Section 2 Integrated weed management (IWM) - Weeds Australia

More documents

Recommendations

Info

Herbicide resistanceWhat is herbicide resistance?Herbicide resistance is the ability of a plantto survive and reproduce following exposureto a dose of herbicide that would normally belethal. In a plant, resistance may occur naturallydue to selection or it may be induced throughtechniques such as genetic engineering.Resistance occurs in plants as a result of randomand infrequent mutations. Through selection,susceptible plants are killed while herbicideresistant plants survive to reproduce withoutthe competition from susceptible plants. If theherbicide treatment is repeated, resistant plantssuccessfully reproduce and become dominantin the population. The appearance of herbicideresistance in a plant population is an example ofrapid weed evolution.Serrated tussock resistance toflupropanateFlupropanate is a soil active herbicide that hasresidual activity and can prevent serrated tussockfrom regrowing for three to five years (Campbelland Vere 1995). It is classified as a Group Jherbicide that inhibits plant lipid synthesis andis regarded as a moderate risk herbicide forresistance (Croplife Australia 2007).Herbicides that have long soil residual andseason-long control of germinating weeds, likeflupropanate, characteristically increase selectionpressure and the likelihood of resistance (Figure5).There are now three separate confirmedinstances of serrated tussock populationsresistant to flupropanate in NSW and Victoria.The continued use of flupropanate over a 15–20year period is the most likely cause of theseresistant strains developing (McLaren et al.2008).Flupropanate – one application provides soil residualcontrol of germinating serrated tussock for 3–5 years.Serrated tussock reproduction andimplications for serrated tussockresistanceSerrated tussock reproduces by producing seedthat can travel long distance (see page 10).Research has shown that 85−90% of serratedtussock flowers don’t open at flowering. Insteadthey exchange pollen within the unopened flowerand produce a clone of the parent plant. Thismeans that a resistant plant will produce at least85−90% resistant seed.Research has also shown that pollen from aresistant serrated tussock plant can createresistant seeds in a wild type susceptibleserrated tussock plant, but at very low ratios(1:29). The good news is that only 10−15% ofserrated tussock seeds are open for pollination,resulting in smaller opportunities for crossfertilisation and production of resistant seeds.However, the prolific seeding capacities ofserrated tussock does make this possible andpollen induced resistance has been recorded inVictoria.How far can a serrated tussock pollen graintravel? At this stage it is not known; however,genetically marked pollen from the perennialgrass, brown top bent grass, has been recordedfertilising wild plants 21 km from its source.The long term implications of serrated tussockherbicide resistance are:• its increased dominance as a weed• increased costs for land managers• more herbicide usage• higher environmental pollution as aconsequence.It is now appropriate to undertake serratedtussock flupropanate resistance paddock surveysaround the properties identified, to determinethe extent of resistance and take appropriateremedial actions.There is also growing global concern regardingresistance to glyphosate. Luckily at this stagethere have been no reported instances ofglyphosate resistance in serrated tussock.Reduce the risk of herbicide resistanceby rotating chemicals with differentmodes of actions and use IWM.Figure 5: Herbicides that have long soil residualand season-long control of germinating weedscharacteristically increase selection pressure andthe likelihood of resistance.24
Ways to avoid herbicide resistance1. Most importantly—do not rely solely on theuse of chemicals for control.2. Use immediate acting or short residualherbicides whenever possible. Use longterm residual herbicides (like flupropanate)wisely and not continuously on the samefield.3. Integrate herbicide use with other weedcontrol strategies (practice IWM).4. Always apply herbicides according to labeldirections.5. Regularly rotate the herbicide typesused with different modes of action. Forexample, Group J (flupropanate) or Group M(glyphosate).6. Always monitor and follow up control onany re-growing serrated tussock plants.7. Check sprayed areas for resistant plants.If there are any plants that have not beenaffected by the herbicide application, alwaysinvestigate the reason why it happened.8. Practice good sanitation practices to reducemovement of weed seed.9. Do not let any serrated tussock plant setseed.Managing flupropanateresistanceIn 2007 a property near Armidale in the NewEngland Tablelands of NSW was identifiedas having a population of serrated tussockresistant to the herbicide, flupropanate. Priorto this, the property had relied heavily onbroadacre spray applications of flupropanatein their serrated tussock control program.The resistant serrated tussock currentlycovers about 20 ha of land and is the target ofa control program. The affected area has beencultivated and a cover crop of oats has beensown with pasture underneath.Spraying with flupropanate has beendisbanded and spot spraying program usingglyphosate is being used instead. Stricthygiene protocols are being employed toprevent serrated tussock seed leaving theproperty from stock, vehicles or machinery.While this option is time consuming and maycause some pasture damage, there is little elsethey can do. There is no short-term solutionand ongoing resources are required to controlthe population of resistant serrated tussock.James BrowningAt this stage it is too early to tell howsuccessful the cropping phase will be;however, previous pasture renovation theyhave undertaken on the property has workedwell with the property now at a spot sprayprogramme that is progressively reducinglevel.Population of serrated tussock resistant to flupropanate.Area where flupropanate resistant tussock has beencultivated and sown to oats.James BrowningThe same property after cropping and pasturerenovations.25
Page 3: Serrated tussock and integratedweed
Page 7: The need for broadercommunity and/o
Page 10 and 11: Keeping a photographic recordTaking
Page 12 and 13: Step 2: Set your objectivesObjectiv
Page 14 and 15: Step 4: Monitor outcomes and adjust
Page 16 and 17: A community basedapproach to managi
Page 18: Field day focussed on serrated tuss

Section 2 Integrated weed management (IWM) - Weeds Australia

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?