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Field Lab Weed Science Research

Weed Science Research

Current Research Projects

Our research projects are centred around agricultural weeds of concern to growers and are constantly adapting and evolving according to our latest findings.
A selection of our projects are described below. Under each project title you will find some background information, project aims, weed species in focus and the key researchers involved. Projects conducted by our PhD and Honours students are also featured.

  • Mechanisms, evolution and inheritance of resistance

    Herbicide resistance in weeds limits the options available to growers to control weeds in an efficient and cost-effective manner, making them a major threat to profitable grain production systems in Australia. Herbicide resistant weed populations have been discovered throughout Australia including in grain crops, fallows, orchards, vineyards, fencelines and irrigation channels. This project is concentrating on key existing and emerging weed resistance issues of importance to Australian grain growers.

    This study is designed to investigate

    • The biochemical and molecular mechanisms involved in resistance, such as target-site mutations, reduced translocation of herbicides throughout the plant, gene amplification and rapid necrosis. 
    • How selection for herbicide resistance mechanisms occur in the various weed species and populations. 
    • The evolutionary dynamics of herbicide resistance e.g. inheritance studies to determine the number and cross-resistance patterns of genes contributing to resistance.
    • The most effective approach to manage various herbicide resistance situations.

    Weed species and herbicide resistances in focus

    • Glyphosate resistance in brome grass, barnyard grass, sowthistle and feathertop Rhodes grass 
    • Diflufenican and 2,4-D resistance in Indian hedge mustard 
    • Phenoxy herbicide resistance in sowthistle
    • Clethodim resistance in ryegrass
    • Resistance to pre-emergent herbicides in annual ryegrass

    The knowledge gained from this project will underpin strategies to delay the onset of herbicide resistance and also to manage the impact of existing resistances, by informing appropriate rotations and sequences of herbicide applications as part of an integrated weed management strategy. Better herbicide choices by growers will delay the onset of resistance to key herbicides in their crop rotations.

    Researchers

    Key Collaborators

    This project is led by the University of Adelaide and our researchers have established collaborations with several American-based researchers and their teams, including:

  • Crop competition for weed management and maintenance of crop yield

    Dr Gurjeet Gill is leading a new GRDC funded project to investigate the integration of cultural weed control tactics with herbicides to improve crop competitiveness against weeds across different rainfall zones in the southern and western grain growing regions. Research in Western Australia will be led by Dr Mike Ashworth.

    This project will allow researchers to determine the stability of the performance of different weed control tactics against ryegrass, brome grass and wild radish across the different rainfall zones and regions. The project will be undertaken collaboratively with farming systems groups in the southern and western regions, enabling rapid transfer of project outputs to growers and advisers.

    This study is designed to

    • Quantify the effect of combinations of crop competition factors on weed seed-set and crop yield;
    • Refine strategies and improve crop competitiveness across different rainfall environments
      in the southern and western regions of Australia.

    Crop species in focus

    • Southern region: Wheat, Barley, Canola and Faba Bean
    • Western region: Wheat, Canola and Narrow Leaf Lupins

    Weed species in focus

    • Ryegrass
    • Brome grass
    • Wild radish

    Researchers

    Key Collaborators

    This project is led by the University of Adelaide and involves several groups including:

  • Management of annual ryegrass in the high rainfall zone

    Annual ryegrass can be particularly challenging to manage in the high rainfall zone (HRZ). Widespread resistance to post-emergent herbicides used in cereals means there is strong reliance on pre-emergent herbicides for ryegrass control. Annual ryegrass seed banks in the HRZ tend to be high and there is late emergence of weeds due to the long and cool growing season. These late emerging plants contribute to high seed set that maintains populations. As a result, ryegrass populations quickly rebound when management pressure is reduced. Late maturity of cereals means that 50% or more of the ryegrass seed can be shed prior to harvest, reducing the efficacy of harvest weed seed controls. On the plus side, moderate populations of ryegrass (<100 plants per m2) have less impact on yield than they do in other regions.

    This project aims to demonstrate annual ryegrass management strategies in the HRZ, providing confidence for agronomists and growers to make on-farm management changes that are effective and profitable.

