Invasive Species Compendium

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Datasheet

Emex spinosa
(spiny emex)

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Datasheet

Emex spinosa (spiny emex)

Summary

  • Last modified
  • 16 November 2018
  • Datasheet Type(s)
  • Invasive Species
  • Pest
  • Host Plant
  • Preferred Scientific Name
  • Emex spinosa
  • Preferred Common Name
  • spiny emex
  • Taxonomic Tree
  • Domain: Eukaryota
  •   Kingdom: Plantae
  •     Phylum: Spermatophyta
  •       Subphylum: Angiospermae
  •         Class: Dicotyledonae
  • Summary of Invasiveness
  • E. spinosa is a relatively weak competitor but has several strong colonizing characteristics including drought tolerance, rapid growth, abundant seed production, seed dormancy and high dispersal abilities and the two types of achene give the plant it...

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Pictures

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PictureTitleCaptionCopyright
(a) achenes from crown (subterranean ), (b) achenes from crown (above soil surface), (c) aerial achenes. Sequence from top to bottom of column:
1) mature, 2) immature sectioned, 3) immature, complete.
TitleAchenes
Caption(a) achenes from crown (subterranean ), (b) achenes from crown (above soil surface), (c) aerial achenes. Sequence from top to bottom of column: 1) mature, 2) immature sectioned, 3) immature, complete.
CopyrightPaul B. Yeoh/CSIRO
(a) achenes from crown (subterranean ), (b) achenes from crown (above soil surface), (c) aerial achenes. Sequence from top to bottom of column:
1) mature, 2) immature sectioned, 3) immature, complete.
Achenes(a) achenes from crown (subterranean ), (b) achenes from crown (above soil surface), (c) aerial achenes. Sequence from top to bottom of column: 1) mature, 2) immature sectioned, 3) immature, complete.Paul B. Yeoh/CSIRO
E. spinosa seedlings showing the long and narrow (linear) cotyledons and the first true leaf with its acute apex.
TitleSeedlings
CaptionE. spinosa seedlings showing the long and narrow (linear) cotyledons and the first true leaf with its acute apex.
CopyrightPaul B. Yeoh/CSIRO
E. spinosa seedlings showing the long and narrow (linear) cotyledons and the first true leaf with its acute apex.
SeedlingsE. spinosa seedlings showing the long and narrow (linear) cotyledons and the first true leaf with its acute apex.Paul B. Yeoh/CSIRO
A large E. spinosa rosette growing in sandy wasteland in Israel.
TitleHabit
CaptionA large E. spinosa rosette growing in sandy wasteland in Israel.
CopyrightJohn K. Scott/CSIRO
A large E. spinosa rosette growing in sandy wasteland in Israel.
HabitA large E. spinosa rosette growing in sandy wasteland in Israel.John K. Scott/CSIRO
A large, mature E. spinosa plant growing in a fallow field in Israel.
TitleHabit
CaptionA large, mature E. spinosa plant growing in a fallow field in Israel.
CopyrightJohn K. Scott/CSIRO
A large, mature E. spinosa plant growing in a fallow field in Israel.
HabitA large, mature E. spinosa plant growing in a fallow field in Israel.John K. Scott/CSIRO
Emex australis (a) and E. spinosa (b) both grown for 15 weeks under identical glasshouse conditions.
TitleSpecies comparison
CaptionEmex australis (a) and E. spinosa (b) both grown for 15 weeks under identical glasshouse conditions.
CopyrightPaul B. Yeoh/CSIRO
Emex australis (a) and E. spinosa (b) both grown for 15 weeks under identical glasshouse conditions.
Species comparisonEmex australis (a) and E. spinosa (b) both grown for 15 weeks under identical glasshouse conditions.Paul B. Yeoh/CSIRO
Emex australis (a) and E. spinosa (b) both grown under identical glasshouse conditions. Soil has been removed to show their root systems.
TitleSpecies comparison
CaptionEmex australis (a) and E. spinosa (b) both grown under identical glasshouse conditions. Soil has been removed to show their root systems.
CopyrightPaul B. Yeoh/CSIRO
Emex australis (a) and E. spinosa (b) both grown under identical glasshouse conditions. Soil has been removed to show their root systems.
Species comparisonEmex australis (a) and E. spinosa (b) both grown under identical glasshouse conditions. Soil has been removed to show their root systems.Paul B. Yeoh/CSIRO
E. spinosa aerial achenes and flowers.
TitleAerial achenes
CaptionE. spinosa aerial achenes and flowers.
CopyrightPaul B. Yeoh/CSIRO
E. spinosa aerial achenes and flowers.
Aerial achenesE. spinosa aerial achenes and flowers.Paul B. Yeoh/CSIRO
E. spinosa crown and taproot region with subterranean achenes.
TitleSubterranean achenes
CaptionE. spinosa crown and taproot region with subterranean achenes.
CopyrightPaul B. Yeoh/CSIRO
E. spinosa crown and taproot region with subterranean achenes.
Subterranean achenesE. spinosa crown and taproot region with subterranean achenes.Paul B. Yeoh/CSIRO

Identity

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Preferred Scientific Name

  • Emex spinosa (L.) Campd.

