Herbicide resistance - Grains Research & Development Corporation

When used in conjuction with othertactics such as a ‘spray graze’, postharvestgrazing can assist weedmanagement and may improve cropestablishment in the following season byreducing stubble loads.a non-chemical measure, such as heavygrazing or cultivation.It most commonly refers to two herbicideapplications from different MOA groups,between two and 10 days apart. This isoften glyphosate (Group M) or glyphosateplus 2,4-D (Group I) followed by paraquator paraquat plus diquat (both Group L).Double knock is an extremely effectivetactic when done properly, but it requiresattention to detail and can be expensive.It has been proven to delay the onset ofherbicide resistance.Target small weedsMost weeds are less responsive tochemical control once they have grownbeyond seedling stage. It is crucial to targetsmall (pre to early tillering/small rosette)actively growing weeds when spraying.Monitor paddocks post-spraying and cleanupany survivors.There are limitations with registration ofsome of the common herbicides. Somelabels state only a particular growth stageand not beyond. Some labels suggesthigher rates for larger weeds. Always readthe product label for recommendations forweed size, adjuvants and rates.Crop competitionCrop competition is driven by crop typeand variety choice, and works by usingcrop uniformity, density, vigour and goodagronomy to outcompete weeds. It worksbest with cereal crops.The weeds that emerge before or with thecrop are the ones that are more competitivethan weeds germinating after the crop isestablished. Before crop competition kicksin aim to control with herbicides to gain ahead start.Late season herbicide useCrop-topping is the application of a nonselectiveherbicide such as glyphosatePhoto: SARAH CLARRY(wheat and pulses) or paraquat (pulses only)prior to harvest when the target weed is atflowering/early grain fill.The selectivity of the crop-topping processis dependent on a sufficient gap in maturitybetween crop and weed and will bedetermined by crop type and seasonalconditions.Selective spray-topping is the techniqueof using selective herbicides to controlseed production of a weed within acrop prior to head emergence and thusreduce future weed populations. Correctlyexecuted, selective spray-topping canresult in a 90 per cent reduction in weedseed-set, provided there is no resistanceto the MOA. It is not a substitute for earlyweed control and occurs too late forsignificant yield protection.See Useful Resources for more informationon late season herbicide use.HayCutting oats and other cereals for hay canreduce ryegrass seedbanks by 80 to 85 percent. It is not as successful in wild oats orbrome grass because of their early maturity.Cut the hay early before ryegrass hasviable seed. If there is moisture present,come back with a knock down herbicide tocontrol any regrowth.Brown manuringBrown manuring is the growing of acrop, pasture or weeds, which are thensprayed out before weeds set seed.Brown manuring has the advantagesof competition and high weed seed-setcontrol, maintaining ground cover, reducingthe number of applications of herbicide,particularly when compared with longfallow, and improving the yield of followingcrops through increased nitrogen availability,storage of soil moisture and reduction incereal root disease.It can be used to patch-treat problemareas and prevent weed seed being spreadby the header, but is better as a plannedoption for a whole paddock.Harvest weed seed controlWeed seed management at harvest will notfix all weed problems that growers face, butit is the most important non-herbicide toolfor grain growers.Harvest weed seed management includesnarrow windrow burning, chaff carts andseed destruction at harvest.All methods rely on weed seeds enteringpage 5the harvester, therefore the closer theharvest is to weed maturity, the greater theproportion of weed seeds that will be collected.Harrington Seed DestructorThe Harrington Seed Destructor (HSD),which is being trialled around the country,processes the chaff material exiting theharvester and has been shown to destroya high percentage of weed seed present inthe chaff fraction. HSD efficacy will declinewith weed seed shedding associated withdelays in harvest.The Harrington Seed Destructor destroysthe weed seed in one pass without theneed to come back and burn and leavesthe residue (containing nutrients) spread inthe paddock. This will make it an attractiveoption for some growers.Weed-detection technologiesWeed-detection technologies such asWeedSeeker ® and WEEDit use opticalinfra-red sensors connected to solenoidswitches that turn boom-mountednozzles on and off when a green weedis detected in a fallow. There is potentialfor huge savings in summer fallow weedmanagement, as only five to 15 per cent ofthe field will normally be sprayed.NSW growers using a WeedSeeker ®now have access to a permit (Per11163).This allows the use of a wider range ofherbicides, and at higher rates, to managelarger, stressed or harder-to-control weeds.This technology has the ability to delay orprevent the onset of glyphosate resistance.For fallow weeds it allows the use ofalternative herbicides to glyphosate athigher rates that may not be economicallyviable for a blanket application.MonitorWith any weed-control measure, alwaysscout for surviving weeds that couldindicate potential resistance and follow-upwith spot spraying and/or management.Thorough paddock monitoring soon afterspraying will ensure that any spray failuresare detected early before a weed seed blowout has occurred. Not detecting a sprayfailure until harvest can have potentiallydevasting economic consequences. Yearsof hard work and expense will be requiredto bring the seed bank back under control.Knowing the status of weed populationsand how well control measures areworking, are the key to ensuring optimalweed management decisions.

