Invasive Species Compendium

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Datasheet

Emex australis
(Doublegee)

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Datasheet

Emex australis (Doublegee)

Summary

  • Last modified
  • 27 September 2018
  • Datasheet Type(s)
  • Invasive Species
  • Pest
  • Host Plant
  • Preferred Scientific Name
  • Emex australis
  • Preferred Common Name
  • Doublegee
  • Taxonomic Tree
  • Domain: Eukaryota
  •   Kingdom: Plantae
  •     Phylum: Spermatophyta
  •       Subphylum: Angiospermae
  •         Class: Dicotyledonae
  • Summary of Invasiveness
  • The thorny achenes of E. australis give the plant its invasive properties, which can travel impaled on rubber tyres or as contaminants of agriculture produce for long distances and seeds remain viable for over 8 years in the soil. It is predominantly...

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Pictures

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PictureTitleCaptionCopyright
(a) Achenes from crown (subterranean), (b) achenes from crown (above soil surface) and (c) aerial achenes. Sequence from top to bottom of column: 1) mature, 2) immature sectioned, 3) immature.
TitleAchenes
Caption(a) Achenes from crown (subterranean), (b) achenes from crown (above soil surface) and (c) aerial achenes. Sequence from top to bottom of column: 1) mature, 2) immature sectioned, 3) immature.
CopyrightPaul B. Yeoh/CSIRO
(a) Achenes from crown (subterranean), (b) achenes from crown (above soil surface) and (c) aerial achenes. Sequence from top to bottom of column: 1) mature, 2) immature sectioned, 3) immature.
Achenes(a) Achenes from crown (subterranean), (b) achenes from crown (above soil surface) and (c) aerial achenes. Sequence from top to bottom of column: 1) mature, 2) immature sectioned, 3) immature.Paul B. Yeoh/CSIRO
E. australis rosette showing the well developed taproot and early formation of achenes. These attributes give the species some drought-proofing, enabling it to survive 'false breaks'.
TitleRosette
CaptionE. australis rosette showing the well developed taproot and early formation of achenes. These attributes give the species some drought-proofing, enabling it to survive 'false breaks'.
CopyrightPaul B. Yeoh/CSIRO
E. australis rosette showing the well developed taproot and early formation of achenes. These attributes give the species some drought-proofing, enabling it to survive 'false breaks'.
RosetteE. australis rosette showing the well developed taproot and early formation of achenes. These attributes give the species some drought-proofing, enabling it to survive 'false breaks'.Paul B. Yeoh/CSIRO
Emex australis (a) and E. spinosa (b) both grown for 20 weeks under identical glasshouse conditions. If able to be supported by other vegetation, E. australis will grow semi-erect (as in this photo) rather than prostrate.
TitleHabit
CaptionEmex australis (a) and E. spinosa (b) both grown for 20 weeks under identical glasshouse conditions. If able to be supported by other vegetation, E. australis will grow semi-erect (as in this photo) rather than prostrate.
CopyrightPaul B. Yeoh/CSIRO
Emex australis (a) and E. spinosa (b) both grown for 20 weeks under identical glasshouse conditions. If able to be supported by other vegetation, E. australis will grow semi-erect (as in this photo) rather than prostrate.
HabitEmex australis (a) and E. spinosa (b) both grown for 20 weeks under identical glasshouse conditions. If able to be supported by other vegetation, E. australis will grow semi-erect (as in this photo) rather than prostrate.Paul B. Yeoh/CSIRO
E. australis achenes and flowers.
TitleAchenes and flowers
CaptionE. australis achenes and flowers.
CopyrightPaul B. Yeoh/CSIRO
E. australis achenes and flowers.
Achenes and flowersE. australis achenes and flowers.Paul B. Yeoh/CSIRO
E. australis crown and taproot region.
TitleCrown and taproot
CaptionE. australis crown and taproot region.
CopyrightPaul B. Yeoh/CSIRO
E. australis crown and taproot region.
Crown and taprootE. australis crown and taproot region.Paul B. Yeoh/CSIRO
Dense infestation of E. australis in the pasture phase of a pasture/cereal rotation farming system in Western Australia.
TitleInfestation
CaptionDense infestation of E. australis in the pasture phase of a pasture/cereal rotation farming system in Western Australia.
CopyrightPaul B. Yeoh/CSIRO
Dense infestation of E. australis in the pasture phase of a pasture/cereal rotation farming system in Western Australia.
InfestationDense infestation of E. australis in the pasture phase of a pasture/cereal rotation farming system in Western Australia.Paul B. Yeoh/CSIRO
A large, mature, prostrate E. australis plant growing on the edge of a wheat crop.
TitleHabit
CaptionA large, mature, prostrate E. australis plant growing on the edge of a wheat crop.
CopyrightPaul B. Yeoh/CSIRO
A large, mature, prostrate E. australis plant growing on the edge of a wheat crop.
HabitA large, mature, prostrate E. australis plant growing on the edge of a wheat crop.Paul B. Yeoh/CSIRO
The tough spines of the E. australis achene enable long distance movement on car tyres. The E. australis plants surrounding the tyre are growing in the pasture phase of a pasture/cereal rotation farming system in Western Australia.
TitleSeed transport
CaptionThe tough spines of the E. australis achene enable long distance movement on car tyres. The E. australis plants surrounding the tyre are growing in the pasture phase of a pasture/cereal rotation farming system in Western Australia.
CopyrightJohn K. Scott/CSIRO
The tough spines of the E. australis achene enable long distance movement on car tyres. The E. australis plants surrounding the tyre are growing in the pasture phase of a pasture/cereal rotation farming system in Western Australia.
Seed transportThe tough spines of the E. australis achene enable long distance movement on car tyres. The E. australis plants surrounding the tyre are growing in the pasture phase of a pasture/cereal rotation farming system in Western Australia.John K. Scott/CSIRO

Identity

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Preferred Scientific Name

  • Emex australis Steinh.

Preferred Common Name

  • Doublegee

Other Scientific Names

  • Emex centropodium Meisner
  • Vibro australis Greene

International Common Names

  • English: bindii; bull head; cape spinach; Cathead; cat's head; Devil's-thorn; Emex; giant bull head; goat head; prickly jack; southern three corner jack; Spiny emex; tanner's curse; three-cornered jack

Local Common Names

  • Germany: Suedliche Emex
  • South Africa: dubbeltiedorings; Duwweltjie; Emex-dubbeltjie; Inkunzane

EPPO code

  • EMEAU (Emex australis)

Summary of Invasiveness

Top of page The thorny achenes of E. australis give the plant its invasive properties, which can travel impaled on rubber tyres or as contaminants of agriculture produce for long distances and seeds remain viable for over 8 years in the soil. It is predominantly a weed of agriculture and pasture and can greatly reduce crop yields. In Australia, it may infest over 2 million ha of pasture and 1 million ha of cereal crops. In order to restrict the plant's introduction or spread via human intervention, E. australis is declared noxious in several countries including Australia, USA, Japan and New Zealand.