    The Project:

    • Five demonstration sites have been established across southern Victoria and the SE of South Australia. 
    • Sites are sown to break crops in 2018 and will have wheat in 2019.
    • Each site has 4 annual ryegrass management strategies with increasing management intensity to demonstrate strategies that may provide effective and profitable management of annual ryegrass in the HRZ.
    • The management strategies employed at each site have been developed with local agronomists.
    • There will be opportunities to view the sites during the season.

    Plot plans, treatments and data collected at each site is available via the HRZ ryegrass management portal.

    Researchers

    Key Collaborators

  • Emerging weeds: Seed-bank biology of emerging weeds in Australian agricultural systems

    Weed populations are dynamic in nature and changes in farming systems, farm management practices and climate are resulting in a changing weed spectrum. Several weed species that previously were mainly weeds of pastures (e.g. barley grass) have now become significant weeds of crops, thereby increasing costs and reducing yields. Growers are seeking information about the behaviour of these emerging weeds, especially seed-bank persistence, in order to manage them effectively. At present such information on weed seed biology is not available for many of these weed species.

    This study is designed to

    • Review existing knowledge of seed dormancy, life-cycles and seed-bank persistence of identified emerging weed species.
    • Characterise 10 major emerging weed species in each of the northern, southern and western cropping regions of Australia, through field experiments and laboratory studies. To better understand weed seed biology our focus is on the following characteristics:
      • seed dormancy - especially the effect of climate and management practices on seed dormancy
      • seed-bank persistence - build-up and depletion rates, effect of rainfall and depth of seed burial 
      • rate of seed drop (dispersal after maturity) and weed spread 
      • competitiveness with crops 
    • Facilitate development of integrated weed management strategies by providing information on weed seed biology to decision support systems, growers, agronomists and consultants.

    Weed species in focus

    • Grasses
      • brome
      • barley
      • windmill
      • liverseed
      • button
      • sweet summer
      • feathertop Rhodes
    • Other
      • wireweed
      • sowthistle
      • wild turnip
      • bifora
      • roly-poly
      • caltrop
      • turnip weed
      • bladder ketmia
      • prickly lettuce
      • Afghan melon
      • marshmallow
      • Mexican poppy
      • Indian hedge mustard
      • bedstraw/cleavers
      • doublegree/three corner Jack
      • statice/sea lavender

    The knowledge about weed seed and seed-bank biology gained from this project will allow the development of effective control tactics, including integrated weed management strategies, for these emerging weeds. More information about the weed species that are emerging under current management systems will allow growers to make informed decision about their weed management programs in the future, enabling them to reduce the impact and costs of their weed problems.

    Researchers

    Key Collaborators

    This project is led by the University of Adelaide and collaborates with a range of institutions including:

  • Weed management in Australia’s southern region mixed farming systems:
    Strategies to combat herbicide resistance

    Weed infestations result in significant costs to both continuous cropping and mixed farming producers across southern Australia, both in terms of crop productivity and also livestock health and productivity. Changes in weed species spectra and their biology is reducing the efficacy of previously successful weed management strategies. As weeds adapt to changing farming practices evolution of herbicide resistances and weed species shifts occurs, both of which are threatening the continued success of conservation farming systems across the southern region.

    This project aims to develop effective non-chemical and chemical management tactics for strategic use against particular weeds, as well as explore the implementation of cost-effective weed management in mixed cropping systems with pasture rotations. These endeavours will prove critical in limiting the spread of new and emerging weed species and slowing the development of herbicide resistance(s).

    This study is designed to

    • Assess and address the impacts of major weeds in continuous cropping and mixed farming systems across southern Australia. 
    • Evaluate management practices that will be appropriate for controlling weed species in a changing environment where herbicide resistance is problematic.
    • Develop effective management strategies to combat herbicide resistance while maintaining the benefits of conservation farming.