Preferred Common Name

  • spiny emex

Other Scientific Names

  • Emex spinosus
  • Rumex glaber Forsk.
  • Rumex spinosus L.
  • Vibo spinosa (L.) Medik.

International Common Names

  • English: devil's thorn; lesser jack; little jack; prickly dock; spiny three-corner jack
  • Spanish: romaza espinosa
  • French: emex épineux
  • Arabic: derrs al'agouz

Local Common Names

  • Egypt: dirs el-agooz
  • Germany: Dornige Emex
  • Iran: havij sahra'ee; torob koohee
  • Pakistan: kafir kanda

EPPO code

  • EMESP (Emex spinosa)

Summary of Invasiveness

Top of page E. spinosa is a relatively weak competitor but has several strong colonizing characteristics including drought tolerance, rapid growth, abundant seed production, seed dormancy and high dispersal abilities and the two types of achene give the plant its invasive properties. Rapidly produced large subterranean achenes maximise the progeny's fitness/competitiveness whilst numerous (>1000/plant) small spiny aerial achenes maximise the colonizing characteristics of the species. The seeds have the potential to remain viable for many years within the soil enabling the species to persist through long periods of unfavourable conditions. In order to restrict the plant's introduction or spread via human intervention, E. spinosa is declared noxious in several countries including Australia, USA, Japan, New Zealand and Morocco.

Taxonomic Tree

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

Notes on Taxonomy and Nomenclature

Top of page The type specimen for Emex spinosa (L.) Campdera (1819) was collected from Crete, Greece (Siddiqi, 1973). The genus name Emex is thought to be derived from Rumex, the genus in which it was originally placed, and the Latin word ex, 'out of' (Shivas and Sivasithamparam, 1994). Its species name, 'spinosa' is Latin for 'prickly or thorny' and presumably refers to its achenes. Zohary (1966) describes two varieties of E. spinosa, var. spinosa and var. minor.

Description

Top of page E. spinosa is an autumn-winter germinating annual that can only reproduce by seed. Cotyledons are hairless and linear and the first leaf is oval with an acute apex (Gilbey and Weiss, 1980), whereas 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 has stems that are round, ribbed and sometimes reddish. Stems are decumbent to erect (Zohary, 1966), radiating from the crown in all directions and branching dichotomously at periodic nodes. On the nodes of the stem, at the base of the petioles, are brown membranous ochreae (circa 5 mm long). The basal leaves are usually the longest, lamina up to 15 cm, and become smaller, down to 3 cm, moving along the stem and away from the crown.

The small (circa 2 mm), inconspicuous green flowers have predominantly separate sexes but are self-compatible and from these a hard wooden achene (fruit) with three spines (=modified lobes of the perianth) develops. The spiny female flowers are sessile and form in axillary clusters in the axils of the leaves forming first on the crown about a month after the seed has germinated and whilst the plant is still a rosette (Evenari et al., 1977). The male flowers, together with the occasional perfect flower, form in short axillary racemes, often emerging between the female achenes (Zohary, 1966). Each achene contains a single, trigonous seed. Achenes are dimorphic with large (36-75 mg) and not very spiny subterranean achenes formed, attached to the crown near the neck of the root and smaller (13.5-14.9 mg) aerial achenes with very sharp spines formed at the nodes of the above ground stem (Evenari et al., 1977; Weiss, 1980). The aerial achenes are triangular in cross section with their spines arranged so that one spine always points outwards. Immature achenes are originally green (aerial) or white/yellow and red (subterranean) but turn brown as they ripen. Achenes ripen in approximately the same order as conception so distal achenes will be still developing whilst proximal achenes on the same branch are ripe. Due to the continuous growing nature of the plant, the size of aerial achenes varies greatly within a single plant, with proximal achenes weighing 23.7 mg each and approximately 5 mm long but distal achenes weighing only 2.2 mg each and are only 1-2 mm long (Evenari et al., 1977).

Zohary (1966) describes two varieties of E. spinosa. E. spinosa var. spinosa is a plant with large leaves (to 12 cm), petioles shorter than the leaf blades, large achenes (6-8 mm) and club-shaped cotyledons that inhabits roadsides and fields, and E. spinosa var. minor is a plant with small leaves (less than 5 cm), petioles longer than the blade, small achenes (4-6 mm) and narrow, linear cotyledons that inhabits steppes and deserts. Weiss (1980) considers the Australian populations to be more similar to E. spinosa var. spinosa than to E. spinosa var. minor; however, the Australian plants have linear cotyledons (Gilbey, 1974; Gilbey and Weiss, 1980). Wilding et al. (1993) distinguish Australian populations of E. spinosa from E. australis by the relative length of the petioles whilst at the rosette stage, the petioles being longer than the leaf blades for E. spinosa but not for E. australis.