Taxonomic Tree

Top of page
  • Domain: Eukaryota
  •     Kingdom: Plantae
  •         Phylum: Spermatophyta
  •             Subphylum: Angiospermae
  •                 Class: Dicotyledonae
  •                     Order: Polygonales
  •                         Family: Polygonaceae
  •                             Genus: Emex
  •                                 Species: Emex australis

Notes on Taxonomy and Nomenclature

Top of page The type specimen for Emex australis Steinheil (1838) was collected from the Cape of Good Hope, South Africa. The genus name Emex is thought to be derived from Rumex, the genus to which it was originally placed and the Latin word 'ex', (out of) (Shivas and Sivasithamparam, 1994). The species name, australis, is Latin for 'southern' and refers to its southern African origins.

The common name most frequently used in Australia, doublegee, is derived from dubbeltjie, an Afrikaans word meaning devil's thorn (Gilbey, 1975; Gilbey and Weiss, 1980). It was also known as Cape spinach as the young leaves are palatable and can be eaten as spinach (Gardner, 1930); however, soon after being imported into Australia, the plant became troublesome and was more likely to be referred to as tanner's curse (Gilbey, 1975). Common names incorporating the word "jack" presumably refer to the children's game in which small 6-pointed metal pieces are picked up whilst bouncing a ball. Other common names such as cat's head, bull head, devil's thorn and goat head are presumably based upon the visual resemblance of the achene, when viewed from the side so that only two of the three spines are showing, to an animal/devil head with the spines on the achene being the horns/ears.

Description

Top of page E. australis is an annual that can only reproduce by seed (Gilbey and Weiss, 1980). Cotyledons are hairless and shaped like an elongated club with a round apex. The first leaves produced are hairless and oval with an obtuse apex. All subsequent leaves are more triangular with an indented, heart-shaped base (Wilding et al., 1993). The plant develops a long and thick taproot. The adult plant is prostrate or ascending with round, ribbed stems that radiate from the crown in all directions and that branch dichotomously at nodes. On the stems, at the base of the petioles, are brown membranous ochreae (circa 5 mm long). The basal leaves are usually the longest leaves on the plant (up to 15 cm) and have similarly long petioles. Moving along the stem and away from the crown, the leaves become smaller (down to 3 cm) with shorter petioles. The small (circa 2 mm), inconspicuous green flowers have separate sexes but are self-compatible and from these a hard wooden achene (fruit) with three spines (=modified lobes of the perianth) develops (Gardner, 1930). Achenes are dimorphic. Those attached to the lower sections of the crown of the plant (subterranean) differ from those attached elsewhere, including the upper sections of the crown (aerial), in that they are flattened with a bilateral rather than radial symmetry and they have proportionally shorter spines. Achenes are originally green (aerial) or white with yellow and red (subterranean) but turn brown as they ripen. The ripe subterranean achenes tend to remain attached to the mother plant's crown even after the plant has senesced and in subsequent years are likely to germinate near its parental plant's location (Gilbey and Weiss, 1980). The ripe aerial achenes readily detach from the parental plant and are triangular in cross section with their spines arranged so that one spine always points upwards, thereby increasing their chance of dispersal via a passing animal or even vehicles. Typically, only the aerial achenes are noticed as they are far more numerous, are on the soil's surface and have the strong, sharp, impaling spines. A similar achene dimorphism occurs in E. spinosa (Evenari et al., 1977; Weiss, 1980).

The achenes contain a single, trigonous seed, produced firstly in the rosette and then sequentially in leaf axils along the stems. The plant has indeterminate growth, with stem and seed production continuing as long as the season is favourable. They ripen in approximately the same order as conception so that green achenes are still developing near the growing apices of the stem whilst ripe achenes have been shed from the stem near the crown. Due to the continuous growing nature of the plant, the size of aerial achenes vary greatly even within a single plant, but achenes are commonly >10 mm wide (spine tip to spine tip). In E. australis the subterranean achenes rarely exceed 8 mm wide (spine tip to spine tip). Weiss and Simmons (1979) collected seed (achenes) from E. australis populations in its native South Africa as well as from Australia and Hawaii where it is an exotic. Two generations of plant were then grown from these seeds planted simultaneously and within the same glasshouse, so as to remove the effects of environmental variations. They found little difference between the Australian and South African populations of E. australis, but second-generation plants from the Hawaii population had fewer stems, nodes and leaves and produced 40% less seeds than the others. Scott (1990) studied the biology and population dynamics of E. australis growing in South Africa and compared this to similar data collected by Weiss (1981) for E. australis grown in Australia. Seed banks, seedling densities, survivorship data and achene production were all found to be similar.

Plant Type

Top of page Annual
Broadleaved
Herbaceous
Seed propagated

Distribution

Top of page E. australis is a native of South Africa, possibly restricted to the south-west and south-east regions (Smith, 1966) though several authors (e.g. USDA-ARS, 2003) note the native range as including South Africa, Swaziland, Lesotho and Namibia. It has been widely introduced and is clearly continuing to be introduced, noted by interceptions in Japan (Kurokawa, 2001) although the UK (Louseley and Kent, 1981) and the species has not been reported as established in these locations.

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

IndiaPresentIntroducedbefore 1838Steinheil, 1838
PakistanPresent, few occurrencesIntroduced Not invasive Siddiqi, 1973
TaiwanRestricted distributionEPPO, 2014

Africa

BotswanaWidespreadIntroducedFox and Young, 1982; Wells et al., 1986
KenyaRestricted distributionIntroducedGraham, 1958; Terry and Michieka, 1987; EPPO, 2014
LesothoPresentNativeGuillarmod, 1971; Wells et al., 1986; USDA-ARS, 2003
MadagascarPresent, few occurrencesIntroducedbefore 1838Steinheil, 1838
MalawiPresent, few occurrencesIntroducedBinns, 1968
MauritiusPresent, few occurrencesIntroducedHolm et al., 1979
NamibiaWidespreadNativeMerxmuller, 1969; Fox and Young, 1982; Wells et al., 1986; USDA-ARS, 2003
Saint HelenaPresentPresent based on regional distribution.
-AscensionPresentIntroducedSteinheil, 1838
South AfricaRestricted distributionNative Invasive Smith, 1966; USDA-ARS, 2003; EPPO, 2014
TanzaniaPresentIntroducedMissouri Botanic Garden, 2003
ZambiaPresentIntroducedTerry and Michieka, 1987
ZimbabweRestricted distributionEPPO, 2014

North America

USAWidespreadEPPO, 2014
-CaliforniaRestricted distributionIntroducedRobbins et al., 1951; USDA-ARS, 2003
-HawaiiPresentIntroduced Invasive Julien & Griffiths, 1988; Krauss, 1963; Holm et al., 1979; EPPO, 2014

