbicideresistance now the norm in wa, growersneed all the non-herbicide tools available tothem to help control the number of weeds.Lifting density in wide rowsIn the DAFWA research, crop densitywas increased using stiletto bootsto generate paired cropping rows 75millimetres apart, effectively reducingrow spacing by the same amount withouthaving to add extra tynes to the seeder.Paired-row sowing doubles the lengthof the cropping row without significantlyaffecting row spacing. The paired rows resultin less in-row competition between cropplants than the same sowing density in singlerows, enabling more seeds to germinateand establish at higher sowing rates.Existing sowing machinery can bemodified for paired-row sowing so that thetyne spacing that is best for stubble handlingand sowing speed can remain the same.Even in the absence of a pre-sowinggrass-selective herbicide, ryegrass seedsetwas reduced by as much as 65 percent with an increase in crop densityfrom 40 to 160 kilograms per hectare.Combined with the pre-emergent grassselectiveSakura ® , crop competition wasfurther enhanced and ryegrass seed-setreduced from 811 seeds per square metreat the 40kg/ha sowing rate to 178 seeds/m 2 at the 120kg/ha seed rate (Figure 1).The density research found what manycrop competition trials have repeatedlyshown: as crop density increases, cropbiomass increases and weed growth andseed-set decrease. The challenge is to dothis in a practical and cost-effective way.The stiletto boot system requires only aminor adaptation to existing machineryand the paired rows do not interfere withstubble management or time of operation.The big question surrounds economicsand how viable it is to increase the sowingrate to reduce weed seed-set. The researchshowed that spending $15/ha on increasingphoto: Peter NewmanRyegrass seeds/m 29008007006005004003002001000the sowing rate could halve ryegrass seedset.While this is unlikely to increase cropyield in the short term, with very fewnon-herbicide weed-control tools availableenhancing crop competition against weedscould prove very valuable in the future.Investing in non-herbicide tools, suchas chaff carts and crop competition,enables the paddock to remain in cropby keeping the number of weeds low.Future research may show there isno need to go to extremes of sowingrates, but there is little doubt that thereis significant room for improvementin the area of crop density and controlof herbicide-resistant weeds. □80kg/ha120kg/ha(179 plants/m 2 ) (255 plants/m 2 )Seeding rate/wheat densityGRDC Research Codes DAW00196,DAW00218More information: Peter Newman, AHRI,08 9964 1170, petern@planfarm.com.auFIGURE 1 Impact of wheat sowing density on ryegrassseed production.40kg/ha(138 plants/m 2 )Increasingthe sowingdensity ofwide rowwheat cropsby using astiletto boot(pictured) tocreate pairedcrop rowscan halveryegrassseed-setthroughenhancedcropcompetition.160kg/ha(297 plants/m 2 )SOURCE: DEPARTMENT OF AGRICULTURE AND FOOD, WAManaging herbicide resistance

Cart, crush orcremate weed seeds tomanageresistanceGrowers who successfully control ryegrass in their cropping programsdo so with more than herbicides aloneManaging herbicide resistance8By Dr Michael Walsh and Peter NewmanIf herbicides were the completeanswer to weed control, we would haveeradicated annual ryegrass and wild radishfrom Australian cropping systems long ago.Instead, herbicide-resistant populationsof ryegrass and wild radish are on therise across Australia, with WesternAustralia leading the other states withthe most resistant populations.As herbicides are central to thesuccess of Australian cropping systems,herbicide-resistant weeds represent anenormous threat to farm viability.Despite this grim outlook, the goodnews is that Australia’s growing herbicideresistanceproblem has stimulated aninnovative and integrated approach toweed management, which is now payingdividends in growers’ paddocks acrosssouthern Australia. After adopting the newapproaches many continuous croppers saythey now have fewer weeds than ever before.Exploit the weaknessCentral to the integrated weedmanagement approach has been a betterunderstanding of weed biology andhow to target vulnerable aspects ofthis to drive down weed seedbanks.A major biological weakness of mostsouthern Australian cropping weeds is thattheir seed does not shatter before harvest,providing the potential to remove the weedseed from cropping systems at harvest.Research by the Australian HerbicideResistance Initiative (AHRI) found thatbetween 70 and 98 per cent of