Invasive Species Compendium

Detailed coverage of invasive species threatening livelihoods and the environment worldwide

Datasheet

Lolium rigidum
(rigid ryegrass)

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Datasheet

Lolium rigidum (rigid ryegrass)

Summary

  • Last modified
  • 27 September 2018
  • Datasheet Type(s)
  • Invasive Species
  • Pest
  • Host Plant
  • Preferred Scientific Name
  • Lolium rigidum
  • Preferred Common Name
  • rigid ryegrass
  • Taxonomic Tree
  • Domain: Eukaryota
  •   Kingdom: Plantae
  •     Phylum: Spermatophyta
  •       Subphylum: Angiospermae
  •         Class: Monocotyledonae
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    Compendia
    CAB International
    Wallingford
    Oxfordshire
    OX10 8DE
    UK
    compend@cabi.org
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Identity

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Preferred Scientific Name

  • Lolium rigidum Gaudin (1811)

Preferred Common Name

  • rigid ryegrass

International Common Names

  • English: annual ryegrass; stiff darnel; Swiss ryegrass; Wimmera ryegrass
  • Spanish: cizana; raygras rigido
  • French: ivraie raide
  • Portuguese: erva-febra

Local Common Names

  • Germany: Steifer Lolch; Steifes Weidelgras
  • Italy: loglierella

EPPO code

  • LOLRI (Lolium rigidum)

Taxonomic Tree

Top of page
  • Domain: Eukaryota
  •     Kingdom: Plantae
  •         Phylum: Spermatophyta
  •             Subphylum: Angiospermae
  •                 Class: Monocotyledonae
  •                     Order: Cyperales
  •                         Family: Poaceae
  •                             Genus: Lolium
  •                                 Species: Lolium rigidum

Description

Top of page L. rigidum is an annual species forming open tussocks. The dominant habit is erect, but the species is variable in habit, ranging from dense prostrate to more open erect types. Geniculate stems, fibrous root system, up to 1 m high. Reddish-purple colouration at base of stems extends upwards as the plant matures. Leaf blades dark green, hairless, flat, upper surface evenly ribbed, lower surface smooth and shiny, 5-25 cm long, 3-5 mm wide. Young leaves rolled in bud. Auricles small and narrow. Ligule, white, translucent, shorter than wide. Leaf sheath hairless, with fine longitudinal ribs as in leaf blades, reddish-purple at base. Inflorescence is a spike up to 30 cm in length; spikelets edge on to the rachis. Rachis is recessed opposite each spikelet, which more or less fits into the recess. Spikelets of 10-12 florets, laterally flattened, green, 10-25 mm long. Only the terminal spikelet has two more or less equal glumes. Otherwise only one glume subtending each spikelet, lanceloate, 10-15 mm long, two-thirds to three-quarters as long as the spikelet, outer surface fine-veined, ribbed like the upper surface of the leaf blade. No awn. Lemma lanceolate, about 5 mm long, five nerved, usually with no awn, but terminal awns occasionally found, probably as a result of hybridization. Palea similar to lemma in shape and size, two nerves with tiny hairs along them. Anthers three, yellow.

Plant Type

Top of page Annual
Grass / sedge
Seed propagated

Distribution

Top of page L. rigidum is native to the Mediterranean region.

Distribution Table

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The distribution in this summary table is based on all the information available. When several references are cited, they may give conflicting information on the status. Further details may be available for individual references in the Distribution Table Details section which can be selected by going to Generate Report.

Continent/Country/RegionDistributionLast ReportedOriginFirst ReportedInvasiveReferenceNotes

Asia

AfghanistanPresentNativeUSDA-ARS, 1998
ArmeniaPresentNativeUSDA-ARS, 1998
AzerbaijanPresentNativeUSDA-ARS, 1998
Georgia (Republic of)PresentNativeUSDA-ARS, 1998
IndiaPresentNativeHolm et al., 1991
IranPresentNativeUSDA-ARS, 1998
IraqPresentNativeHolm et al., 1991; USDA-ARS, 1998
IsraelPresentNativeHolm et al., 1991; USDA-ARS, 1998
JordanPresentNativeUSDA-ARS, 1998
KuwaitPresentNativeUSDA-ARS, 1998
LebanonPresentNativeHolm et al., 1991; USDA-ARS, 1998
PakistanPresentNativeUSDA-ARS, 1998
Saudi ArabiaPresentNativeChaudhary and Akram, 1987
SyriaPresentNativeUSDA-ARS, 1998
Turkey-in-AsiaPresentNativeUSDA-ARS, 1998
TurkmenistanPresentNativeUSDA-ARS, 1998
UzbekistanPresentNativeUSDA-ARS, 1998