Central America and Caribbean

Trinidad and TobagoRestricted distributionEPPO, 2014

Oceania

AustraliaRestricted distributionIntroduced Invasive Holm et al., 1979; EPPO, 2014
-Australian Northern TerritoryPresent, few occurrencesIntroduced1983 Not invasive Fuller, 1993
-New South WalesWidespreadIntroduced1883 Invasive Rylands, 1966
-QueenslandWidespreadIntroduced1911 Invasive Gardner, 1930
-South AustraliaWidespreadIntroduced1870 Invasive Gardner, 1930
-TasmaniaEradicatedIntroduced Not invasive DPIWE, 2003
-VictoriaWidespreadIntroduced1883 Invasive Rylands, 1966
-Western AustraliaWidespreadIntroduced1830 Invasive Gardner, 1930
New ZealandRestricted distributionIntroducedHolm et al., 1979; Panetta and Mitchell, 1991; EPPO, 2014

History of Introduction and Spread

Top of page E. australis is a native of South Africa (Smith, 1966), initially restricted to the south-west and south-east regions, but has been spread inland by European settlers and farmers. The Portuguese are attributed with spreading the plant from South Africa to the 'Indes' (Steinheil, 1838). Steinheil (1838) also list E. australis as being found on Ascension Island, and Agnew (1974) stated that E. australis is a rare weed at medium altitudes in Kenya but that it had not been seen there for 15 years. It is uncertain whether E. australis still exists in either location. E. australis has been intercepted only, and is not present in the UK (Lousley and Kent, 1981).

In 1830, passengers travelling to Western Australia via South Africa thought that E. australis would be a useful vegetable to take to their new settlement so seeds were collected from Cape Town for cultivation along the banks of the Swan River (Western Australia). In Australia, the plant quickly became an unwanted weed, its spiny fruits spread by stock and rubber tyres. It was confined to Western Australia until 1870 before appearing in South Australia and then shortly afterwards in Victoria, New South Wales and southern Queensland (Gardner, 1930; Gilbey, 1974a). Isozyme studies (Panetta, 1990a) found two genotypes of E. australis within the Australian populations, but only one of these occurs in Western Australia. Western Australia could not therefore have been the source of genetic material for all populations present in Australia. Both genotypes exist across South Africa. Kloot (1987) blames fodder imported from South Africa rather than seed from Western Australia as the initial source of E. australis found in South Australia.

In New Zealand, E. australis has been present since 1883 and is widespread but not common on North Island and, whereas Panetta and Mitchell (1991) predict that the climatic conditions should be ideal for E. australis in many areas, the plant remains uncommon there. The stability of the plant communities resulting from perennial pastures and lack of crop/pasture rotations are believed to be the reason for E. australis not becoming weedy in New Zealand (Panetta and Mitchell, 1991). In Hawaii, introduced E. australis is a weed of pasture land (Krauss, 1963) having spread alarmingly quickly with Emex (both species collectively referred to) affecting 11,700 ha on Hawaii, Maui, Molokai and Oahu by 1962 (Goeden, 1978). However, introductions of a biological control agent (Perapion antiquum) have given substantial to complete control at altitudes of 600-1200 m although had no impact below 150 m (Julien and Griffiths, 1998).

Risk of Introduction

Top of page There is a high risk of accidental introduction of E. australis seeds and/or achenes as a contaminant of agricultural produce or attached to livestock or machinery. E. australis is considered noxious or declared (requiring control or eradication) in at least parts of every state in Australia and is noxious and prohibited (not to be introduced and must be eradicated if found) in Tasmania (Parsons and Cuthbertson, 1992). It is also declared a noxious weed in Japan (Kurokawa, 2001) and New Zealand (MAF, 2003). It is a Federal Noxious Weed in the United States as well as a noxious weed in Florida and North Carolina (USDA-NRCS, 2002).

Habitat

Top of page E. australis is adapted to grow on a wide range of soil types from loamy sands to clay loams, usually neutral to slightly alkaline and it can tolerate temperate to subtropical climates (Gilbey and Weiss, 1980). It thrives in open, disturbed and nutrient-enriched environments (Gilbey and Weiss, 1980) so it is predominantly a weed of agriculture. It is a relatively weak competitor, being out-competed by grasses and legumes (Panetta and Randall, 1993a), but it can dominate in habitats where environmental conditions such as drought or unseasonal rains can modify pasture composition (Gilbey, 1974a; Lemerle, 1996). In natural ecosystems it is typically restricted to areas disturbed by wind or water such as water holes, granite rocks, edges of creeks and alluvial flats (Keighery, 1996) or areas disturbed by the native fauna, for example by sea birds on the Abrolhos Islands of Western Australia (Keighery, 1996) or by Cape dune mole rats in Western Cape Province, South Africa (Scott, 1990).

Habitat List

Top of page
CategorySub-CategoryHabitatPresenceStatus
Terrestrial
Terrestrial – ManagedCultivated / agricultural land Present, no further details Harmful (pest or invasive)
Managed forests, plantations and orchards Present, no further details Harmful (pest or invasive)
Managed grasslands (grazing systems) Present, no further details Harmful (pest or invasive)
Disturbed areas Present, no further details
Rail / roadsides Present, no further details Harmful (pest or invasive)
Urban / peri-urban areas Present, no further details Harmful (pest or invasive)
Terrestrial ‑ Natural / Semi-naturalNatural forests Present, no further details
Natural grasslands Present, no further details Harmful (pest or invasive)
Riverbanks Present, no further details
Deserts Present, no further details
Littoral
Coastal areas Present, no further details Harmful (pest or invasive)

Hosts/Species Affected

Top of page Holm et al. (1979) found E. australis to be a serious weed in only two countries, Australia and South Africa. In South Africa, Cairns et al. (1979) recorded E. australis as one of the three most important weeds of wheat and the most important weed of medic pasture in the western Cape region of South Africa. It is also recorded as a weed of lucerne in South Africa (De Wit et al., 1962). In Australia, E. australis is a major weed of annual crops and pastures in grain-growing regions of southern Australia and in particular the south west of Western Australia (Gilbey and Weiss, 1980; Parsons and Cuthbertson, 1992). In 1974, over 1 million ha of pasture and 500,000 ha of cereal crops were affected in Western Australia alone (Gilbey, 1974a). It can be a major weed in crops either because of significant impacts resulting from direct competition between species (Hawkins and Black, 1958; Pearce, 1969; Gilbey, 1974b), difficulties in controlling it (Panetta and Randall, 1993b, Zaicou-Kunesch, 1996) or because of stringent near-zero tolerances on the level of contamination that is acceptable within produce (Bowran, 1996; Fromm, 1996; Pohlner, 1996). Being a weed of disturbed environments, it can potentially affect many crops with varying levels of impact. Parsons (1992) summarizes the herbicide products available in Australia at that time and notes the crops that each product is registered to be used within and the weeds that they are registered to target. Crops included in the 'Plants affected' table are crops listed in Parsons (1992) where a herbicide had been specifically registered for use against E. australis.