Plant Type

Top of page Annual
Broadleaved
Herbaceous
Seed propagated

Distribution

Top of page E. spinosa is native to islands of, and countries bordering the Mediterranean. Jalas and Suominen (1979) mapped the regions in southern Europe where E. spinosa has been recorded showing it to be widely distributed on the mainland along the coastal regions of Portugal, Spain, and Greece. It is also common on the islands within the Mediterranean Sea with records shown for the Balearic Islands, Sardinia, Corsica, Sicily, Malta and Crete. However, there is a noticeable absence of records on the mainland coast from France all the way east to Albania, the exception being a couple of records on the eastern coast of Italy (around Bari). In Jalas and Suominen (1979), the only depicted locations that are non-coastal are on the Tagus River, Spain, where it has been located several hundred kilometres inland. Kosinova (1974) found E. spinosa distribution was restricted to the cultivated lands in Egypt and was one of only a few Mediterranean weeds to penetrate to the southern Egyptian regions near Nubia.

Where introduced, E. spinosa is present in many countries and whilst it is a common weed in Kenya (Agnew, 1974) it has only ever become a serious weed in the Hawaiian Islands (Holm et al., 1979). Kosinova (1974) states that it has been found only once in Sudan, and has a very limited distribution in Australia (Gilbey 1974; Pheloung et al., 1996). Siddiqi (1973) reports E. spinosa as being a weed in north-west Pakistan but notes that it is not common, and it is reported as rare in India (Varma et al., 1984).

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

IndiaPresentPresent based on regional distribution.
-BiharPresent, few occurrencesIntroduced1984 Not invasive Varma et al., 1984
-RajasthanPresent, few occurrencesIntroduced Not invasive Varma et al., 1984
IranPresentIntroduced Not invasive Siddiqi, 1973
IraqPresentIntroduced Not invasive Siddiqi, 1973
IsraelRestricted distributionNativeZohary, 1966; Holm et al., 1979; Greuter et al., 1989; EPPO, 2014
JordanPresentNativeGreuter et al., 1989
LebanonPresentNativeGreuter et al., 1989
PakistanPresent, few occurrencesIntroduced Not invasive Siddiqi, 1973
Saudi ArabiaPresentIntroducedMissouri Botanical Garden, 2003
SyriaPresentNativeGreuter et al., 1989
TurkeyPresentNativeDavis, 1967; Greuter et al., 1989

Africa

AlgeriaPresentNativeGreuter et al., 1989
EgyptRestricted distributionNative Invasive Kosinova, 1974; Greuter et al., 1989; EPPO, 2014
KenyaRestricted distributionIntroducedGraham, 1958; Agnew, 1974; Holm et al., 1979; EPPO, 2014
LibyaPresentNativeGreuter et al., 1989
MauritiusRestricted distributionEPPO, 2014
MoroccoRestricted distributionNative Invasive Holm et al., 1979; Greuter et al., 1989; EPPO, 2014
Spain
-Canary IslandsPresentIntroducedbefore 1838Steinheil, 1838
TunisiaPresentNativeGreuter et al., 1989

North America

USAWidespreadIntroducedHolm et al., 1979; EPPO, 2014
-CaliforniaRestricted distributionIntroducedRobbins et al., 1970; USDA-NRCS, 2002
-FloridaRestricted distributionIntroducedUSDA-NRCS, 2002
-HawaiiPresentIntroduced Invasive Nakao, 1969; Holm et al., 1979; Julien and Griffiths, 1998; USDA-NRCS, 2002; EPPO, 2014
-MassachusettsRestricted distributionIntroducedUSDA-NRCS, 2002
-New JerseyRestricted distributionIntroducedUSDA-NRCS, 2002
-TexasRestricted distributionIntroducedUSDA-NRCS, 2002

South America

BrazilPresentIntroducedbefore 1838Steinheil, 1838
EcuadorPresentIntroducedBrandbyge, 1989; Missouri Botanical Garden, 2003

Europe

CyprusPresentNativebefore 1838Greuter et al., 1989
France
-CorsicaAbsent, formerly presentNativebefore 1838Jalas and Suominen, 1979
GibraltarPresentNativeLinares, 2001
GreeceWidespreadNativeTutin et al., 1964; Jalas and Suominen, 1979; Greuter et al., 1989
ItalyPresentNativeTutin et al., 1964; Jalas and Suominen, 1979; Greuter et al., 1989
MaltaPresentNativeJalas and Suominen, 1979
PortugalRestricted distributionNativeTutin et al., 1964; Holm et al., 1979; Jalas and Suominen, 1979; Greuter et al., 1989; EPPO, 2014
-AzoresPresentIntroducedTutin et al., 1964; Jalas and Suominen, 1979
SpainWidespreadNativeTutin et al., 1964; Jalas and Suominen, 1979; Greuter et al., 1989
-Balearic IslandsPresentNativeTutin et al., 1964; Jalas and Suominen, 1979; Greuter et al., 1989
UKAbsent, intercepted onlyIntroduced Not invasive Lousley and Kent, 1981