    Led by Prof Leslie Weston from Charles Sturt University, our group is primarily involved with broadacre cropping systems across SA and VIC, and will concentrate on:

    • Surveys of herbicide resistance in key weed species.
    • Research trials for weed epidemiology with a focus on strategic management of 3 key weed issues:
      • Annual ryegrass management in high rainfall zones 
      • Management of clethodim resistant weeds in rotations with high frequencies of break crops
      • Management of imidazolinone resistant brome grass in cereal rotations
    • Identifying new solutions for major weeds in continuous cropping no-till systems, towards development of new knowledge on chemical management strategies and use patterns.

    Weed species in focus

    • Grasses: annual ryegrass, barely, brome, wild oats.
    • Broadleaf: Indian hedge mustard, sowthistle, wild radish.
    • Other weeds found to be present at high frequencies.

    Knowledge gained from this project will result in the development and demonstration of new and effective chemical and cultural management strategies for major weeds in the southern grains and mixed farming region. Findings will assist growers to optimise their weed control tactics in the context of continued profitable no-till farming practice and to also consider the potential of integrating a profitable livestock enterprise.

    Researchers

    Key Collaborators

  • Understanding herbicide resistance to 2,4-D in common sowthistle:
    Improving activity on resistant populations.

    This project is primarily driven by Dr. Mahima Krishnan but whilst she is on extended leave, Dr. Tijana Petrovic has taken on the research challenges.

    Researchers

    Key Collaborator

    • Agricultural Chemical Company
  • New uses for existing chemistry

    Herbicide resistance is a major problem in Australian grain cropping, reducing the herbicide choices available to growers and increasing their costs. There is a need to increase the availability and flexibility of controls for herbicide-resistant weeds, including new herbicide uses. Worldwide, Australia is a small market for agrichemicals and new herbicides typically remain unregistered despite gaining registration in other countries.

    This study is designed to

    • Develop data to facilitate and promote registration of new uses for existing herbicides
    • Identify new uses for existing registered pre- and post-emergent herbicides
    • Register these new uses on herbicide labels or permits
    • Broaden the choice of herbicide uses available to growers

    This project is led by Dr Bhagirath Chauhan from the University of Queensland and our group will primarily concentrate on pot experiments and field trials targeting identification of herbicides that are able to control brome and barley grasses.

    Weed species in focus

    • barley grass
    • brome grass
    • awnless barnyard grass
    • feathertop Rhodes grass
    • fleabane
    • sowthistle
    • wild radish

    Knowledge from this project will make available new herbicide treatments for site-specific management of crop weeds. It will provide growers with more options when tackling problem weeds including those with herbicide resistances.

    Researchers

    Key Collaborators

  • Evolution and management of Group J and K resistance in annual ryegrass (Lolium rigidum)
    David BruntonPhD Candidate: David Brunton

    Supervisors: A/Prof Chris Preston, A/Prof Gurjeet Gill and Dr. Peter Boutsalis

    Annual ryegrass (Lolium rigidum) is a major, cross-pollinated, annual grass weed that occurs in cropping systems of southern Australia. It has been selected through repeat herbicide application and has evolved resistance to a number of major herbicide modes-of-action, including widespread resistance to Group A, B, D and M herbicides. The result has been increased reliance on herbicides from Groups J and K to control ryegrass. Recently resistance to the Group J herbicides triallate (Avadex Xtra®) and prosulfocarb (Arcade and Boxer Gold®) has occurred. Investigating Group J herbicide resistance would provide valuable information to the agricultural community.

    The study objectives are to:

    • Undertake a series of dose-response experiments using multiple group J and K herbicides, to quantify
      and characterise (including LD50 values) resistant annual ryegrass populations
    • Determine the level of cross-resistance to group J and K herbicides;
    • Identify the mechanism(s) that confer resistance to Group J herbicides;
    • Determine the mode of inheritance in ryegrass populations resistant to group J and K herbicides;
    • Identify alternative herbicide strategies in cereal rotations to effectively manage group J and K resistant ryegrass.
    Susceptible and resistant ryegrass

    Different responses of 2 ryegrass biotypes to pre-emergent herbicide treatment.
    Top to bottom: Untreated, Avadex Xtra®, Arcade®, Boxer Gold® and Sakura®.

    Ryegrass escapes after
    pre-emergent herbicide application.