Growth Stages

Top of page Post-harvest, Pre-emergence, Seedling stage, Vegetative growing stage

Biology and Ecology

Top of page Genetics

The chromosome number of E. australis (based upon Australian populations) is 2n=20 (Putievsky et al., 1980) and is the same as both Australian and Portuguese populations of E. spinosa (Putievsky et al., 1980; Queiros, 1983). In Australia, where both species co-exist, the plants readily hybridise. Both species are monoecious with flowers of both sexes forming near the apex of the stems as the plant grows. Due to the more erect morphology of E. spinosa and as pollen is more likely to fall down than go upwards, seeds collected from E. australis plants were commonly outcrossed with E. spinosa but seeds collected from E. spinosa plants were only rarely outcrossed with E. australis (Putievsky et al., 1980). Putievsky et al. (1980) found the hybrids grew more vigorously than either parent, but were completely sterile when self-pollinated. They were, however, able to backcross with the parental species giving the possibility of gene flow between the species. There is very little genetic variability within E. australis (Weiss and Simmons, 1979; Panetta, 1990a). Panetta (1990a) states "E. australis provides an example of a sexually reproducing species whose patterns of within and between population variation are generally similar in both source and colonial regions. Indeed, 16 of the 21 surveyed South African populations could not be distinguished from Australian populations."

Physiology and Phenology

In areas with a Mediterranean climate, the emergence of E. australis usually begins in autumn after sufficient rain or in years with earlier rainfall, multiple waves of germination are often observed, each associated with significant rainfall events. Weiss (1981) found that up to six distinct cohorts may sometimes occur within a single year and attributed these to the earlier rains arriving before the majority of viable seed had completed their required period of innate dormancy. Although mid-season accessions may contain the most individuals, it was the first accessions of each year that contributed the most to seed production. Flowers could be produced within 4 weeks of germination and seeds within 6 weeks; however, this was highly variable and in some years it took 18 weeks before flowers were even produced. Seeds are produced continuously at the growing apex of the stems throughout the growing season. Regardless of when they germinate, all Emex plants die at the end of the winter rains when soil moisture disappears (Weiss, 1981). The longevity of the growing season can vary immensely from site to site and from year to year with 20-32 weeks after the first accession, reported in Weiss (1981). Within a Mediterranean climatic region, irrigation during the summer will permit some E. australis seeds to germinate and these can successfully complete development (Panetta, 1990b) but germination rates are lower than normal due to a proportion of the seed being dormant. Seedling densities can be over 900 plants/m² (Gilbey and Weiss, 1980), though more commonly 20-500 plants/m² in areas where E. australis is a problem (Gilbey and Lightfoot, 1979; Weiss, 1981; Scott, 1990; Panetta and Randall, 1993b; Scott and Shivas, 1998; Yeoh et al., 2002). At seedling densities of approximately 200 plants/m², survival from emergence to seed production is 40-50% in both Australia and South Africa (Scott, 1990).

In sub-tropical climates (e.g. KwaZulu-Natal and Eastern Cape provinces, South Africa), E. australis can grow all year round, germinating at any time but remaining an annual (Scott and Way, 1990). E. australis has three distinct phases of growth rate (Gilbey and Weiss, 1980). Under glasshouse conditions, for the first 8 weeks after emergence, growth rates are rapid and most energy is diverted towards foliage production. At 8-15 weeks there is a slight decrease in growth with foliage production decreasing but with more stem elongation, branching and buds, flower and fruit formation and a corresponding increase in root biomass. From 15 weeks senescence occurs and whilst during this phase there is no net increase in plant weight, resources from the leaves, stems and roots are reabsorbed and translocated to the developing achene. Embryo development begins in the seed 3 weeks after flowering and seeds are mature 6 weeks after flowering. Gilbey and Weiss (1980) report the average weight of achenes as being 20 mg, 50 mg and 60 mg at 3, 6 and 8 weeks respectively after flowering. The weight of the achene remained stable after it was 8 weeks old. Weiss and Simmons (1977) found that the optimum temperature for production of seed, stems and leaves was 11.7°C and for roots 16.7°C. A delayed flowering and necrosis of stems was shown at the lowest (6.7°C) and highest (26.7°C) temperatures tested. Above 16.7°C, there were only a few fertile seeds produced with no seeds fully maturing within 15 weeks at 26.7°C. A very strong positive correlation exists between temperature and rate of development until the temperature reaches approximately 19°C, becoming a negative correlation above this.

Within an annual pasture system of a Mediterranean climatic region, early cohorts of E. australis seedlings can result in response to significant summer rainfall events. This is due to the ability for some E. australis seed to germinate in response to moisture, relatively independently of temperature requirements (Weiss and Simmons, 1977; Panetta and Randall, 1993c). In Australia, these result from events such as cyclonic activity which happens reasonably frequently within northern New South Wales and northern Western Australia. Out of season rainfall events are locally referred to as a "false break". Follow up rains may not occur until several months latter when the true autumn/winter rains begin. The long tap root of E. australis seedlings allows them to survive the long dry period following a false break far better than most other annual species and in years where significant E. australis individuals survive a false break they can dominate the pastures and produce massive seed banks if left uncontrolled (Gilbey, 1974a; Weiss, 1981). This can lead to dramatic increases in infestations of E. australis in the following year (Lemerle, 1996).

Reproductive Biology

E. australis only reproduces by seed, is monoecious and self-compatible (Gardner, 1930). The spiny female flowers are sessile and in axillary clusters which form first on the crown, in the centre of the rosette, but subsequently in leaf axil nodes along the stems. The male flowers form in short axillary racemes, often emerging between the female achenes (Gilbey and Weiss, 1980). Stem growth, flower and subsequent seed production is continuous throughout the plant's lifetime. E. australis has a high degree of phenotypic plasticity with the extent of stem and node formation dependent upon environmental conditions and seed production being correlated with this stem and node production. Individuals growing under poor conditions (or in a short growing season) produce only a few seeds <10), but plants are capable of producing over 1100 seeds given favourable conditions (Weiss, 1978). E. australis invests a large proportion of its available resources into reproduction with highly stressed plants devoting 36%, and plants under more favourable conditions devoting 62% of all resources into achene and seed production (Weiss, 1978). Achene weight is variable from <10 mg to >90mg; however, Weiss (1978) found for Australian populations of E. australis the modal achene weight was 40-50 mg at the end of the growing season regardless of the plants' growing conditions. Weiss and Julien (1975) report mean achene lengths (capsule base to the top of the inner lobes of the female perianth) of 8.0 mm and mean widths (between two spine tips) of 9.5 mm. Massive seed banks can occur with up to 10,000 seeds/m² following the first year in pasture within a crop/pasture rotation, but over 17,000 seeds/m² is possible if E. australis plants are specifically protected from interspecific competition, pathogen and insect attack (Scott et al., 2000).

The persistence of E. australis and its ability to survive control measures is due to seed dormancy and longevity (Cheam, 1996). All seeds are dormant when freshly formed and require a 2-6 month period of after-ripening before they can germinate (Hagon and Simmons, 1978; Panetta and Randall, 1993c). Panetta and Randall (1993c), studying four populations of E. australis in Western Australian, found that if given the correct environmental conditions, most seeds (80-95%) were able to germinate at some stage during the following autumn. Whilst some seeds within the seed bank remained in this constant non-dormant state, the dormancy pattern in the majority (60-90%) followed the climatic patterns with germination being possible each winter but not possible each summer. A proportion of the seeds (5-20%) remained in a state of constant innate dormancy for the duration of the study (2 years). Seeds that remain in the constant non-dormant state give the species the flexibility to recruit opportunistically after summer rainfall events within the Mediterranean climate (Panetta and Randall, 1993c). Seeds that remain in the extended innate-dormant state ensure the continued recruitment of seedlings each year (Scott, 1990).