Africa

AlgeriaPresentNativeUSDA-ARS, 1998
EgyptPresentNativeUSDA-ARS, 1998
LibyaPresentNativeUSDA-ARS, 1998
MoroccoPresentNativeHolm et al., 1991; USDA-ARS, 1998
South AfricaPresentIntroducedHolm et al., 1991
TunisiaWidespreadNativeHolm et al., 1991; USDA-ARS, 1998

North America

MexicoPresentIntroduced
USAPresentPresent based on regional distribution.
-ArizonaPresentIntroducedUSDA, 2004
-CaliforniaPresentIntroducedUSDA, 2004
-HawaiiPresentIntroducedHolm et al., 1991
-LouisianaPresentIntroducedUSDA, 2004
-MissouriPresentIntroducedUSDA, 2004
-OregonPresentIntroducedUSDA, 2004
-TexasPresentIntroducedUSDA, 2004

South America

ArgentinaPresent
ChilePresentIntroducedHeap, 2004

Europe

AlbaniaPresentNativeUSDA-ARS, 1998
BulgariaPresentNativeUSDA-ARS, 1998
FrancePresentIntroducedUSDA-ARS, 1998
-CorsicaPresentIntroducedUSDA-ARS, 1998
GreecePresentNativeUSDA-ARS, 1998
ItalyPresentNativeUSDA-ARS, 1998
PortugalPresentNativeHolm et al., 1991; USDA-ARS, 1998
Russian FederationPresentNativeKutuzov and Truzina, 1990
SpainPresentNativeUSDA-ARS, 1998; Cirujeda et al., 2011
SwitzerlandPresentNativeUSDA-ARS, 1998
UkrainePresentNativeUSDA-ARS, 1998
Yugoslavia (former)PresentNativeUSDA-ARS, 1998

Oceania

AustraliaWidespreadIntroducedHolm et al., 1991
-New South WalesPresentIntroducedLazarides et al., 1997
-QueenslandPresentIntroducedLazarides et al., 1997
-South AustraliaPresentIntroducedLazarides et al., 1997
-TasmaniaPresentIntroducedLazarides et al., 1997
-VictoriaPresentIntroducedLazarides et al., 1997
-Western AustraliaPresentIntroducedLazarides et al., 1997

History of Introduction and Spread

Top of page L. rigidum is native to Mediterranean countries of southern Europe and North Africa, to the Asian Gulf and Indian sub-continent. It has been introduced or spread to North and South America, South Africa and Australia. It was intentionally introduced to Australia as a desirable pasture species during the 19th Century and has since become a serious cropping weed across southern Australia. It is easily spread as a contaminant of certified and farmer-retained crop seed and has often been found as a contaminant of Australian crop seed (Niknam et al., 2002).

Habitat List

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CategoryHabitatPresenceStatus
Terrestrial-managed
Cultivated / agricultural land Present, no further details Harmful (pest or invasive)
Disturbed areas Present, no further details Harmful (pest or invasive)
Managed forests, plantations and orchards Present, no further details Harmful (pest or invasive)
Rail / roadsides Present, no further details Harmful (pest or invasive)