  • Herbicide-resistant common sowthistle and prickly lettuce:
    Dispersal, seed biology and management considerations in lentils.
    Alicia MerriamPhD Candidate: Alicia Merriam

    Supervisors: A/Prof Chris Preston, A/Prof Gurjeet Gill and Dr. Jenna Malone

    Prickly lettuce (Lactuca serriola or wild lettuce) and common sowthistle (Sonchus oleraceus or milkthistle) are two common weeds in the southern cropping region of Australia, and both are problematic particularly in weakly competitive crops such as lentils. They compete for space, water and nutrients both within and outside of the growing season as well as causing problems at harvest. Both species have evolved resistance to herbicides from Groups B, I and M. Due to the wind-borne nature of their seeds, these species can move across the landscape and this is a commonly cited example of why they can be difficult to control. As a result, management tends to be reactive rather than a more proactive Integrated Weed Management (IWM) approach. However, the extent to which seeds move and the role this movement plays in the spread of herbicide resistance is not known. This project will aim to understand gene flow in these species and its implications for management, as well as examine how they might be evolving in response to intensive lentil production.

    Sowthistle flower head

    Sowthistle flower head with mature seed ready for dispersal.

    The main objectives of this project are to:

    • Determine the extent of herbicide resistance in common sowthistle and prickly lettuce in the southern cropping region, particularly in lentil production areas.
    • Determine how much seed moves and how far it travels from parental plants.
    • Establish how effective management during the cereal phase is in controlling weed numbers in the following lentil crop.
    • Determine if and how seedbank biology of these species has evolved in response to intensive lentil production. Are weed seedlings emerging later in the year to escape knockdown and pre-emergent herbicides, and how much of the seedbank is carrying over to subsequent years?

    This project will increase knowledge about the extent and evolution of herbicide resistance, field ecology and seedbank biology, of common sowthistle and prickly lettuce. These insights will improve management strategies for these problematic broadleaf weeds, which will help lentils remain a profitable crop by maintaining sustainability of production.

    Sowthistle and prickly lettuce in a chickpea crop

    These prickly lettuce and sowthistle plants survived herbicide treatments and are able to grow on to produce viable seed.

    Sowthistle and prickly lettuce in a chickpea crop

    Prickly lettuce & sowthistle tower above pulse crops, which facilitates seed dispersal.

    Sowthistle in lentils

    Sowthistle flowering within a lentil crop. 

  • Characterisation and management of glyphosate resistant barley grass (Hordeum glaucum Steud.).
    Patricia Adu-YeboahPhD Candidate: Patricia Adu-Yeboah

    Supervisors: A/Prof Gurjeet Gill, A/Prof Chris Preston and Dr. Jenna Malone

    Barley grass (Hordeum glaucum Steud.) is an annual grass weed which rapidly germinates in autumn and is problematic in both cropping and non-cropping situations in Australia. Whilst it has been confirmed that barley grass populations have evolved resistance to Group B and several Group A herbicides, recently there have been reports of some populations surviving Group M (glyphosate) applications in South Australia. These resistant populations are growing in vineyards, cereal cropping paddocks and along road-sides. My research aims to investigate the resistance of barley grass to glyphosate and develop alternative management strategies.

    barley grass in crop.

    The study objectives are to:

    • Determine the extent of spread of glyphosate resistant barley grass in South Australia, through a physical survey;
    • Assess seed bank characteristics of resistant barley grass populations;
    • Screen barley grass populations from different situations and determine their levels of resistance to glyphosate;
    • Determine the mechanisms of glyphosate resistance;
    • Determine potential fitness penalties associated with glyphosate resistance;
    • Develop effective control strategies for glyphosate resistant barley grass.


    Knowledge gained from this project will assist with the development of effective integrated weed management strategies to slow the rate of glyphosate resistance evolution and to successfully manage already resistant barley grass populations.

    Barley grass in field.

    Barley grass: Is it glyphosate resistant?

    Barley grass RvsS Glyphosate

    Barley grass populations that are susceptible (far left) and resistant to glyphosate.