Despite most of the viable E. australis seeds being able to germinate each autumn, the proportion of seeds that actually germinates each season is usually low with only 15% of viable seeds reported germinating by Scott (1990) for E. australis in South Africa and 17% reported by Cheam (1996), 17.6% by Panetta and Randall (1993b), and 37% by Weiss (1981) for E. australis in Australia. Cultivation is known to increase germination (Gilbey and Weiss, 1980; Weiss, 1990). Another important factor is the ability of the seed to imbibe sufficient water for germination via its encapsulating, large, hard and spiny perianth (Cheam, 1987). As a consequence, unburied seeds have in general a low rate of germination. It would also explain Gilbey and Weiss's (1980) observation of lower emergence rates on sandy soils compared to heavier soils, which would retain higher moisture levels. Within a particular season, seeds buried 1-5 cm deep are most likely to become established (Scott, 1990; Cheam, 1996) whereas those on the soil surface or buried deeper than 10 cm are more likely to remain viable in future years thus acting as seed reservoirs in the event of future soil disturbances. Cheam (1996) studied germination patterns from E. australis seeds sown at 1-15 cm and over 4 years, there was 53.9% germination (79% of these within the first year) from seeds buried at 1 cm compared to 23.5% from seeds on the surface and 0% from seeds buried at 15cm. After 4 years, 21.0%, 10.5% and 18.3% of the initial seeds remained viable at 0, 1 and 15 cm depth, respectively. Some E. australis seeds can remain viable in the soil for more than 8 years (Gilbey, 1996).

Environmental Requirements

A prerequisite to invading a new habitat is the ability to tolerate the new climatic conditions. Values estimated within the Climate table are derived from long-term climatic averages from sites known to be at the edge of the known distribution range for E. australis in the native range in South Africa (Schulze, 1986) and where introduced in Australia (Plumb, 1977). Models for predicting the potential distribution of both species, based upon both climate and plant development requirements, are given in Pheloung et al. (1996). For E. australis in Australia, the predicted range is approximately identical to the current range and this the plant is not expected to spread much further. A similar model based on climatic conditions for New Zealand (Panetta and Mitchell, 1991) predicts a range that is considerably larger than the actual range even following over 100 years of opportunity.

Associations

E. australis is a good host of the root lesion nematode, Pratylenchus neglectus, a pest of certain varieties of cereal crops. It can be managed by the inclusion of non-host species grown in rotation with the susceptible crops therefore the presence of E. australis in the pasture phase of the rotation will hinder any implemented nematode-management practices (Vanstone and Russ, 2001). There is no known mycorrhiza associated with E. australis (Gilbey and Weiss, 1980). In Australia, both within pastures and crops, E. australis it is usually associated with other plant species in the families Compositae (in particular Arctotheca calendula), Cruciferae, Geraniaceae (in particular Erodium spp.), Gramineae, Leguminosae (in particular Trifolium spp.) or Polygonaceae (Gilbey and Weiss, 1980).

Seed of E. australis is an important component of the diet for small mammals. In Australia, up to a quarter of the seeds on the soil surface are removed by mice (Weiss, 1981) and in South Africa, a third are removed by gerbils (Scott, 1990). In the northern grain-growing region of south-west Australia, the seeds of E. australis are a major part of the diet of the Major Mitchell and inland red-tailed black cockatoos, but the amount of seed removed is insignificant (Scott et al. 2000) and the seeds are a minor food source for galahs, little and long billed corellas (Keighery, 1996).

Air Temperature

Top of page
Parameter Lower limit Upper limit
Mean annual temperature (ºC) 15 24
Mean maximum temperature of hottest month (ºC) 24 36

Rainfall

Top of page
ParameterLower limitUpper limitDescription
Dry season duration12number of consecutive months with <40 mm rainfall

Rainfall Regime

Top of page Bimodal
Summer
Winter

Soil Tolerances

Top of page

Soil drainage

  • free

Soil reaction

  • acid
  • alkaline
  • neutral

Soil texture

  • heavy
  • light
  • medium

Natural enemies

Top of page
Natural enemyTypeLife stagesSpecificityReferencesBiological control inBiological control on
Apion antiquum Herbivore Leaves/Stems
Brachycaudus rumexicolens Herbivore Leaves/Stems
Cercospora tripolitana Pathogen Leaves
Elegia inconspicuella Herbivore Leaves/Stems
Lophyrotoma analis Herbivore Leaves
Phomopsis emicis Pathogen Leaves/Stems
Rhinoncus australis Herbivore Leaves/Stems
Rhodometra sacraria Herbivore Leaves
Rhytirrhinus inaequalis Herbivore Roots
Uromyces rumicis Pathogen Leaves/Stems

Notes on Natural Enemies

Top of page The insects and pathogens associated with E. australis in the native range South Africa are listed in Scott and Way (1990), Shivas and Sivasithamparam (1994) and Shivas (1995). In the introduced range, the aphid Brachycaudus rumexicolens, itself an introduced species, is the most important herbivore in Australia, causing significant reduction in seed production (Scott and Shivas, 1998; Scott and Yeoh, 1998; 1999). The Australian native weevil, Rhinoncus australis also attacks plants, but does not develop populations sufficiently large to cause significant damage (Julien and Matthews, 1980). The Australian sawfly Lophyrotoma analis is commonly seen feeding on E. australis in Australia and can cause severe defoliation at some locations and in some years (Gilbey and Weiss, 1980). In Hawaii, Perapion antiquum has been used to successfully control this weed (Julien and Giffiths, 1998) and other species studied for their potential use as biological control agents are detailed in the Control section.

Means of Movement and Dispersal

Top of page Natural Dispersal (Non-Biotic)

Emex achenes float in water. Water is an important mode of dispersal and new infestations are likely to originate along culverts, fence lines, contour banks or any place where water can be trapped and deposit the seeds (Gilbey, 1975). E. australis achenes are large and heavy and so are unlikely to be dispersed by wind.

Vector Transmission (Biotic)

E. australis has hard thorny achenes that lie on the ground so that one thorn is always pointing upwards. Livestock pick up the achene on their feet and move them short distances, although the achene's spines will eventually cause lameness, thereby limiting the distances seed are dispersed by this method (Gilbey, 1975; Gilbey and Lightfoot, 1979).

Accidental Introduction

Attachment of the achenes to the tyres of vehicles, aircraft and machinery is the main method of spread, and allow the seeds to be transported long distances (Gilbey, 1975). Many farmers in Western Australia prevent the spread of the weed by picking out the seeds (by hand) from their tyres at paddock gates. Hay and grain purchased from infested farms can also be an important means of introduction (Gilbey, 1975; Lemerle, 1996) with hay fodder being more likely to contain E. australis seed than grain fodder in a study conducted within drought stricken areas of New South Wales, Australia (Thomas et al., 1984). Seeds of Emex are however sometimes found in feed wheat (grain) imported to Tasmania from mainland Australia (Parsons and Cuthbertson, 1992; DPIWE, 2003).