Oceania

AustraliaRestricted distributionIntroduced Invasive Holm et al., 1979; EPPO, 2014
-QueenslandRestricted distributionIntroduced1953 Not invasive Weiss and Simmons, 1979
-South AustraliaRestricted distributionIntroduced1974 Not invasive Gilbey, 1974
-VictoriaRestricted distributionIntroduced1974 Not invasive Weiss and Julien, 1975
-Western AustraliaRestricted distributionIntroducedCirca 1900? Confirmed 1938. Not invasive Gilbey, 1974

History of Introduction and Spread

Top of page In Australia, Gilbey (1974) states that it was first collected in 1953 from an inland pastoral town in Western Australia where the locals said it had been present since 1938. Its distribution occurs along the old stock routes that lead from the inland pastoral areas to what was previously the main port; it is thought to have been introduced with fodder for livestock around 1900 (Gilbey, 1974). Isozyme studies (Marshall and Weiss, 1982) suggest that there have been at least four separate and independent introductions of E. spinosa into Australia, with the populations in Queensland, Victoria and the Eyre Peninsula, South Australia, all arriving independently from abroad rather than being introduced from the original introductions in Western Australia.

The Portuguese are attributed with spreading the plant from Portugal to the Canary Islands and to Brazil (Steinheil, 1838). On the Hawaiian Islands, E. spinosa is thought to have been accidentally introduced with grass seed and became widespread, taking over large areas of pasture land (Nakao, 1966). By 1962, E. spinosa and E. australis affected 11,700 ha on Hawaii, Maui, Molokai and Oahu (Goeden, 1978). Fullaway (1958) states "the weed was taking over fairly large areas of pasture on the Parker Ranch, on the island of Hawaii, the largest ranch in the Territory and most efficiently managed" before measures were "initiated to suppress it". After suitable biological control agents were introduced to the Hawaiian Islands, Emex spp. lost their competitive edge and in most parts no longer need to be controlled with chemicals.

Under a range of typical growing conditions, E. spinosa was predicted to have a competitive advantage over E. australis due to the earlier development of flowers, runners and seeds and because of a larger seed output (Weiss and Simmons, 1977). Pot competition trials and a field study conducted in Victoria, Australia where both species were growing together confirmed this (Weiss, 1977; Weiss and Simmons, 1977). Both species have similar growing requirements and largely overlap in their predicted potential distribution (Pheloung et al., 1996) and it was expected that E. spinosa might out-compete and therefore replace E. australis in many parts of Australia (Weiss, 1977). Williams et al. (1984) confirmed that when grown together, E. spinosa was competitively superior to E. australis; however, these authors observed a reversal in the competitive hierarchy when another species (wheat) was introduced into the community. Furthermore, the authors found that at low soil nitrogen levels, both Emex spp. were less competitive than wheat but with high soil nitrogen levels, E. australis became more competitive whilst E. spinosa remained less competitive than wheat. E. australis rapidly became widespread and a serious weed within the grain-growing regions of Australia whereas E. spinosa has always been restricted to a few localized areas (Parsons and Cuthbertson, 1992; Pheloung et al., 1996). Other factors such as a potentially lower dispersal capacity of E. spinosa achenes (Gilbey, 1974) may reduce the rate of spread within Australia, but it would appear that the most likely factors restricting the spread are the poor competitive ability of E. spinosa together with the fact that E. australis already occupies most suitable habitats.

Risk of Introduction

Top of page There is a high risk of further accidental introduction of E. spinosa as a contaminant or affixed to vehicles. It is considered noxious or declared (requiring control or eradication) in parts of every state in Australia and is noxious and prohibited (not to be introduced and must be eradicated if found) in Tasmania (Bowran, 1996). 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). It is even considered noxious in Morocco (WANA, 2001) where it is native.