Frequently asked questionsHow do I know if I have a problem with resistance?Normally resistance is first noticed as patches of uncontrolled weeds following aherbicide application. Take samples from these patches for testing. See UsefulResources for contact details for testing services.What herbicides should I test?The aim of testing is to find out what still works. Discuss with the test provider whichherbicides you are likely to use in the future.What do I put in for first and second knock in a double knock treatment?Double knock refers to any two different weed control tactics, chemical or non-chemical,practised in close succession, where the second measure controls survivors of the first.Although it most commonly refers to two herbicide applications from different MOAgroups, you need to consider the target weed and any existing resistance issues beforedeciding on which measure to apply for each knock.Most commonly, glyphosate is the primary first herbicide as it controls a broad spectrumof weeds.What timing should I apply between knocks in a double knock treatment?Generally between two and 10 days, although the interval can be anything from one to14 days, depending on the mix of herbicides to be used, conditions and weed species.Will using tank mixes reduce the chance of glyphosate resistance developing? To be effective in reducing the risk of glyphosate resistance, the tank mix partner mustbe fully compatible with glyphosate and must be applied at a rate that will kill anyglyphosate-resistant plants in the treated population. Most tank mix partners are onlyadded to increase the broadleafed weed spectrum targeted and therefore do not reducethe selection pressure for grass weeds developing resistance to glyphosate.Can tillage lower the risk of resistant weeds? Yes, but only if the survivors are killed by the cultivation. For this to happen, thecultivation needs to be well timed and executed.How do I control mature plants?Double knock with higher rates of herbicide, for example spot spraying, may providecontrol, but in some instances cultivation may be the only cost-effective option.more informationJohn Broster, Charles Sturt University02 6933 4001; jbroster@csu.edu.auJohn Cameron, ICAN Rural02 9482 4930; john@icanrural.com.auChris Preston, University of Adelaide08 8313 7237; christopher.preston@adelaide.edu.auAndrew Storrie, Agronomo Consulting08 9842 3598; andrew@agronomo.com.auUseful ResourcesFor testing suspectedresistant samples:Charles Sturt UniversityHerbicide Resistance Testing,School of Agricultural and WineSciencesCharles Sturt UniversityLocked Bag 588Wagga Wagga NSW 267802 6933 4001www.csu.edu.au/research/grahamcentre/producers/herbicideresistancetesting.htmPlant Science Consulting22 Linley AveProspect SA 50820400 664 460info@plantscienceconsulting.com.auwww.plantscienceconsulting.comAustralian Herbicide ResistanceInitiative (AHRI)www.ahri.uwa.edu.auCurrent Herbicide ResistanceStatus (International)www.weedscience.orgGlyphosate ResistanceAustralian Glyphosate SustainabilityWorking Groupwww.glyphosateresistance.org.auGRDC Weedlinkswww.grdc.com.au/weedlinksIntegrated Weed Management inAustralian Cropping Systemswww.glyphosateresistance.org.au/manual.htmlLate Season Herbicide Usewww.grdc.com.au/uploads/documents/GRDC_LateSeasonHerbicideUse_FS1.pdfWeed Seed Wizardwww.agric.wa.gov.au/PC_93813.html?s=1001GRDC Project codeSUA00104, UA00113, UA00121,UWA00124Acknowledgments: Peter Boutsalis, JohnBroster, John Cameron, Gurjeet Gill, ChrisPreston and Andrew Storrie.DisclaimerAny recommendations, suggestions or opinions contained in this publication do not necessarily represent the policy or views of the Grains Research and Development Corporation.No person should act on the basis of the contents of this publication without first obtaining specific, independent professional advice.The Corporation and contributors to this Fact Sheet may identify products by proprietary or trade names to help readers identify particular types of products.We do not endorse or recommend the products of any manufacturer referred to. Other products may perform as well as or better than those specifically referred to.The GRDC will not be liable for any loss, damage, cost or expense incurred or arising by reason of any person using or relying on the information in this publication.CAUTION: RESEARCH ON UNREGISTERED PESTICIDE USEAny research with unregistered pesticides or of unregistered products reported in this document does not constitute a recommendation for that particular use by the authors or theauthors’ organisations.All pesticide applications must accord with the currently registered label for that particular pesticide, crop, pest and region.Copyright © All material published in this Fact Sheet is copyright protected and may not be reproduced in any form without written permission from the GRDC.produced by www.coretext.com.aupage 6