Intentional introduction

It is no longer regarded as a vegetable and has only limited beneficial characteristics (Gilbey and Weiss, 1980). It is not likely to be intentionally introduced anywhere.

Pathway Vectors

Top of page
VectorNotesLong DistanceLocalReferences
Clothing, footwear and possessionsSoles of shoes Yes
Containers and packaging - woodVineyear crates Yes
Land vehiclesCar rubber tyres Yes
Plants or parts of plantsGrain, fodder, fruit Yes
Soil, sand and gravel Yes

Plant Trade

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

Impact Summary

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

Impact

Top of page Although being a comparatively poor competitor against other weeds, E. australis can significantly impact upon crops. Within crops, E. australis seedlings compete for nitrogen at the beginning of the season and the mature plants compete for water at the end of the season. Hawkins and Black (1958) found E. australis (final densities of 10 plants/m²) reduced grain yields by 43% (Emex-free control plots yielding 2.4 t/ha) when no nitrogen was applied but only 34% (Emex-free controls yielding 3.2 t/ha) when nitrogen was added. A model by Black and Dyson (1993) predicts yield benefits of 122 kg/ha or 6% if E. australis infestations of 33 plants/m² are controlled at the 1-4 leaf stages. After controlling E. australis, increased wheat yields of 33% were reported by both Pearce (1969) who sprayed the plants (initially a 'heavy infestation') whilst at the 2 leaf stage to achieve gains of 670 kg/ha in grain yield, and Dellow et al. (1984) who sprayed the plants (initially at 50 plants/m²) at the 4-6 leaf stage to increase yields by 870 kg/ha. Gilbey (1974b) found plots with 30 or 90 Emex plants/m² had 25% and 50% lower yields, respectively, than their adjacent Emex-free control plots. In Western Australia, selective E. australis control increased lupin grain yields by 400-800kg/ha with competition from Emex plants estimated to cost that industry alone A$18M/year (Gilbey, 1995).

Economic impacts also occur post harvest. In Australia, the grain industry (cereals, pulses and oilseeds) has restrictions on levels of contamination with Emex seed, ranging from 0 (zero) Emex seed/500mls of malt barley in South Australia to 20 Emex seed/500ml of feed barley or lupins in Western Australia. For wheat, 8 Emex seed/500ml is the national maximum standard (Bowran, 1996). However, very few loads are declined due to Emex contamination (Fromm, 1996) as the comparatively large size of the E. australis seed facilitates its screening from the smaller sized grains (Weiss and Simmons, 1977). This, however, comes at a cost of A$12-$18 per tonne (Zaicou-Kunesch, 1996) or approximately 10% of the farm gate price that the farmer is likely to receive (Clark and Finlay, 1997). In the dried vine fruit industry, E. australis achenes attach to the bottom of plastic buckets and crates used during the picking and drying process. If dislodged, they contaminate the produce being difficult to remove because of their similar mass, size and colour. As the produce is used in breakfast cereals and other similar goods, there is an almost zero tolerance level (Pohlner, 1996). In 1993, the Australian penalty for having even one seed in a load was $173/tonne (Fletcher, 1993). Panagiotopoulos et al. (1987) summarises the tolerance for spiny fruits in this industry with his opening sentence "Dried fruit contaminated with caltrop, innocent weed or three corner jack (=E. australis) is of no commercial value."

As a weed of pastures, E. australis competes with beneficial pasture species and the sharp achenes can cause lameness of stock or introduce infection. In one example, 300 sheep from a flock size of 1800 contracted blackleg (Clostridium chauvoei) picked up through wounds inflicted whilst feeding on Emex plants, and was fatal for 60 of these (Rylands, 1966). In grazed pastures, reducing E. australis seedling densities from 150 plants/m to 30 plants/m resulted in a doubling of the available pasture for ewes and lambs, resulted in 73% heavier ewes, 21% higher values on lamb carcase value and 8% higher fleece value. The marked benefits gained from chemical control of E. australis in Australian pastures in 1979 (Gilbey and Lightfoot, 1979) disappeared during the 1980s and 1990s as meat and wool prices fell and chemical costs increased. Moderate direct short-term profits may still be made by using integrated control methods such as spray grazing (Peirce, 1993) but not always (Panetta and Randall, 1993b). Although Emex control within pasture may not result in immediate profits, it is important in the long term to reduce the seed bank (Peirce, 1993) allowing the legume component of the pasture to enrich soil nitrogen within a pasture/crop rotation farming system (Gilmour, 1996). Gilmour (1996) found controlling E. australis in the pasture phase of the rotation had benefits for the succeeding cereal phase, with a 16% (344 kg/ha) increase in wheat yield and a significant increase in the protein level of the grain (from 9.3% to 10.0%) resulting from the treatment.

Environmental Impact

Top of page In Hawaii, uncontrolled Emex forms dense mats of vegetation that shade out and displace useful plants, drying out during early summer leaving hillsides devoid of living vegetation and subject to sheet erosion (Goeden, 1978).

Impact: Biodiversity

Top of page In Western Australia, the inland red tailed black cockatoo (Calyptorhynchus banksii samueli Mathews), a protected native bird, extended its distributional range with the advent of farming activities introduced with European settlement. Previously, what is now a major grain-growing region was devoid of adequate water sources for the bird. The exotic E. australis seed is very abundant within this region and has a similar morphology to the bird's native food source. It is now the primary source of food of the bird within this artificially extended range and the release of a biological control agent in Australia targeting Emex was initially delayed as it was perceived as a threat to the bird's population within this grain-growing region. It was, however, allowed to proceed when studies showed that currently 50 times more seed is available than the cockatoo needed (Scott et al., 2000). In the grain-growing areas of Australia, E. australis is also a lesser food source for other native birds such as the Major Mitchell cockatoo, galahs and little and long billed corellas (Keighery, 1996; Scott et al., 2000). In South Africa E. australis is said to be an especially valuable feed for ostrich (Watt and Breyer-Brandwijk, 1962) and gerbils (Scott, 1990). In Australia, the natural areas that are likely to be invaded by E. australis (granite rocks, edges of creeks, riverline flats and alluvial flats) are also the areas likely to be centres of biological diversity and refugia. E. australis is therefore a threat to flora in these habitats (Keighery, 1996). occurs in many national parks within Australia but is not regarded as a major environmental weed.

Social Impact

Top of page Emex is of concern if it occurs in amenity areas such as sporting fields and parklands as the spiny achenes are sharp enough and strong enough to draw blood if trodden upon without shoes, and can even puncture thin walled rubber tyres of wheel barrows and bicycles. In most reserves and parks, however, regular cultivation or soil disturbance does not occur and Emex is not usually present (Fromm, 1996). Dogs, used to round up sheep, may refuse to work in Emex-infested paddocks and in some Australian areas leather boots are used to protect their feet (Rylands, 1966).