Habitat

Top of page E. spinosa can tolerate a range of habitats but is generally a plant of disturbed environments favoured by human activities such as farming, building of roads and railways and by natural disturbances such as drought and floods. In Mediterranean countries where it is native, distribution is restricted to coastal areas, islands and river banks (Kosinova, 1974; Jalas and Suominen, 1979). Within areas of agriculture, it generally grows on sandy places in fields, orchards and gardens (Bischof, 1978) being a weed of horticulture (Siwicki 1967; Koren and Arenstein, 1973; Lifshitz et al., 1987a,b; Rzozi, 1999) and broad acre crops (Ibrahim et al., 1988; Hadar et al., 1999). In other areas of human disturbance, it occurs along roadsides (Zohary, 1966) in spaces between buildings as well as being able to survive on top of old walls, steps and flat roofs and within highly polluted canals and olive groves (Brandes, 2001). A cemetery is noted as the main site for E. spinosa on Gibraltar (Linares, 2001). Naturally disturbed areas colonized by E. spinosa include coastal sand dunes (Brandes, 2001), steppes and deserts (Zohary, 1966). In the Negev highlands, Israel, E. spinosa occurs only in habitats where water runoff collects in sufficient quantities that ensure it is only a limiting factor after the seedling stage has passed (Evenari et al., 1977). In the Omayed Biosphere Reserve, Egypt, it occurs within coastal sand dunes, salt marshes, non-saline depressions, inland ridges, inland plateaux and on rain-fed farms in the area but not in saline depressions (Shaltout, 2003).

Where introduced, E. spinosa occupies highly disturbed areas. It is reported on roadsides in Australia (Weiss and Julien, 1975), along roads and railways in Kenya (Graham, 1958), in field borders and in waste sandy places in Pakistan (Siddiqi, 1973), along field drains in India (Varma et al., 1984), around homesteads and watering points in Australia (Gilbey, 1990), in areas of cultivation in the cereal-growing areas of upland Kenya (Agnew, 1974) and Australia (Weiss and Simmons, 1977) and near vine-fruit drying racks in Australia (Weiss and Julien, 1975; Weiss, 1977). E. spinosa is not normally predicted to become a weed of significance within grass-dominated ecosystems (Panetta and Mitchell, 1991; Panetta and Randall, 1993); however, when introduced to Hawaii, E. spinosa rapidly invaded rangelands (Goeden, 1978) becoming plentiful within semi-arid zones (500-875 mm/year) (Carlson, 1952). Rainfall patterns in the semi-arid zone allow for only 5-8 months of green foliage and this, coupled with overgrazing by early livestock, resulted in massive erosion problems in this zone (Carlson, 1952). E. spinosa grew thickest in the bare areas created by the stock (Fullaway, 1958). However, in the sub-humid zone (>750 mm/year) erosion was not a serious problem because there was usually sufficient plant cover. The sub-humid zone can be similar in elevation (200-800 m) and has the same nutrient-rich, red, ashy, basaltic soils as occur in the semi-arid zone, but E. spinosa did not occur within the semi-humid (or humid) zones (Carlson, 1952). Scattered E. spinosa plants occurred within the water stressed coastal flats <500 mm/year) and within the arid zones < 625 mm/year).

Habitat List

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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 Harmful (pest or invasive)
Rail / roadsides Present, no further details Harmful (pest or invasive)
Urban / peri-urban areas Present, no further details
Terrestrial ‑ Natural / Semi-naturalRiverbanks Present, no further details Harmful (pest or invasive)
Deserts Present, no further details Harmful (pest or invasive)
Littoral
Coastal areas Present, no further details Harmful (pest or invasive)

Hosts/Species Affected

Top of page Holm et al. (1979) report that in the native range countries of Egypt, Israel, Morocco and Portugal, E. spinosa is common but not likely to seriously threaten a crop. Within other Mediterranean countries, E. spinosa is widespread and, being a weed of disturbed environments, can potentially affect many crops with varying levels of impact. A detailed literature search (Scott and Beasley, 1996) detected only a few journal articles specifically noting E. spinosa as a pest of specific crops within its native range. However, E. spinosa has been reported as a weed of sugarbeet in Libya (Siwicki, 1967), in sesame in Egypt (Ibrahim et al., 1988), in apple orchards, lettuce, Chinese cabbage and wheat in Israel (Koren and Arenstein, 1973; Lifshitz et al., 1987a,b; Hadar et al., 1999), in tomatoes in Morocco (Rzozi, 1999; Tei et al., 1999), and in citrus groves in Iran, Turkey, the Near East and North Africa (Bischof, 1978).

In Hawaii it is recorded as infesting vegetables and low growing crops (Goeden, 1978) although the specific species are not mentioned, and in wheat-growing areas in upland Kenya (Agnew, 1974). In Australia, E. spinosa plants are usually found growing amongst E. australis plants within grain-growing agriculture areas (Weiss, 1977; Williams et al., 1984) with total densities of >300 Emex plants/m² common in both the grain crops and the legume-based pastures that are grown in rotation with the crops (Weiss, 1977). E. spinosa, has the potential to contaminate grain from cereal crops (Gilbey, 1974; Weiss and Julien, 1975) and there are stringent, near-zero tolerances on the level of contamination that is acceptable within cereal produce in both Morocco (WANA, 2001) and Australia (Bowran, 1996; Fromm, 1996). Screening is made difficult because achene size in E. spinosa is similar to the size of the grain from cereal crops and in some incidences grain has been rejected because it was not possible to satisfactorily remove the E. spinosa achenes present (Weiss and Simmons, 1977).