Biology and Ecology

Top of page Genetics

L. rigidum is a self-incompatible, outcrossing diploid species with a chromosome number of n=7 (2n=14). It displays a high degree of genetic variability, enabling it to rapidly adapt to a range of climatic, edaphic and agricultural situations (Kloot, 1983). In Australia, L. rigidum populations with large differences in phenological development have been documented, demonstrating adaptation to local environments since the species introduction to that continent (Gill et al., 1996). It also exhibits considerable phenotypic plasticity (Gill et al., 1996). L. rigidum is able to freely hybridize with L. multiflorum and L. perenne and can form intergeneric hybrids with a numer of Festuca species (Terrell, 1968). Electrophoretic and morphological studies have been able to differentiate between Lolium species, although considerable introgression between species, particularly L. rigidum and L. multiflorum, was evident (Bennett et al., 2000, 2002). In a study of Lolium species from Italy, 40-60% of individuals were hybrids (Dinelli et al., 2002). Balfourier et al. (2000) found a high level of within-population variation in L. rigidum and found that pollen-mediated gene flow between populations was 2.2 times greater than gene flow by seed movement.

Physiology and Phenology

Freshly dispersed L. rigidum seeds display innate dormancy, requiring a period of after-ripening to germinate. Dormancy release in populations from Western Australia has been shown to be directly related to accumulated temperature following maturation with some variation noted in the degree of dormancy at the time of dispersal between different populations (Steadman et al., 2003). An alternative mechanism of L. rigidum dormancy release has also been proposed by Steadman (2002) who showed that seeds respond to hydration in darkness. A portion of seeds may display enforced dark dormancy (10-20%) (Gramshaw and Stearn, 1977) leading to short-term persistance of buried seeds. Pearce and Quinlivan (1971) found optimum germination and seedling emergence in seed buried close to the soil surface and Gramshaw and Stearn (1977) reported decreasing establishment of seed buried below this depth with complete inhibition at depths of 11-14 cm. Peltzer and Matson (2002) reported an annual seed bank decline of 70-80% for L. rigidum. Similar results were reported in Spain by Fernandez-Quintanilla et al. (2000) with average annual recruitment from the seed bank of 67% and high seedling survival (78-95%) in most environments.

L. rigidum is an annual grass which reproduces solely by seed. It is highly competitive with crops and is a prolific seed producer. Rerkasem et al. (1980) reported seed production figures of 31,000-45,000 seeds per m² in a wheat crop.

Associations

L. rigidum inflorescences infected with the plant pathogen Clavibacter sp. can cause mortality to livestock due to the ingestion of corynetoxins. In Australia, between 1968 and 1999, annual ryegrass toxicity resulted in the deaths of an estimated 147,000 sheep and 500 cattle (Gill, 1995). Control of annual ryegrass toxicity is largely dependent on control of the host. L. rigidum is also quite susceptible to ergot fungus (Claviceps purpurea) which can lead to the downgrading of infected grain as this fungus is toxic to man and animals. Lolium sp. are also thought to be susceptible to the take-all fungus (Gaeumannomyces graminis) (Cotterill and Sivasithamparam, 1988) and can hence contribute to soil inoculum levels of this serious disease of cereal crops.

Air Temperature

Top of page
Parameter Lower limit Upper limit
Mean maximum temperature of hottest month (ºC) 20 35
Mean minimum temperature of coldest month (ºC) 10 20

Rainfall

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ParameterLower limitUpper limitDescription
Mean annual rainfall3001000mm; lower/upper limits

Rainfall Regime

Top of page Winter

Soil Tolerances

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Soil drainage

  • free
  • impeded

Soil reaction

  • acid
  • alkaline
  • neutral

Soil texture

  • heavy
  • light
  • medium

Special soil tolerances

  • infertile
  • saline

Notes on Natural Enemies

Top of page There are no reports on the natural enemies of L. rigidum. There have been few investigations into the potential for biological control of L. rigidum due to its value as a forage species.

Means of Movement and Dispersal

Top of page L. rigidum may be moved by agricultural machinery or as a contaminant of commercial crop seed (see section on History of Introduction and Spread).