  • Herbicide resistance of Sisymbrium irio (London rocket).
    Mina TeimouriVisiting PhD Candidate: Mina Teimouri

    Supervisors: A/Prof Chris Preston, A/Prof Gurjeet Gill and Dr. Jenna Malone

    London rocket (S. irio) is an annual or winter-annual tap-rooted plant with yellow flowers. It has been estimated that a large plant can produce 9500 seeds or more (Guertin, 2003). In Australia, the seed germinates from autumn to winter and the plant grows without forming a rosette, branching freely from the base to form a bushy appearance. It's common name ‘London rocket’ arose when it became abundant after the Great Fire of London in 1666.

    Resistance to herbicides from mode-of-action Group F is suspected to have developed in London rocket, in southern Australia. Mina's research aims to reveal the extent and nature of this herbicide resistance. Group F herbicides are PDS inhibitors; bleaching chemicals from the Pyridazinones and Pyridinecarboxamides families (actives: norflurazon, diflufenican and picolinafen), which inhibit carotenoid biosynthesis at the phytoene desaturase step (PDS).

    The study objectives are to:

    • Establish the level and type(s) of herbicide resistance in London rocket from southern Australia;
    • Investigate the potential mechanism of confirmed herbicide resistance(s);

    Knowledge gained from this project will assist with developing effective management strategies for London rocket.

    References:
    CABI, 2018. Sisymbrium irio. In: Invasive Species Compendium. Wallingford, UK: CAB International. CABI Datasheet.
    Guertin P, 2003. Factsheet for Sisymbrium irio L.  U.S. Geological Survey / Southwest Biological Science Center, 24 pp.

  • Effect of ecological and genetic factors on seed germination of annual ryegrass (Lolium rigidum) and brome grass (Bromus diandrus).
    Zarka RamizPhD Candidate: Zarka Ramiz

    Supervisors: A/Prof Gurjeet Gill, A/Prof Chris Preston and Dr. Jenna Malone.

    Historically, herbicides are an efficient way of controlling crop weeds but their continual use is selecting for weeds survivors, which then dominate the population and become problematic for growers. Surviving weeds may be able to enzymatically detoxify the herbicide, or they may contain an altered herbicide target site that prevents the herbicide from binding, or perhaps another mechanism of resistance is present. Greater weed seed dormancy is also being selected for by long-term use of herbicides, because these weeds physically avoid the herbicide treatment. For this situation, studies on seed germination ecology are valuable.

    Weed ecology and germination patterns of problematic weeds have been studied previously. However, none have asked why there is so much variation in germination percentages and emergence patterns, between different populations of the same species, nor how these are controlled at the genetic level. The question of if there are genes responsible for causing germination variation among these populations is yet to be answered. This research will focus on brome grass and ryegrass seed behaviour under conditions of ecological stress, their germination percentages, genetic factors influencing dormancy and differing between early and late germinating weed seeds, and how best to control them.

    The main objectives are to:

    • Investigate germination percentages and emergence patterns over time for germinating ryegrass and brome grass populations, within different rainfall zones;
    • Determine the biochemical basis of dormancy in populations with delayed emergence;
    • Identify genes involved in dormancy for brome grass and ryegrass;
    • Deduce strategies for more effective control of brome grass and ryegrass when using pre-emergent herbicides.

    Knowledge gained from this project will assist with the development of effective integrated weed management (IWM) strategies to slow the rate of resistance evolution and to successfully manage already resistant ryegrass and brome grass populations.

    Brome grass

    Brome grass architecture.

    Flowering ryegrass

    Flowering ryegrass.

  • Herbicide resistance in winter grass (Poa annua) and its management.
    Rajesh BaruaPhD Candidate: Rajesh Barua

    Supervisors: A/Prof Chris Preston, A/Prof Gurjeet Gill and Dr. Peter Boutsalis

    Poa annua Poa annua, also commonly known as annual meadow grass, winter grass or bluegrass, belongs to the family Poaceae and is a common weed wherever cool-season turf-grasses are grown. It is a problematic weed of turf worldwide due to its unsightly appearance, competition with desirable species, and its upright growth habit producing an uneven surface that affects ball roll in golf and other sports. It is also present as a weed in 38 crops such as vegetables, cereals, sugar beet, potatoes, and orchards in 80 countries. This species is usually controlled by herbicides in turf. However, in the recent years, herbicide resistance has been identified in P. annua. In Australia, resistance to 5 herbicide modes of action has been identified in populations of P. annua collected from golf courses including: ALS inhibitors, Photosystem II inhibitors, tubulin biosynthesis inhibitors, glyphosate and endothall. Although there are several previous studies on herbicide resistance in P. annua, there is limited information available on the mechanisms of resistance to herbicides in this species. The aim of this study is to identify the extent of resistance and the mechanisms of resistance associated with herbicide resistance in P. annua and also develop alternate management strategy.