weed seedsremained on various weed species at harvest.In the past, these retained weed seedswere harvested and then spread backacross the paddock with the chaff fraction.However, new approaches now focus onremoving the weed seeds from the croppingpaddock. This is achieved by eitherremoving the weed-laden chaff via baling,concentrating the chaff fraction into narrowwindrows for burning, or pulverising thechaff fraction to crush and destroy theweed seeds before they exit the harvester.The benefits of these harvest weedseedcontrol systems is that they removeboth resistant and susceptible weedsthat have survived earlier herbicideapplications, slowing herbicideresistanceevolution and reducing thepressure on subsequent herbicide use.Another weakness of southernAustralian weeds is that their seed doesnot remain viable in the soil for verylong and seedbanks decline rapidly if notreplenished with annual seed production.Consequently, harvest weed-seed controlmethods can lower a very large seedbankof more than 1000 seeds per square metreto 100 seeds/m 2 in only four years.The harvest weed seed control systemshave brought fresh optimism to growerswho have long struggled with herbicideresistantweeds. Many continuous croppersare now able to sow early with theconfidence they have a low weed seedbankburden, and others have not had to usein-crop herbicides in some seasons.Comparing approachesAHRI research compared theeffectiveness of the harvest weedseedcontrol methods – chaff carts,baling, narrow windrow burning andthe Harrington Seed Destructor.Carried out over 25 sites acrossfour states and over two harvests, theresearchers found that each of the harvestweed seed systems was equally as effectiveat removing ryegrass seed from croppingsystems. Averaged across the 25 sites, eachof the weed-seed harvest methods removedabout 55 per cent of annual ryegrass seed.The system chosen will therefore comedown to personal preference and how bestit fits within a particular farming system.Chaff cartsThere has been a significant resurgencein the use of chaff carts in wa, with theaddition of a conveyor belt to deliver thechaff fraction from the harvester to thecart making the system more user-friendly.The conveyor belt adaptation creates chaffdumps that burn out in a shorter period oftime, thus reducing the risk of fire escapes.BalingAn alternative to the in situ burning orgrazing of chaff is to bale all chaff andstraw material as it exits the harvester.Initially developed as a way to improvestraw hay production, the Glenvar BaleDirect System developed by GrahamShields, a grower from Wongan Hills,wa, consists of a large square balerdirectly attached to the harvester, whichcollects and bales all harvest residues.AHRI research shows that 95 percent of annual ryegrass seed entering theharvester was collected in the bales. Inaddition to removing weeds, the balescan be sold or used as a feed source.However, as with all baling systems,the cost of removing nutrients from thecropping system needs to be considered.

Narrow windrow burningA widely adopted alternative to chaff cartshas been to funnel the harvested strawand chaff fraction into narrow windrowsfor subsequent burning in autumn. Thissystem requires only a simple modificationto the harvester and is cheap and easyto use. An estimated 50 per cent of wagrowers have adopted the windrow systemto control herbicide-resistant weeds.According to AHRI and the Departmentof Agriculture and Food, wa (DAFWA),burning narrow windrows consistentlydestroys more weed seed than burningstanding stubble. This is due to the highertemperatureburn achieved in the narrowrows. Concentrating the stubble into anarrow windrow and burning in a light windincreases the intensity of the burn andallows higher temperatures to be reachedfor longer, which is crucial for destroyingweed seeds, especially wild radish.The researchers also calculated thatless than 10 per cent of a paddock isexposed to erosion when burning narrowwindrows rather than the entire paddock.Harrington Seed DestructorDeveloped by wa grower and inventorRay Harrington, the Harrington SeedDestructor (HSD) is a unique weed-seedcontrol system that smashes the chaff andweed-seed fraction as it exits the harvester,destroying seed viability and returning thecrushed fraction to the paddock. Unlikeother weed-seed harvest systems, there isno need for autumn burning and chaff andweed nutrients remain in the paddock.AHRI research has shown that the HSDconsistently destroys 95 per cent of annualryegrass, wild radish, wild