Plant Trade

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Plant parts liable to carry the pest in trade/transportPest stagesBorne internallyBorne externallyVisibility of pest or symptoms
Bulbs/Tubers/Corms/Rhizomes seeds Yes Pest or symptoms usually invisible
Growing medium accompanying plants seeds Yes Pest or symptoms usually invisible
Roots seeds Yes Pest or symptoms usually invisible
Seedlings/Micropropagated plants seeds Yes Pest or symptoms usually invisible
True seeds (inc. grain) seeds Yes Pest or symptoms usually visible to the naked eye
Plant parts not known to carry the pest in trade/transport
Bark
Flowers/Inflorescences/Cones/Calyx
Fruits (inc. pods)
Leaves
Stems (above ground)/Shoots/Trunks/Branches
Wood

Wood Packaging

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Wood Packaging not known to carry the pest in trade/transport
Loose wood packing material
Non-wood
Processed or treated wood
Solid wood packing material with bark
Solid wood packing material without bark

Impact Summary

Top of page
CategoryImpact
Animal/plant collections None
Animal/plant products None
Biodiversity (generally) None
Crop production None
Environment (generally) None
Fisheries / aquaculture None
Forestry production None
Human health None
Livestock production None
Native fauna None
Native flora None
Rare/protected species None
Tourism None
Trade/international relations None
Transport/travel None

Risk and Impact Factors

Top of page Invasiveness
  • Invasive in its native range
  • Proved invasive outside its native range
  • Highly adaptable to different environments
  • Tolerates, or benefits from, cultivation, browsing pressure, mutilation, fire etc
  • Highly mobile locally
  • Has high reproductive potential
  • Has propagules that can remain viable for more than one year
Impact outcomes
  • Negatively impacts agriculture
  • Negatively impacts human health
  • Negatively impacts animal health
Impact mechanisms
  • Competition - monopolizing resources
  • Pest and disease transmission
Likelihood of entry/control
  • Highly likely to be transported internationally accidentally
  • Difficult/costly to control

Uses List

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Materials

  • Poisonous to mammals

Similarities to Other Species/Conditions

Top of page A number of related species can occur as weeds - see datasheet on Lolium multiflorum. Note that L. perenne is similar in having no awns, but the glume is much shorter than the spikelet.

Prevention and Control

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Mechanical Control

Shallow cultivation early in the growing season, prior to crop sowing, has the potential to stimulate germination of L. rigidum, although this practice is not so successful on heavier soils. Reeves and Smith (1975) showed that mouldboard ploughing reduced L. rigidum numbers more than disc ploughing, and Matthews et al. (1996) reported a reduction of L. rigidum numbers in the following crop of 98% after mouldboard ploughing.

Cultural Control

A number of cultural practices can be used to contribute to L. rigidum control. Initial germination of L. rigidum following autumn rainfall is believed to account for about 60-80% of total seasonal emergence. Given this fact, it is possible to delay crop sowing in order to control the majority of L. rigidum before crop establishment (Gill, 1995). This practice may result in reduced crop yielding potential. Planes et al. (1999) showed that a delay in wheat sowing decreased the L. rigidum seed bank by 40% and seedling density by 27%. However, delayed seeding resulted in yield loss of 46 kg/ha/day. Increasing crop competition by increasing sowing rates and selection and breeding of competitive crop cultivars has also been advocated. Medd et al. (1985) reported that ryegrass numbers were unaffected by increased wheat crop density but that potential L. rigidum seed production was reduced. Similarly, Matthews (2002) reported that L. rigidum fecundity was reduced at high crop densities. Lemerle et al. (2001) showed significant differences in the competitive abilities of wheat cultivars against ryegrass and other research has identified quantitative trait loci for traits conferring greater competitiveness in wheat (Coleman et al., 2001). It is anticipated that quantitative trait loci can be used in marker assisted breeding programmes in the future. Studies in Australia have demonstrated the potential for capture and collection of L. rigidum seeds during the harvest operation (Matthews et al., 1996) and this practice is widely used where herbicide resistance has become a severe problem. Once collected, this seed can be dumped in piles in the field and burnt or removed and destroyed to considerably reduce the L. rigidum seed bank. Burning of stubbles, where permitted, has the potential to kill L. rigidum seeds at the soil surface.

The seed heads of L. rigidum are preferentially grazed by cattle and sheep, thereby reducing total seed production and seed bank replenishment. Following ingestion and excretion of L. rigidum seed by cattle and sheep, only 11.9 and 3.9% of seeds, respectively, were germinable (Stanton et al., 2002).