    The main objectives of this project are to:

    • Screen P. annua populations for resistance to different herbicide groups
    • Undertake detailed dose-response experiments to assess the level of resistance (LD50 and GR50)
      in different P. annua populations
    • Explore the herbicide resistance mechanism including the mutations that confer resistance by sequencing target enzymes as well as non-target site mechanisms where needed
    • Identify the mode of inheritance of herbicide resistance of different herbicide groups by segregation of crosses
    • Determine the fitness penalty for resistance to different herbicide groups in F2 populations developed from crosses between R and S populations
    • Identify alternate herbicides to control the resistant P. annua populations

    This project will provide comprehensive information on the nature of resistance to the different herbicides in
    P. annua and the extent of resistance in turf across Australia. This will help determine management options
    by suggesting possible approaches to management, including non-chemical approaches where appropriate.
    Resistance is now suspected in P. annua to propyzamide, which has become an extremely important
    herbicide for the control of multiple herbicide resistant Loilum rigidum populations. Lessons learned from research on propyzamide resistant P. annua could be highly useful for the management of herbicide
    resistant L. rigidum in the future.

    P. annua Pre-em Propyzamide

    Pre-emergent treatment of P. annua with propyzamide confirms resistant populations.

    P. annua Post-em Propyzamide Treatment

    Post-emergent propyzamide treatment
    of P. annua populations. L to R: untreated,
    1/4 x field rate, 1/2 x, 1 x, 2 x, 4 x

  • Herbicide resistance in common sowthistle (Sonchus oleraceus)
    populations from the Yorke Peninsula.
    Honours Student: Daniel Petersen
    Daniel Petersen

    Supervisors: A/Prof Gurjeet Gill and Dr Jenna Malone

    Sonchus oleraceus (common sowthistle) is a self-pollinating dicotyledonous winter annual species that is widespread and common in the southern grains region of Australia. Controlling sowthistle in lentils (Lens culinaris) presents a major challenge for growers because effective control measures are limited. Lentils have poor early vigour, limited vegetative growth and short plant stature, which reduces the competitiveness of the crop for photosynthetically active radiation, water, nutrients and space.

    Minimising seedbank replenishment is difficult, as S. oleraceus seed is wind dispersed and thousands of seeds can be produced from a single plant. Another complexity is that S. oleraceus expresses little innate dormancy, which allows for multiple germinations to occur throughout a growing season in the presence of suitable conditions.

    The extensive use of Group B herbicides (inhibitors of acetolactate synthase) has resulted in the evolution of herbicide resistance in S. oleraceus in southern Australia. Group I (disruptors of plant cell growth) resistance has also been confirmed in S. oleraceus in southern Australia, while Group M resistance (inhibitors of EPSP synthase; glyphosate) has been reported in the northern grains region of Australia. 

    The objectives of this project are to:

    • Determine the extent of Group B, I and M herbicide resistance in S. oleraceus
      in the intensive lentil producing regions of southern Australia;
    • Ascertain the level of resistance to Group B, I and M herbicides in S. oleraceus populations;
    • Identify the mutations that confer Group B resistance in S. oleraceus populations;
    • Establish the effectiveness of pre-harvest desiccation treatments in reducing the
      replenishment of S. oleraceus seedbank;
    • Evaluate the potential for improving harvest weed seed capture of S. oleraceus.

    Determining the extent and mechanism of resistance to Group B, I and M herbicides in intensive lentil producing regions will facilitate effective management of S. oleraceus.