oats and bromegrass seed present in the chaff fraction.Total controlCombined with a pre-emergent herbicide,DAFWA research has shown harvestweed-seed systems to be highly effectiveat removing the final few weeds incropping paddocks (Figure 1).The research has monitored the impactof pre-emergent herbicides with and withoutnarrow windrow burning and chaff carts onthe ryegrass populations of 31 northern wacropping paddocks over the past 13 years.Despite starting with a larger seedbank,growers who implemented regular harvestweed-seed control in the form of narrowwindrow burning or chaff carts erodedtheir ryegrass population to very lowlevels in four years. By year eight, thesegrowers had fully depleted ryegrass fromtheir focus paddocks and since then haveaveraged fewer than 1.5 ryegrass plants/m 2 .While the herbicide-only growershave also been very successful at erodingthe ryegrass seedbank, such a heavyFIGURE 1 Combining herbicidecontrol with harvest weed seedcontrol enables full removal ofall ryegrass plants.Ryegrass (plants/m 2 )504030201002001200220032004200520062007200820092010YearHerbicides onlyPlus harvest weed-seed control20112012SOURCE: DEPARTMENT OF AGRICULTURE AND FOOD, WAreliance on herbicides is likely to resultin higher levels of herbicide resistancein these paddocks, making the fewremaining plants expensive to contain. □GRDC Research Codes DAW00196,UWA00124More information: Michael Walsh,08 6488 7872, michael.walsh@uwa.edu.au;Peter Newman, 08 9964 1170,petern@planfarm.com.au9Managing herbicide resistanceNarrow windrow burningachieves a higher-temperatureburn and consistently killsmore weed seeds than burningstanding stubble.photos: Lisa Mayer, Australian Herbicide Resistance InitiativeA conveyer belt adaptation forchaff carts captures a smallamount of straw with the chaff,which significantly increases theburn time of the chaff dump.Up to 95 per cent of annualryegrass seed entering theharvester can be collectedusing a baling system toweddirectly behind the harvester.The Harrington SeedDestructor removes up to 95per cent of weed seed enteringthe harvester, foregoing theneed for an autumn burn.

Glyphosate resistance forcesnew approachGlyphosate-resistant fleabane and barnyard grass arenow widespread in the northern cropping regionManaging herbicide resistance10By Associate Professor SteveWalker and Dr Michael WidderickFive of Australia’s six glyphosateresistantweed species can be foundin the northern growing region whereseveral decades of glyphosate use tocontrol fallow weeds have selectedfor herbicide-resistant populations.Weed-free fallows are essential forconserving soil moisture and maximisingyields of the region’s winter and summercrops but an over-reliance on glyphosate(some growers are using six applicationsover the fallow) is threatening the viabilityof the area’s no-till cropping systems.Topping the region’s herbicide-resistancelist is Australia’s first glyphosate-resistantbroadleaf weed, flaxleaf fleabane, whichin some cases has proved resistant to eighttimes the normal rate of glyphosate.Barnyard grass is a close secondon the list, with half of the testedpopulations identified as resistant.GRDC-funded research by theQueensland Department of Agriculture,Fisheries and Forestry, the University ofQueensland and the New South WalesDepartment of Primary Industries hasidentified chemical and non-chemicaltactics to control glyphosate-resistantweeds and extend the life of thevaluable knockdown herbicide.Fortunately, many of the weedsthat dominate northern region no-tillcropping systems produce seeds thatare short-lived in the soil. This meansthat with just a few years of preventingseed-set the weed seedbank can bereduced by up to 99 per cent.FleabaneAn inability to germinate from deeper thanone centimetre makes fleabane particularlysusceptible to cultivation. Strategic tillageto bury weed seed ‘blow-outs’ has proved asuccessful control tool for this troublesomeweed, which is capable of producingtwo or three flushes of new seedlingseach year and 110,000 seeds per plant.A strategic tillage event usingharrows, tynes, offset discs or onewaydiscs reduced subsequent fleabaneemergence by about 90 per cent of thatin zero-tilled plots in recent researchat Tamworth, NSW (Figure 1).The results show that even aharrow operation, which results in arelatively shallow soil disturbance,has a large and significant impact onfleabane emergence. However, themore disruptive one-way discs decreaseseedling emergence to near zero.A one-off tillage operation to copewith