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
  • Damaged ecosystem services
  • Ecosystem change/ habitat alteration
  • Negatively impacts agriculture
  • Negatively impacts human health
  • Negatively impacts animal health
  • Negatively impacts tourism
  • Reduced amenity values
  • Reduced native biodiversity
Impact mechanisms
  • Competition - monopolizing resources
  • Pest and disease transmission
  • Produces spines, thorns or burrs
Likelihood of entry/control
  • Highly likely to be transported internationally accidentally
  • Difficult/costly to control

Uses

Top of page The leaf has previously been used as spinach but it is no longer regarded as a vegetable (Gilbey and Weiss, 1980). Early settlers in the Cape of South Africa used young E. australis leaves as spinach which made a "tolerably good, although slightly aperient, dish" (Shivas and Sivasithamparam, 1994). Watt and Breyer-Brandwijk (1962) report that in South Africa the plant is eaten by livestock before the achenes have formed and that it is a valuable food source for ostriches. Emex australis is palatable to stock and is readily grazed, especially prior to the formation of the spiny achenes (Panetta and Randall, 1993a). Royce (1963) however warns against overgrazing stock on E. australis as the leaves contain high levels of oxalic acid and this has resulted in the death of several stud rams that were feeding on E. australis seedlings. E. australis is reported to have medicinal value, used by Zulu as a remedy for stomach disorders and colic and they are used by the Xhosa to relieve dyspepsia and biliousness and to stimulate appetite. The Xhosa are also quoted as using it to control threadworm in horses.

Similarities to Other Species/Conditions

Top of page Within the Polygonaceae family (identifiable by the ochreae), only plants within the genus Emex have single-seeded, woody fruiting bodies (achene) with the three thorny spines arranged at 120° to each other so that one always faces upwards when the seed is on the ground. E. spinosa and E. australis are the only species within the genus. Grown under identical conditions E. australis is more prostrate (average 56 cm versus 80 cm tall), has fewer seeds per rosette (average 4.7 versus 8.8), per node (average 2.2 versus 6.2) and per plant (average 346 versus 987) and the achenes are longer (average 8 mm versus 5.5 mm) and wider (average 9.5 mm versus 5.2 mm) than E. spinosa (Weiss and Julien, 1975). All these characteristics are, however, highly dependent upon environmental conditions (Weiss and Simmons, 1979). Gilbey (1974a) and Gilbey and Weiss (1980) differentiated the species based upon the young seedlings and the shape of achenes. Cotyledons are linear in E. spinosa but narrowly elliptic and taper at both ends in E. australis. The apex of the first true leaf (but not necessarily later leaves) is acute in E. spinosa but obtuse in E. australis. When viewed from the side with the pedicle pointing towards the ground, the mature aerial achene in E. spinosa has spines that are short and slender and pointing horizontally or downwards and the lower half of the seed capsule is truncated so the widest part is near the pedicle (Gilbey and Weiss, 1980). Siddiqi (1973) reports that on each of the three flat faces (between spines) are six small pits, although the actual number of small pits can vary with 8-10 pits per face (Parsons and Cuthbertson, 1992). In E. australis, the aerial achene when viewed in the same way has spines that are long and robust and point slightly upwards. The lower half of the seed capsule is rounded with the widest part being just below the spines (Gilbey and Weiss, 1980). On each of the three flat faces are four pits (Siddiqi, 1973). In areas where E. australis and E. spinosa coexist, hybrids can form and they resemble the form of E. spinosa (Putievsky et al., 1980).

Prevention and Control

Top of page Cutlural control

The success of E. australis in Australia has been attributed to the traditional use of a crop/pasture rotational farming system and, "Doublegee would probably become insignificant (in Australia) under continuous cropping or in permanent pasture" (Dodd and Panetta, 1993). Panetta and Mitchell (1991) considered that the lack of significant invasion of E. australis in New Zealand was due to the absence of rotational farming systems or other regular forms of soil disturbance and that E. australis is unable to successfully invade the stable perennial-pasture communities. Thus a change in land use or affected land management may be expected to have a significant effect on the spread of E. australis. In Australia, the country where E. australis has become most weedy, grain farmers have traditionally used cereal-legume rotational cropping systems so as to break crop disease cycles and to add nutrients to the soil. Prior to the 1980s, the rotational system typically incorporated legume based annual pastures that were grazed by sheep (Powles and Bowran, 2000). The chemical control of Emex within this pasture phase was difficult because reliable and selective herbicides were not available (Panetta and Randall, 1993b) and grazing was the main management tool to maintain pasture balance and prevent weed dominance (Peirce, 1993). E. australis has a relatively low competitiveness (Panetta and Randall, 1993a) that is exploited in vineyards by planting dense cover crops (cereals or legumes at twice their normal rates) between rows so as to minimize achene production from Emex plants that survive applications of pre-emergent herbicides. Cover crops are then slashed at the end of winter to form a mulch that not only suppresses further weed growth but also aids in retaining soil moisture (Code, 1990; Lang, 1990; MacGregor, 1990). Panetta and Randall (1993a) propose managing Emex by tolerating preferential weeds or by periodically resowing pasture legumes, a method which also proved successful in Hawaii prior to the development of biological control.

Mechanical Control

With small infestations, individual plants can be grubbed out and destroyed. Gardner (1930) reports good results being obtained by using a hoe to sever the taproot just below the crown, before seeds have formed. In broad acre farming, a shallow cultivation before germination encourages a quicker and thicker germination of Emex seedlings that can then be killed by a follow-up cultivation or by herbicides (Pearce, 1973). Several cultivations are effective in controlling most weeds, including Emex, but this can reduce the potential growing season of the crop by over 4 weeks reducing crop yield, and it is unsustainable in areas with light, fragile soils as cultivation promotes wind and water erosion (Powles and Bowran, 2000). In vineyards, undervine cultivation is useful in removing larger, hard-to-kill plants prior to herbicide usage. Carpet-covered 'prickle rollers' are used to manually collect and remove achenes from fruit drying areas and vehicle movement is restricted to reduce spreading the achenes.

Chemical Control

As E. australis seeds can remain viable in the seed bank for over 8 years, chemical control will only affect those plants that have germinated in the current season and control measures must be repeated annually for many years to completely deplete the seed bank. The timing of the application of herbicides is critical for the control of E. australis, with post-emergence herbicides applied before the plants are at the 4-5 leaf stage when control becomes less reliable. Once runners have formed, most herbicides applied at the label rate will be ineffective and plants at this stage will also have already set seed (Gilbey, 1990). Gilbey (1990) and Commens (1997) are useful references for the use and costs of herbicide control of Emex in cereals, lupins, peas, clover and vines in parts of Australia. Herbicide-resistant weeds are an increasing problem promoted by the heavily reliance on post-emergent herbicides and in particularly by the persistent usage of the same type of chemical. Weed management strategies should aim to minimize herbicide use (e.g. by incorporating cultural methods), avoid the consecutive use of herbicides that belong to the same herbicide group, and understand that certain herbicide groups (e.g. A and B) are more prone to resistance than others (Preston, 2003). Although there are no current records of herbicide-resistant Emex plants (Heap, 2003), other members of the same family have developed resistant biotypes.