    Common sowthistle in Lentils

    Common sowthistle in a lentil crop prior to desiccation, near Maitland on the Yorke Peninsula, SA.

  • Investigation of herbicide resistance in Sisymbrium orientale (Indian hedge mustard)
    Hue Thi DangPhD Recipient: Hue Thi Dang

    Supervisors: A/Prof Gurjeet Gill, A/Prof Chris Preston and Dr. Jenna Malone

    Indian hedge mustard (IHM) is a serious broadleaf weed in agricultural production systems in southern Australia. IHM resistant to Group B mode-of-action herbicides is well documented in winter crops across Australia, but more recently resistance to other groups, including triazines (Group C), diflufenican (Group F) and phenoxys (Group I), has been identified. There is currently little information available about key aspects of these herbicide resistances, which increases the challenge to control this troublesome weed species. This research aims to reveal the extent and nature of herbicide resistance in Indian hedge mustard.

    Cross-pollination IHM

    Hue delicately cross-pollinates Indian hedge mustard.

    The study objectives are to:

    • Screen IHM populations for resistance to various herbicide groups and subsequently quantify the degree of any resistance displayed;
    • Determine the biochemical/molecular mechanism(s) that confer resistance to different herbicide groups;
    • Quantify potential fitness penalties associated with the particular resistance mechanism evolved;
    • Establish the mode of inheritance for herbicide resistances identified.

    Knowledge gained from this project will assist with the development of effective integrated weed management strategies to slow the rate of resistance evolution and to successfully manage already resistant IHM populations.

    Atrazine RvS IHM

    Comparing atrazine resistant and susceptible Indian hedge mustard (Sisymbrium orientale) populations.

  • Glyphosate  resistant Conyza bonariensis (flaxleaf fleabane) in north east Victoria
    Charlotte AvesPhD Recipient: Charlotte Aves

    Supervisors: Christopher Preston, Gurjeet Gill and Leslie Weston (Charles Sturt University)

    Flaxleaf fleabane is a global weed occurring in over 40 crop types across 70 countries and it is present in every Australian state. It has gained notoriety in the northern grains region as being a weed that is difficult to control and in the Goondiwindi region (Qld) fleabane has increased fallow weed control costs by 100%.

    Flaxleaf fleabane is a species prone to developing herbicide resistance. Glyphosate resistant populations have been reported in 10 countries including Australia, where it is present in Queensland, New South Wales and South Australia. Recently it has become a problem weed throughout the cropping belt of south-eastern Australia.

    The objectives of this project were to:

    • Estimate the extent of flaxleaf fleabane glyphosate resistance in north east Victoria through a physical survey;
    • Confirm resistance for the survey populations collected and determine the mechanism enabling glyphosate resistance, through biochemical experiments;
    • Investigate the extent of seed dispersal by fleabane to establish how far glyphosate resistance is likely to spread from individual plants within a problem paddock;
    • Examine management of fleabane in mixed farming systems, with a focus on the grazing and herbicide strategies employed in summer fallows and lucerne pastures.

    Knowledge gained from this project will assist with the formulation of strategies to better manage glyphosate resistant flaxleaf fleabane.

    Glyphosate Resistant Flaxleaf FleabaneFlaxleaf fleabane (Conyza bonariensis) populations that are resistant (top row)
    and susceptible (bottom row) to glyphosate (1080 g ai/ha).

  • Biology and management of Chloris truncata (windmill grass) and Chloris virgata (feathertop
    Rhodes grass) in southern Australia
    Duc-The NgoPhD Recipient: The Duc Ngo

    Supervisors: Gurjeet Gill, Christopher Preston and Peter Boutsalis

    Windmill and feathertop Rhodes grasses are emerging weeds in agricultural systems in Australia and there is a need to increase our understanding of their biology and how to manage them best. Improved biological knowledge will help us to predict how these weed species are likely to evolve in response to selection pressures placed on them by current agricultural practices. Studying physiological mechanisms for variations in herbicide sensitivities of windmill and feathertop Rhodes grass populations and biotypes is also valuable.