Chemical Control

Mamarot and Rodriguez (1997) give recommendations for herbicide use against Lolium species, including L. rigidum, in a range of crops; carbetamide in legumes, rape and sunflower; EPTC and atrazine in maize; monolinuron in potato; and a range of herbicides related to sethoxydim and fluazifop in broad-leaved crops.

The development of widespread and multiple resistance to a range of herbicide classes has been widely reported in L. rigidum populations. Resistance has been reported to simazine (Gonzalez-Guttierez and Prado, 1997), diclofop-methyl, chlortoluron and isoproturon (Prado et al., 1997), carbetamide (Hole and Powles, 1997), triasulfuron, sulfometuron and imazethapyr (Gill, 1995) and metolachlor (Burnet et al., 1994a). In one population, resistance to nine herbicide classes was found (Burnet et al., 1994b) and recently a population with resistance to glyphosate has been reported making L. rigidum the first weed to develop such resistance (Gut, 1998; Powles et al., 1998). To 2004, L. rigidum populations resistant to ACCase inhibitors, ALS inhibitors, dinitroalinines, triazoles, ureas, isoxazolidiones, mitosis inhibitors, chloracetamides, thiocarbamates, photosystem II inhibitors and glycines have been reported in Australia. Resistance to ACCase inhibitors has also been reported in Chile, France, Greece, Israel, Saudi Arabia, South Africa, Spain and Tunisia, to ALS inhibitors in South Africa, to photosystem II inhibitors in Israel and Spain, to glyphosate in South Africa and the USA and to bipyridiliums in South Africa (Heap, 2004). L. rigidum is ranked as the world's most herbicide-resistance-prone weed (Heap, 2004).

Integrated Management

The rapid and widespread development of resistance in L. rigidum necessitates the formulation of integrated weed management strategies which will reduce the reliance on chemical control and delay or avoid the widespread evolution of resistance. Integrated management should involve delayed crop seeding date, the planting of competitive crop varieties, the use of non-selective herbicides, collection of weed seed at harvest and introducing pasture phases into crop rotations (Powles and Matthews, 1996; Gill and Holmes, 1997).

References

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Balfourier F; Imbert C; Charmet G, 2000. Evidence for phylogeographic structure in Lolium species related to the spread of agriculture in Europe. A cpDNA study. Theoretical and Applied Genetics, 101:131-138.

Bennett SJ; Hayward MD; Marshall DF, 2000. Morphological differentiation in four species of the genus Lolium. Genetic Resources and Crop Evolution. 47(3):247-255.

Bennett SJ; Hayward MD; Marshall DF, 2002. Electrophoretic variation as a measure of species differentiation between four species of the genus Lolium. Genetic Resources and Crop Evolution, 49(1):59-66.

Burnet MWM; Barr AR; Powles SB, 1994. Chloroacetamide resistance in rigid ryegrass (Lolium rigidum). Weed Science, 42(2):153-157.

Burnet MWM; Hart Q; Holtum JAM; Powles SB, 1994. Resistance to nine herbicide classes in a population of rigid ryegrass (Lolium rigidum). Weed Science, 42(3):369-377.

Chaudhary SA; Akram M, 1987. Weeds of Saudi Arabia and the Arabian Peninsula. Saudi Arabia: National Herbarium, Regional Agriculture and Water Research Center, Ministry of Agriculture and Water.

Cirujeda A; Aibar J; Zaragoza C, 2011. Comparison of weed flora in winter cereals in the province of Zaragoza (Spain) from 1976 and thirty years later. (Comparación de la flora arvense en cereal de invierno en la provincia de Zaragoza entre 1976 y 2005-07.) In: Plantas invasoras resistencias a herbicidas y detección de malas hierbas. XIII Congreso de la Sociedad Española de Malherbología, La Laguna, Spain, 22-24 November 2011 [ed. by Arévalo, J. R.\Fernández, S.\López, F.\Recasens, J.\Sobrino, E.]. Madrid, Spain: Sociedad Española de Malherbología (Spanish Weed Science Society), 203-206.

Coleman RK; Gill GS; Rebetzke GJ, 2001. Identification of quantitative trait loci for traits conferring weed competitiveness in wheat (Triticum aestivum L.). Australian Journal of Agricultural Research, 52(11/12):1235-1246; 39 ref.