Host Plants and Other Plants Affected

Top of page

Growth Stages

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

Biology and Ecology

Top of page Genetics

The chromosome number (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 hybridize, with hybrids growing more vigorously than either parent but are completely sterile when self-pollinated (Putievsky et al., 1980). They were, however, able to backcross with the parental species giving the possibility of gene flow between the species. Due to the more erect morphology of E. spinosa and as both species are monoecious, seeds collected from E. australis plants were commonly outcrossed with E. spinosa, but seeds collected from E. spinosa were only rarely outcrossed with E. australis (Putievsky et al., 1980). All known Australian populations of E. spinosa were found to have a total lack of intra-populational isozyme variation (Marshall and Weiss, 1982) whereas a limited data set tested by the same authors found genetic variability within Mediterranean populations. The Australian populations did, however, vary in their multilocus genotypes, suggesting that there have been at least four separate introductions of the plant into Australia.

Physiology and Phenology

E. spinosa plants have a high degree of phenotypic plasticity because the plants have indeterminate growth, with stem production continuing as long as the conditions are suitable and aerial achene production being correlated with this stem and node production. Stem growth, flower and subsequent aerial seed production is continuous throughout the lifetime of the plant and the duration of this is dependent upon the environmental conditions. Flowers/aerial achenes form at the stem nodes as they are produced and under favourable growing conditions, plants may exceed 80 cm in height (Weiss and Julien, 1975) and contain >200 nodes and >1100 aerial achenes (Putievsky et al., 1980). E. spinosa growing in the least favourable habitat produced only 0.76 g (dry weight) of shoot and 16.2 aerial achenes whereas those in the most favourable habitat produced 20.2 g of shoot and 434.4 aerial achenes. There was only a comparatively small increase in the number of subterranean achenes produced (3.2 verses 4.6 seed/plant respectively) (Weiss, 1980). Only low numbers (1-10) of subterranean achenes are produced per plant and this occurs whilst the plant is still at the rosette stage (Evenari et al., 1977; Weiss, 1980).

With increased nitrogen from 5 to 50 kg/ha, there was a decrease in the root/shoot ratio of E. spinosa from 0.73 to 0.28 and there were large increases in the weight of total accumulated dry matter (0.7 versus 10.2 g/plant) and in aerial seed production (4 versus 342 seeds/plant) (Weiss, 1980). There was a only a small increase in the number of subterranean achenes per plant when soil nitrogen levels increased. The proportion of resources allocated into achene production (subterranean and aerial combined) was approximately 47% of the total dry weight regardless of nitrogen availability. However, at low soil nitrogen levels, 81% of the resources allocated to achene production was apportioned to the subterranean achenes whereas with high soil nitrogen levels, the subterranean achenes only accounted for 4.6% of the total dry matter used for achene production. Increased intra-specific plant competition (a six fold increase in density) resulted in E. spinosa plants producing fewer but larger subterranean achenes (6.4 achenes/plant with average weight of 73.4 mg versus 10.2 achenes/plant with average weight of 63.4 mg). The aerial achenes also decreased in abundance with increased plant densities (142 versus 477 achenes/plant) but the average size of the achene was not influenced (average weight of 13.6mg/achene in all treatments) (Weiss, 1980). Weiss (1980) also found soil nitrogen levels have no effect on the rate the plants mature with plants starting to produce subterranean achenes at 3.5 weeks of age and aerial achenes at 5.6 weeks of age independently of their nutritional status. In all treatments, plants had nearly fully senesced within 10 weeks of emergence.

Weiss (1980) also used potted E. spinosa plants and found that when grown together, plants derived from subterranean seeds were far more competitive than those derived from aerial seeds, having significantly more leaf area (500 cm²/plant verses 80 cm²/plant) 5 weeks after germination and producing almost 10 times more seed (840 achenes verses 90 achenes/plant) when initially planted at equal seedling densities. If grown under the same conditions but as a monoculture of either plants all from subterranean achenes or all from aerial achenes, there were no longer any differences due to the achene type with all plants having 200 cm² leaf area at 5 weeks of age and all plants producing 980 achenes.

E. spinosa plants however have several strong colonizing characteristics including drought tolerance, rapid growth, abundant seed production, seed dormancy and high dispersal abilities. Emex spinosa is able to colonize and then persist and even thrive within extremely hostile and unpredictable habitats primarily because of the two types of achenes (i.e. being amphycarpous). Subterranean achenes are produced in low numbers under all conditions maximizing the progeny's fitness and competitiveness whilst sacrificing some colonizing characteristics. Aerial achenes are produced in large numbers in response to favourable growing conditions maximizing the colonizing characteristics of the species at the cost of competitiveness and fitness.