    The objectives of this project were to:

    • Identify germination characteristics and requirements of windmill grass and feathertop Rhodes grass;
    • Understand their seedling emergence, seed production, seed bank dynamics and seed persistence;
    • Discover variations in glyphosate responses at different plant growth stages, and also within and between populations of these two Chloris species;
    • Identify physiological mechanisms contributing to variations in glyphosate efficacy;
    • Identify optimal glyphosate rates and suitable additives, and also screen for other effective herbicide groups, able to effectively control windmill and feathertop Rhodes grasses.

    Increased understanding in these areas will assist with the development of effective integrated weed management practices that consider these two weedy grasses.

    Windmill grass (Chloris truncata) and Feathertop Rhodes grass (Chloris virgata)Windmill (Chloris truncata) and Feathertop Rhodes (Chloris virgata) grasses growing at Roseworthy, SA.

  • Characterisation and management of herbicide resistance in Hordeum glaucum Steud. (barley grass)
    Lovreet Singh ShergillPhD Recipient: Lovreet Singh Shergill

    Supervisors: Gurjeet Gill, Christopher Preston and Peter Boutsalis

    Barley grass (Hordeum spp.) is an increasingly abundant and problematic weed in South Australian (SA) cropping systems. Recent management practices have led to an increase in seed dormancy in barley grass populations that is broken by exposure to cold temperatures in winter. This means barley grass populations are more frequently establishing after crop sowing. Consequently, reliance on post-emergent herbicides to control barley grass has increased, which in turn has intensified the selection pressure for herbicide resistance.

    This research is designed to identify the extent and mechanisms of resistance to herbicides in barley grass populations, to investigate fitness of resistance alleles, to understand the inheritance of resistance and to identify practices to better manage resistance in this species.

    Findings from this research include:

    • Identification of barley grass populations with high levels of resistance to Group A herbicides; quizalofop at 27–fold, haloxyfop at 15–fold. Target-site mutations in the CT domain of the ACCase gene were found to confer the resistance.
    • Surveys in upper north SA and Eyre Peninsula revealed 14% of smooth barley populations had some level of resistance to quizalofop. Resistance to ALS-inhibiting herbicides was lower (<12%).
    • Seedling recruitment studies showed most smooth barley populations emerged rapidly. No direct link between seed dormancy and herbicide resistance was observed.
    • Field studies indicate PPI propyzamide (Group D), pyroxasulfone (Group K) and post-emergence application of imazamox (Group B) could be effective in the field for managing ACCase-inhibiting herbicide resistant smooth barley.
    • A fitness cost is associated with one of the ACCase target-site mutations in barley grass. When grown in competition with lentils, the herbicide resistant barley grass displayed a reduction in relative growth rate, vegetative biomass and seed production. A different ACCase target-site mutation did not incur a fitness cost although still provided herbicide resistance.

    Knowledge gained from this project will assist with the formulation of strategies to better manage herbicide resistant barley grass.

  • Clethodim resistance in Lolium rigidum (annual ryegrass) and its management
    Rupinder Kaur SainiPhD Recipient: Rupinder Kaur Saini

    Supervisors: Gurjeet Gill, Christopher Preston and Jenna Malone

    Clethodim is a selective post-emergence herbicide used to control annual and perennial grasses in a wide variety of broadleaf crops. Repeated use has resulted in clethodim resistance developing in ryegrass populations.

    This study is designed to identify the mechanisms and inheritance pattern of resistance to clethodim in annual ryegrass, to determine the relative fitness of clethodim-resistant alleles, and to identify effective management strategies for clethodim-resistant weeds.

    Findings from this research include:

    • Clethodim resistant ryegrass populations are spread across Australia and range from 7 to 35-fold resistant
    • Target-site mutations within the ACCase gene occur in some clethodim resistant individuals, but are not the only mechanism of resistance
    • Field trials have shown that many herbicide alternatives to clethodim are not particularly effective. A strategy of pre-emergent herbicide application followed by clethodim works best

    Knowledge gained from this project will assist with the formulation of strategies to slow the rate of clethodim resistance evolution and to manage clethodim-resistant weeds.

    Ryegrass resistance to clethodim

    Response of resistant and susceptible annual ryegrass (Lolium rigidum) populations to different rates of clethodim.

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