Cotterill PJ; Sivasithamparam K, 1988. Importance of the proportion of grassy weeds within legume crops in the perpetuation of Gaeumannomyces graminis var. tritici. Plant Pathology, 37(3):337-343

Davidson RM, 1990. Management of herbicide resistant annual ryegrass Lolium rigidum. M.Ag.Sc. thesis, LaTrobe University, Melbourne, Australia.

Dinelli G; Bonetti A; Lucchese C; Catizone P; Bravin F; Zanin G, 2002. Taxonomic evaluation of Italian populations of Lolium spp. resistant and susceptible to diclofop-methyl. Weed Research (Oxford), 42(2):156-165; 40 ref.

Fernandez-Quintanilla C; Barroso J; Recasens J; Sans X; Torner C; Sanchez del Arco MJ, 2000. Demography of Lolium rigidum in winter barley crops: analysis of recruitment, survival and reproduction. Weed Research (Oxford), 40(3):281-291; 20 ref.

Gill GS, 1995. Development of herbicide resistance in annual ryegrass populations (Lolium rigidum Gaud.) in the cropping belt of Western Australia. Australian Journal of Experimental Agriculture, 35(1):67-72.

Gill GS; Dowling P; Medd R, 1996. Ecology of annual ryegrass. Wild oats, annual ryegrass and Vulpia. Proceedings of a workshop held at Orange, New South Wales, Australia. Plant Protection Quarterly, 11:198-200.

Gill GS; Holmes JE, 1997. Efficacy of control methods for combating herbicide resistant Lolium rigidum. Resistance '97. Integrated approach to combating resistance. Pesticide Science, 51(3):352-358.

Gonzalez-Guttierez J; Prado R de, 1997. Control of a simazine resistant Lolium rigidum biotype at low rates of different glyphosate formulations. Proceedings of the 1997 Congress of the Spanish Weed Science Society, Valencia, Spain. Madrid, Spain: Sociedad Espanola de Malherbologia, 83-87.

Gramshaw D; Stearn WR, 1977. Survival of annual reygrass (Lolium rigidum Gaud.) seed in a Mediterranean type environment. II. Effects of short term burial on persistance of viable seed. Australian Journal of Agricultural Research, 28:93-101.

Gut D, 1998. First weed resistant to glyphosate. Obst- und Weinbau, 134(8):223-224; 5 ref.

Heap I, 2004. International survey of herbicide resistant weeds. http://www.weedscience.org/in.asp.

Hole SJW; Powles SB, 1997. Reduced efficacy and enhanced degradation of carbetamide after repeated application in Australia. Weed Research (Oxford), 37(3):165-170; 5 ref.

Holm LG; Pancho JV; Herberger JP; Plucknett DL, 1991. A Geographic Atlas of World Weeds. Malabar, Florida, USA: Krieger Publishing Company.

Kloot PM, 1983. The genus Lolium in Australia. Australian Journal of Botany, 31:421-435.

Kutuzov GP; Truzina LA, 1990. Herbicides on annual ryegrass crops undersown with perennial grasses. Zashchita Rastenii (Moskva), No. 4:29-30.

Lazarides M; Cowley K; Hohnen P, 1997. CSIRO handbook of Australian weeds. CSIRO handbook of Australian weeds., vii + 264 pp.

Lemerle D; Verbeek B; Orchard B, 2001. Ranking the ability of wheat varieties to compete with Lolium rigidum. Weed Research (Oxford), 41(3):197-209; 26 ref.

Mamarot J; Rodriguez A, 1997. Sensibilité des Mauvaises Herbes aux Herbicides. 4th edition. Paris, France: Association de Coordination Technique Agricole.

Matthews J, 2002. Broadcast sowing, crop row spacing and crop density for the suppression of ryegrass in wheat rotations. 13th Australian Weeds Conference: weeds "threats now and forever?", Sheraton Perth Hotel, Perth, Western Australia, 8-13 September 2002: papers and proceedings, 709-711; 3 ref.

Matthews J; Llewellyn R; Reeves TG and Powles SB, 1996. Integrated management for the control of herbicide resistant ryegrass. Proceedings of the 8th Australian Agronomy Conference, Toowoomba, Australia, 417-420.