a severe fleabane blow-out wouldbe enough to set back the weed seedbankto a manageable level, which couldthen be further reduced using herbicidecontrol such as the double-knock tactic.Fleabane double knockA correctly used double-knock approachwith applications of herbicides from twodifferent mode-of-action groups, such as aglyphosate mixture followed by paraquatand diquat five to 10 days later, can resultin complete fleabane control (Table 1).It is important to remember thateven susceptible fleabane populationsare difficult to control with glyphosate,especially once the weed has grownpast the seedling stage. Fleabane controlusing the double-knock can declinesubstantially on older rosettes (twomonths old) compared with youngerrosettes (one month old) (Figure 2).The paraquat and diquat applicationis used to ‘finish off’ any survivors. Theaim is to achieve a large (more than 80per cent) control rate using the first knock(glyphosate mix) and to kill the remaining20 per cent or so of survivors with thesecond knock (paraquat and diquat).Including a residual herbicide in thesecond knock can provide excellent longtermcontrol of fleabane in fallows.It is critical to monitor paddocks postsprayingand clean up any survivors.CONTROLLING barnyardGRASS AND FLEABANE• Monitor paddocks for new flushesespecially in autumn and spring forfleabane and spring and summer forbarnyard grass.• In fallows, spray small weeds (lessthan five centimetres in diameter) forfleabane and seedling to early tillering forbarnyard grass. Remember: knockdownefficacy drops markedly on older andlarger weeds.• To minimise replenishment of theseedbank, use the double-knock tacticby spraying paraquat products aboutseven days after the first knock.• Consider adding a residual to thedouble-knock for season-long control.• Follow-up sprayed survivors with robustrates of knockdowns using a weeddetector sprayer as outlined in the newWeedSeeker ® permit (PER11163).• Grow a competitive crop and usein-crop spraying to control small weeds.Fleabane can be more reliably and morereadily controlled using a double-knockapproach instead of a single glyphosatemixapplication. In recent research,fleabane control was increased by fiveto 10 per cent and variation in controlreduced by as much as 30 per cent using adouble-knock approach compared with asingle knock of glyphosate mix (Table 1).Barnyard grassFallow control of barnyard control iscritical to controlling the weed’s seedbank.While glyphosate has been the mainstay ofbarnyard control, increasing glyphosateresistantpopulations of the weed hasforced a rethink of its management.In a survey of fallow paddocks betweenDalby, Queensland, and Tamworth, NSW,that had recently been sprayed withglyphosate, nearly 90 per cent of barnyardgrass survivors were identified as glyphosateresistant. The resistant populations

Row A Row B Row C Row Dwere concentrated between Narrabri,NSW, and Goondiwindi, Queensland.With its staggered emergence,highly competitive growth habit andability to produce up to 20,000 seedsper plant, barnyard grass can quicklybecome a significant problem.As with fleabane, effective barnyardcontrol centres on using multiple tacticssuch as a double-knock, residual herbicidesand strategic tillage to bury weed seed atdepth. Monitoring for survivors regardlessof their scarcity and preventing them fromsetting seed is a necessity – especiallyin herbicide-resistant populations.Strategic tillage reduces barnyardemergence, but to a lesser extent thanfleabane because the grass can emergefrom deeper in the soil (two to fourcentimetres) and can also remain viablefor longer at depth. Tillage can bury seedsbelow 5cm but some of those remainingabove this depth will still emerge.Glyphosate applied alone at robust rateson young (early-tillering) plants can lift killrates on glyphosate-susceptible barnyardgrass to 100 per cent (Figure 3). Timingof the glyphosate application is critical,with a delay of just one week reducingweed control dramatically because largeror moisture-stressed plants do not absorbthe glyphosate effectively. The double-photos: Steve WalkerBarnyard double-knock approach. The double-knock approach is now a necessity forcontrolling widespread herbicide-resistant barnyard grass and fleabane populations acrossthe northern growing region. Pictured are glyphosate-resistant (rows A and C) and glyphosatesusceptible(rows B and D) barnyard grass populations that have been sprayed with either a singleglyphosate application (left photo) or a double-knock of glyphosate