Members of the Polygonaceae (including Emex) are highly susceptible to dicamba and in Australia this has been used extensively for E. australis control within cereals from the 1970s until the mid 1980s when the sulfonylurea herbicides were used. The sulfonylurea herbicides are cheaper, have a broader target spectrum and can cope with a wider range in plant size and density, but have longer plant-back periods (Addenbrooke, 1996; Ralph, 1996). E. australis control in medic pasture in Australia was achieved with diuron + 2,4-DB, and a herbicide containing imazethapyr, with the former influencing pasture composition resulting in more grasses (Panetta and Randall, 1993b). Gilbey (1995) also warns that even low rates of diuron + 2,4-DB can damage clover. More recently there has been an increase in the availability of herbicides such as those containing flumetsulam or bromoxynil + diflufenican (Commens, 1997), but which must be used with caution on legume-based pastures and crops because herbicide tolerance varies widely between legume species/cultivars (Revell and Rose, 2001). Field chemical trials on Emex control within medic and sub-clover pastures (Gilmour, 1996) gave 97.8% reduction in E. australis seed production with flumetsulam + diuron and 77.2% seed reduction with diuron + 2,4-DB and neither treatments had any detrimental effects on legume seed production.

After the 1980s, decreasing values of meat and wool, the availability of non-selective knock-down herbicides such as glyphosate and the tendency towards minimum tillage systems so as to minimise erosion has resulted in more Australian farmers selling their livestock and turning to continuous cropping with cereals being rotated with lupins, pulses or oil seed crops. In the absence of the standard cultural control methods such as cultivation and grazing, weed control in these systems becomes heavily or totally dependent upon chemicals (Powles and Bowran, 2000). Broadleaf weed control in the previous cereal crop and the application of a total knock-down chemical (e.g. glyphosate or bipyridylium) before planting are essential to reduce in-crop weed control in the non-cereal phase. Simazine in conjunction with cultivation gives good control of Emex in Lupins (Gilbey, 1995); diuron can be used for control of Emex in lupins, peas and Lucerne; methabenzthiazuron can be used in peas and imazethapyr can be used in faba beans and peas (Commens, 1997). In conventional canola, broadleaf weed control in general is difficult due to the lack of suitable herbicides (Zaicou-Kunesch, 1996). Non-genetically modified triazine-tolerant (TT) and imidizalinone-tolerant (IT) varieties of canola were released in Australia in the late 1990s (OTGR, 2002). Simazine or atrazine are used to control Emex within TT Canola. IT Canola is widely planted in Emex-dominated areas because imazapic and imazapyr provide good control of E. australis; however, the emergence of resistance in other weeds (e.g. ryegrass) can curtail this (OTGR, 2002).

In Australian horticultural crops, ioxynil and methabenzthiazuron are registered for controlling Emex in onions, metribuzin for control in potatoes and in many other vegetables, chlorthal dimethyl or prometryn are used (Parsons and Cuthbertson, 1992). In vineyards and orchards, general knock-down herbicides such as glyphosate are used under the vines/trees to successfully control small Emex plants. The herbicides diuron, simazine and amitrole + atrazine (Gilbey, 1990) and bromacil are used for controlling Emex in citrus (Parsons and Cuthbertson, 1992). Moore and Moore (2003) provide information on the currently registered herbicides for control of E. australis plants at their various stages of development, listing 43 different active ingredients that are registered in Australia for the control of E. australis.

Biological Control

The early success of biological control against E. australis in Hawaii has led to a continuing effort to implement this technique in Australia where this weed is a major problem. Perapion antiquum, a weevil from South Africa, was released on four islands in Hawaii providing substantial to complete control at elevations of 600-1200 m (Julien and Griffiths, 1998). Other weevils, Perapion neofallax and Perapion violaceum were also released but did not establish on Hawaii. Perapion antiquum was released extensively in Australia during the 1970s and 1980s. Establishment was recorded at three sites but no control was achieved, and climatic reasons were suggested as the reason for the different degrees of success in Hawaii and Australia (Scott, 1992). Lixus cribricollis, a weevil from E. spinosa in Morocco, was also released for the control of E. australis in 1979, but did not establish (Julien and Griffiths, 1998). Recently, Apion miniatum, a weevil collected from E. spinosa in Israel has been released extensively in Western Australia but establishment is not confirmed (Yeoh et al., 2002).

The search for potential biological control agents against this weed also includes studies of the biology and host range of indigenous insects and pathogens attacking this weed. Species studied include: Microthrix inconspicuella (Harley et al., 1979; Shepherd, 1990); Perapion antiquum (Harley and Kassulke, 1975); Rhodometra sacraria (Scott and Way, 1989b; Shepherd, 1989); and Rhytirrhinus inaequalis (Scott and Way, 1989a). Indigenous pathogens that have been studied include Cercospora tripolitana (Morris, 1984); Uromyces rumicis (Morris, 1982), which has also been reported from greenhouse plants in Australia (Shivas, 1987), but not established in the field (Scott and Shivas, 1993); and Phomopsis emicis, which was subsequently discovered established in Australia (Shivas et al., 1994) where it damages up to 30% of seed production (Shivas et al., 1994; Scott and Shivas, 1998).

Integrated Control

Emex is palatable to stock and is readily grazed until the formation of the spiny achenes. Defoliation delays stem and seed production as well as decreasing root growth (Weiss, 1976) which should result in the plant, which is by nature a poor competitor (Panetta and Randall, 1993a) becoming even less competitive. Goats preferentially graze on weeds over clovers but given a choice they prefer brassica weeds, annual rye or barley grass to Emex (Peirce, 1993). Indirect control of Emex can however be obtained by manipulating grazing pressures. The taller grasses are able to out-compete shorter broadleaf plants by shading them and therefore are favoured by no or light grazing. Emex and other similar early germinating broadleaved weeds are favoured by medium grazing; the highly competitive legumes such as subclover, which also produce more runners and below-ground seed in response to damage, are favoured by heavy grazing (Madin and Moore, 1993; Peirce, 1993). Excellent E. australis control in legume-based pastures can be obtained by integrating grazing with herbicides or the 'spray-graze' technique (Pearce, 1972). Sub-lethal low doses of herbicides such as 2,4-D, 2,4-DB or MCPA amine are used to induce wilting and elevated sugar levels in the Emex plants (and other broadleaved weeds). This increases their accessibility and palatability and under heavy grazing (four times the normal stocking rates) they are quickly either eaten out completely or at least made an unimportant species within the pasture. If grazing pressures are not high enough, stock may still avoid the Emex in preference for other broadleaved weeds and any plants not grazed within 2-3 weeks will fully recover from the sub-lethal dose of herbicide (Peirce, 1993). Although spray-grazing is the most common form of E. australis control in some regions, Panetta and Randall (1993b) state that it has not been widely adopted because of the significant effort and resources needed to obtain the required short-term elevated grazing pressures.

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