Medd RW; Auld BA; Kemp DR; Murison RD, 1985. The influence of wheat density and spatial arrangement on annual ryegrass, Lolium rigidum Gaudin, competition. Australian Journal of Agricultural Research, 36(3):361-371

Niknam SR; Moerkerk M; Cousens R, 2002. Weed seed contamination in cereal and pulse crops. 13th Australian Weeds Conference: weeds "threats now and forever?", Sheraton Perth Hotel, Perth, Western Australia, 8-13 September 2002: papers and proceedings, 59-62; 3 ref.

Pearce GA; Quinlivan BJ, 1971. The control of annual (’Wimmera’) ryegrass in cereal crops. Journal of Agriculture, Western Australia, 12:58:62.

Peltzer SC; Matson PT, 2002. How fast do the seedbanks of five annual cropping weeds deplete in the absence of weed seed input?. 13th Australian Weeds Conference: weeds "threats now and forever?", Sheraton Perth Hotel, Perth, Western Australia, 8-13 September 2002: papers and proceedings, 553-555; 12 ref.

Planes J; Brieno R; Recasens J, 1999. Does the cereal sowing date influence in the management of herbicide-resistant Lolium rigidum populations ? SEMh Congresso 1999: Sociedad Espanola de malherbologia, Actas, Logrono, Spain. Departamento Hortofruticultura, Botanica I Jardineria, Lerida, Spain, 397-393.

Powles SB; Lorraine-Colwill DF; Dellow JJ; Preston C, 1998. Evolved resistance to glyphosate in rigid ryegrass (Lolium rigidum) in Australia. Weed Science, 46(5):604-607; 24 ref.

Powles SB; Matthews JM, 1996. Integrated weed management for the control of herbicide resistant annual ryegrass (Lolium rigidum). Proceedings of the 2nd International Weed Control Congress, Copenhagen, Denmark. Slagelse, Denmark: Department of Weed Control and Pesticide Ecology, 407-414.

Prado Rde; Prado JLde; MenTndez J, 1997. Resistance to substituted urea herbicides in Lolium rigidum biotypes. Pesticide Biochemistry and Physiology, 57(2):126-136; 36 ref.

Reeves TG; Smith IS, 1975. Pasture management and cultural methods for the control of annual ryegrass (Lolium rigidum) in wheat. Australian Journal of Experimental Agriculture and Animal Husbandry, 15(75):527-530

Rerkasem K; Stern WR; Goodchild NA, 1980. Associated growth of wheat and annual ryegrass. I. Effect of varying total density and proportion in mixtures of wheat and annual ryegrass. Australian Journal of Agricultural Resarch, 31:649-658.

Stanton R; Piltz J; Pratley J; Kaiser A; Hudson D; Dill G, 2002. Annual ryegrass (Lolium rigidum) seed survival and digestibility in cattle and sheep. Australian Journal of Experimental Agriculture, 42(2):111-115; 14 ref.

Steadman KJ, 2002. A summary of dormancy in annual ryegrass (Lolium rigidum) seeds: dry after-ripening versus imbibition in the dark. 13th Australian Weeds Conference: weeds "threats now and forever?", Sheraton Perth Hotel, Perth, Western Australia, 8-13 September 2002: papers and proceedings, 468-470; 5 ref.

Steadman KJ; Crawford AD; Gallagher RS, 2003. Dormancy release in Lolium rigidum seeds is a function of thermal after-ripening time and seed water content. Functional Plant Biology, 30(3):345-352; 31 ref.

Terrell E, 1968. A taxonomic revision of the genus Lolium. Technical Bulletin of the USDA 1392:1-65.

USDA, 2004. Natural Resources Conservation Service. Plant profiles - Lolium. http://plants.usda.gov/cgi_bin/plant_profile.cgi?symbol=LOLIU.

USDA-ARS, 1999. Germplasm Resources Information Network (GRIN). Online Database. Beltsville, Maryland, USA: National Germplasm Resources Laboratory. https://npgsweb.ars-grin.gov/gringlobal/taxon/taxonomysearch.aspx

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