followed by paraquat and diquat(right photo). Resistant populations are not controlled with glyphosate alone.knock is needed to control survivors oflarger or glyphosate-resistant plants.Adding a residual herbicide to thedouble-knock can provide good controlof the weed in fallows. Several registeredresidual herbicides, such as Flame ® andatrazine, have been shown to have goodcontrol (83 to 96 per cent) of barnyard grassfor a minimum of a month in fallow. □GRDC Research Code UQ00062More information: Associate ProfessorSteven Walker, University of Queensland,s.walker11@uq.edu.au; Dr MichaelWidderick, Queensland DAFF,michael.widderick@daff.qld.gov.au11Managing herbicide resistanceFIGURE 1 Comparison of zerotillageand strategic tillage onfleabane emergence in thenorthern growing region.FIGURE 2 Impact of doubleknock(glyphosate mix followedby Spray.Seed ® ) or a singleapplication of a glyphosate mixon control of small and largefleabane plants in the northerngrowing region.Fleabane emergence (m 2 ) Control (%) Barnyard control (%)250100100+ 2,4-D followed by paraquat + diquat00 0Zero Harrows Tynes Off-set One-way 0 1 2 3 4 Earlytilleddiscs discsWeed age (months)tillering +high rate2001508060 ‘Single knock’ glyphosate +8060Tordon 75-D ® (picloram) + 2,4-D10040 ‘Double knock’ glyphoshate + 2,4-D followedby paraquat + diquat‘Single knock’ glyphosate + 2,4-D amine5020‘Double knock’ glyphosate + Tordon 75-D ® (picloram)4020FIGURE 3 Impact of low andhigh glyphosate rates on controlof small (early tillering) andlarge (late tillering) barnyardgrass plants in the northerngrowing region.Latetillering +low rateGlyphosate susceptible Glyphosate resistantNote: This research is a combined effort between the University of Queensland, the Queensland Department of Agriculture, Fisheries and Forestry and the NSW Department of Primary IndustriesTable 1 Impact of a glyphosate mix (first knock only) or a double-knock of glyphosate mixfollowed by paraquat and diquat on level of fleabane control in the northern growing region.Double-knock (first knock followed seven days laterFirst knock onlyby a second knock of Spray.Seed ® )Herbicide Mean (%) Range (%) Herbicide Mean (%) Range (%)Glyphosate + Tordon 75-D ® 95.7 86–99 Spray.Seed ® 99.5 97–100Glyphosate + 2,4-D amine 89.2 62–99 Spray.Seed ® 98.1 93–100

Mechanical optionsHarvest weed seed tactics have now proven their worth in managingweeds across four Australian statesManaging herbicide resistance12Mechanical weed management tactics can remove up to 95 per cent ofryegrass seed (pictured) that enters the harvester.By Charlotte AvesA Grdc-FUnded trial across6000 kilometres of southern Australiahas demonstrated that harvest weed-seedcontrol tactics can have an impressiveimpact on ryegrass populations.In trials spanning Western Australia,South Australia, Victoria and New SouthWales, harvest weed seed methods reducedryegrass emergence by as much as 90 percent in paddocks with low ryegrass burdens.Paddocks with high ryegrass burdens(more than 2000 seeds per square metre)were less responsive, with a 30 to 40 percent reduction in ryegrass emergence. Thisindicates that harvest weed seed managementwill take longer to lower ryegrass populationsin highly infested paddocks where theresidual seedbank is still being exhausted.Across the 14 trial paddocks scatteredbetween Eyre Peninsula, SA, andCoonamble, NSW, narrow windrowburning and the chaff cart proved aseffective as the Harrington Seed Destructor(HSD) at removing ryegrass seed andcost a similar amount per hectare todestroy ryegrass seed (Table 1).Before harvest, ryegrass plants werecounted at each site, along with thenumber of seeds above harvest height (15centimetres). In the following autumn,researchers returned to the sites to countthe number of emerging ryegrass seedlings– enabling the impact of the HSD, chaffcart and narrow windrow burning on theryegrass populations to be determined.Before harvest, ryegrass numbersranged from 1/m 2 to 15/m 2 , which equatedto 28 to 4000 seeds/m 2 above cuttingheight. The average number of ryegrassseeds across the 14 sites was 1270/m 2 .Ryegrass emergence in the autumn wasreduced by about 55 per cent followingharvest weed seed treatment. □GRDC Research Code UWA00124More information: Charlotte Aves,0409 697 352, caves@unimelb.edu.auFully integrated HSD andharvester on the wayThe Harrington Seed Destructor (HSD) isgetting a major design overhaul and will bedirectly incorporated into class 9 and 10headers – saving growers dollars and time.The new, integrated approach