The initial and rapid production of a few large, non-dispersing subterranean achenes ensures that the fittest progeny reappear at a site that has already proven itself to be suitable for the species. The long-term viability of the seeds, with their staggered emergence so that only one or two progeny from the same mother plant germinate in any particular year, safeguards against the occasional season that is unsuitable for reproduction even in previously proven habitats. Non-dormant seeds germinate rapidly in response to moisture and their comparatively large energy reserves allow them to rapidly establish a deep taproot and to themselves produce subterranean seed thus giving the species a high degree of drought proofing. The mother plant further contributes to the survival of these subterranean achenes by favourably modifying their microhabitat as when the mother plant dies, her taproot/crown shrinks to leave a hollow tapered cavity that can collect/trap water the following season (Weiss, 1980).

The subsequent reallocation of available resources into the production of numerous but small, highly dispersible aerial achenes facilitates the establishment of the plant in new or unoccupied locations; however, the comparatively low parental investment in each achene results in progeny that are not very vigorous or competitive and that are unlikely to survive in the presence of either conspecific plants derived from subterranean achenes or plants from other more competitive plant species.

Reproductive Biology

E. spinosa only reproduces by seed, is polygamo-monoecious (Zohary, 1966) and self-compatible. Shortly after pollination, the fruits formed in the axils of the rosette leaves start to develop, but the plant's contractile fleshy tap root pulls the young fruit below the soil surface where they complete development, becoming 'subterranean' achenes (von Murbeck, 1901). Further female and male flowers form at the nodes subsequently produced where the petioles attach to the stems and from these flowers, the 'aerial' achenes are produced. Individuals growing under poor field conditions (or in a short growing season) produce only a few seed <10) at the crown, but the same plant is capable of producing over 1000 seeds given favourable conditions (Evenari et al., 1977; Weiss, 1980), with Putievsky et al. (1980) recording an average of 1188 seeds per plant. Seeds from Emex spp. have a lengthy but compulsory after-ripening period (Hagon and Simmons, 1978) so that when early rains occur some seed produced in the previous season are not yet at a suitable physiological state for germination. This makes control of Emex more difficult as new waves of seedlings may emerge with each subsequent major rainfall events throughout the season (Weiss, 1981). The presence of a proportion of achenes with long-term innate dormancy also results in a seed bank that can persist for years (Evenari et al., 1977; Weiss, 1980; 1990).

E. spinosa seeds, like those of E. australis, are innately dormant when freshly formed and require an after-ripening period before germination is possible. Hagon and Simmons (1978) estimated the required after-ripening period, and with storage at 45/20°C day/night temperature, germination was 0%, 12% and 48% after 12, 18 and 24 weeks respectively, whereas at 60/20°C, germination had increased to 3.3%, 73% and 92% over the same periods. The achenes of E. spinosa are known to remain viable in the soil for many years and showed almost no mortality when stored in cardboard boxes at room temperatures for 7 years (Evenari et al., 1977); however, most studies on the persistence of viable Emex seed within the seed bank address E. australis and not E. spinosa. In Australia, where both species coexist, the degree of dormancy varies with the collection site, but the achenes from E. spinosa always have the higher rate of dormancy (Hagon, 1977). As E. australis seeds at some Australian sites are known to remain dormant within the soil for more than 8 years (Gilbey, 1996), this can be expected to also be possible for E. spinosa seeds.

Evenari et al. (1977) found that germination rates of seeds from the aerial achenes of E. spinosa decreased when in light. Germination rates of seeds from aerial achenes in general were low <24%) unless there were daily temperature fluctuations (15°C variations used) or the achenes were soaked in water for a couple of days. Germination rates of seeds from these leached aerial achenes peaked at 60% for seeds in the dark at 20°C and 50% for seeds in the light at 25°C. These germination pre-requirements, together with the ability of the aerial achenes to disperse widely and to remain viable for many years, permit the plant to colonize areas that are only periodically suitable for successful reproduction, thereby reducing the possibility of competition, whilst ensuring germination only occurs in favourable microhabitats such as buried near the surface during favourable seasons, i.e. years with high rainfall. The same pre-requirements also result in aerial achenes germinating several days after subterranean achenes in response to suitable germination conditions. Weiss (1980) found 15% germination of subterranean seed occurred within 2 days at temperatures of 19-30°C and within 6 days with a 15/10°C day/night temperature. Aerial achenes required 4 and 8 days respectively, to acquire the same level of germination at these temperatures.

Weiss (1980) found the subterranean achenes of E. spinosa differ from the aerial achenes in that they require a shorter after-ripening period (5 months instead of 8 months). Evenari et al. (1977) found that the germination rates of seed from subterranean achenes was low <30%) even with fluctuating temperatures and/or periods of leaching and that this ensured the germination of seeds from subterranean achenes from a single mother plant was spread over a long period of time. Physical damage to the subterranean achene stimulated germination and the authors consider this to be a 'last chance' event, seedlings being produced just prior to the seeds losing viability. Weiss (1980) found seeds from aerial achenes required light to stimulate germination, as would be experienced after cultivation/soil disturbances, whereas the subterranean seeds germinated equally well in light or darkness enabling them to germinate at the site of their mother plant without disturbance.