aims to useless power and have higher capacity than thecurrently available commercial version, whichneeds to be towed behind the header.University of Adelaide researchers testedthe GRDC-funded integrated HSD initially ona Case header in January 2013.Instead of the chaff section needing tobe flipped out the top of the harvester andpushed into the mill, the new approachprocesses the chaff at the point where itexits the header, enabling the straw to flowthrough into the spreader.Despite using the header’s power system,the new prototype processes chaff at morethan 30 tonnes per hour, spreading thecrushed mixture consistently across thepaddock. The commercial tow-behind HSDwill still be available as required for class 6, 7and 8 headers.With GRDC funding, University of Adelaideresearchers have begun developing a newversion of the Harrington Seed Destructor byincorporating the tow-behind milling unit into aclass 9 header.Table 1 Impact of the Harrington Seed Destructor, narrowwindrow burning and chaff cart methods on autumn ryegrassdensity in 14 cropping paddocks across southern Australia.Weed seed management toolReduction in ryegrass emergence (%)Low ryegrass burdenHigh ryegrass burdenChaff cart 75 30Windrow burn 90 29Harrington Seed Destructor 86 38LSD (p=0.05) 12 31photo: Nicole Baxterphoto: GRDC

Selective spraying cuts costs15A new permit in place across Australia will help growers tackleherbicide-resistant grasses with weed-detecting technologyBy Tony CookIncreased use of no-till croppingand an increasing incidence of summerrain have stimulated many growers toinclude a predominantly glyphosatefallow over summer to remove weedsand conserve moisture for the next crop.To reduce the risk of glyphosateresistance developing in fallow weedssome growers are using weed-detectingtechnology to detect individual weedsthat have survived the glyphosateapplication and spraying these with analternative knockdown herbicide.The key to successful resistancemanagement is killing the last fewindividuals, but this becomes ratherdifficult on large-scale properties. Leftuncontrolled, these last few weedsresult in significant seed productionand a resetting of the weed seedbank.The introduction of weed-detectingtechnology is timely as it is well suitedto detecting patches of weeds acrosslarge areas. Sales of the two systemsavailable in Australia, WeedSeeker ® andWEEDit ® , have increased by at least 30per cent anually over the past two years.The technology uses optical sensors toturn on spray nozzles only when green weedsare detected, greatly reducing total herbicideuse per hectare. The units have their ownlight source so can be used day or night.Rather than spray a blanket amount ofthe herbicide across a paddock, the weeddetectingtechnology enables the user toapply higher herbicide rates (per plant),which results in more effective weedcontrol and saves on herbicide costs.Special permitWeed-detecting technology (viaWeedSeeker ® ) is being used to manageglyphosate-resistant grasses in northernNSW fallows with the aid of a minoruse permit. This allows growers in theregion to use selective grass herbicidesand higher rates of paraquat and diquat(bipyridyl herbicides, Group L). Thepermit (PER11163) is in force until 28Feburary 2015 to cover all Australianstates and will be reviewed annually.The permit allows the use of about 30different herbicides from groups with sevenmodes of action. Additional modes of actionare likely to be added to the permit over time.Some herbicide rates have beenincreased to enable control of largeror stressed weeds. For example, theglyphosate 450 (450 grams of glyphosateper litre) rates range from three to fourlitres per hectare (using a set waterrate of 100L/ha), which far exceeds thelabel blanket rates of 0.4 to 2.4L/ha.Similar increases in rate have also beenpermitted for paraquat (Gramaxone ® ).The WeedSeeker ® permit system is alifesaver for zero and minimum-tillagesystems battling glyphosate-resistant weedsas it represents a more economical way tocarry out a double knock and avoids theneed to cultivate for weed seed burial.The new technology also has the potentialto map troublesome weed patches so thatthese areas can be targeted with a preemergentherbicide before sowing. □GRDC Research Code UQ00062More information: Tony Cook, 02 6763 1250,tony.cook@industry.nsw.gov.auphoto: Evan CollisManaging herbicide resistanceSimon Tiller, a growerfrom Esperance inWestern Australia,adjusting hisWeedSeeker ® boomspray. It uses infraredsensors to identifyand spray weeds.