Seeds from achenes on the soil surface do not germinate (Weiss, 1980) and in E. australis which has similar but larger achenes, this is thought to be due to an inability to imbibe sufficient moisture when partially exposed (Cheam, 1987). Emergence rates from achenes buried 8 cm below the soil surface were significantly better from subterranean achenes (28%) than from aerial achenes (0%), but emergence rates were best for both types of achene when they were buried closer to the surface (approximately 80% for subterranean achenes and 60% for aerial achenes buried 1-4 cm deep) (Weiss, 1980). Seedlings derived from subterranean achenes are also more vigorous than those from aerial achenes after emergence. Evenari et al. (1977) grew potted plants from both types of seeds and at 3 weeks of age the seedlings from the subterranean achenes had a root system that was twice as deep as that of seedlings from aerial achenes, and they carried two or sometimes three true leaves rather than only one. Plants derived from subterranean achenes also produced aerial achenes much quicker than those derived from aerial achenes with the former possessing ripe aerial achenes when the latter were only just beginning to develop flowers upon their stems.

Environmental Requirements

A prerequisite to invading a new habitat is the ability to tolerate the new climatic conditions. Values estimated in the Climate table are derived from long-term climatic averages recorded for sites known to be at the edge of the known distribution range for E. spinosa in Australia (Marshall and Weiss 1982), southern Europe (Jalas and Suominen 1979), Israel (Zohary 1966), and Egypt (Kosinova 1974). Evenari et al. (1977) observed E. spinosa populations growing within the marginal habitats of the Avdat floodplains, Israel over a period of years. In a comparatively flat area that was not especially suited for the collection of runoff water, as little as 51 mm annual rainfall was enough for some E. spinosa plants to germinate and produce subterranean but not aerial achenes. With 29 mm annual rainfall, there was not enough moisture to allow germination and with 165 mm annual rainfall there was good germination and the production of both mature subterranean and aerial achenes. In some areas of the Avdat floodplain, water runoff collects even in drought years due to topographical reasons and in these locations E. spinosa is also present every year.

Weiss and Simmons (1977) studied the effects of photoperiod and temperature on growth and development in E. spinosa using potted plants within controlled environments. The optimum temperature for production of seed, stems and leaves was 11.7°C and for roots at 16.7°C. A delayed flowering and necrosis of stems were shown at the lowest (6.7°C) and highest (26.7°C) temperatures tested. Seed production at the highest temperatures (26.7°C) was approximately 9% of that observed at the optimal temperature of 12.7°C. A very strong positive correlation exists between temperature and rate of development until the temperature reaches approximately 19°C, with a negative correlation above this.

Williams et al. (1984) found that when grown in the presence of wheat, E. spinosa was weaker than E. australis as a competitor and both species of Emex were less competitive than wheat at low soil nitrogen levels. At high soil nitrogen levels, E. spinosa was still less competitive that wheat but E. australis became more competitive. These findings are consistent with the facts that on a global scale, E. australis has become a serious weed in several countries whereas E. spinosa is not a very weedy species anywhere (Holm et al., 1979; Pheloung et al., 1996). In Australia where both species have occurred sympatrically in several locations for more than 30 years (Putievsky et al., 1980; Marshall and Weiss, 1982), E. australis remains the more serious of the two weeds (Williams et al., 1984; Pheloung et al., 1996). Although E. spinosa usually occurs near sea level in the Mediterranean basin (Bischof, 1978), specimens have been collected from as high as 2660 m in Ecuador (Missouri Botanical Garden, 2003).

Associations

In the Negev, Israel, E. spinosa is found on loessial flood plains as a component of Hammada scoparia and Anabasis haussknechtii communities (Evenari et al., 1977). In Sousse, Tunisia, E. spinosa is common within Chenopodion muralis dominated nitrophilous plant communities within the town, in association with the thistles Onopordum arenarium and Carduus pteracanthus on the outskirts of town and with Lavatera cretica within the sand dunes (Brandes, 1991). In Australia, E. spinosa usually grows amongst E. australis within a cereal crops/pasture rotational farming system or on roadsides near vineyards (Weiss and Julien, 1975; Weiss and Simmons, 1977).

Air Temperature

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Parameter Lower limit Upper limit
Absolute minimum temperature (ºC) 0
Mean annual temperature (ºC) 18 21
Mean maximum temperature of hottest month (ºC) 25 36
Mean minimum temperature of coldest month (ºC) 6 12

Rainfall

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ParameterLower limitUpper limitDescription
Dry season duration57number of consecutive months with <40 mm rainfall
Mean annual rainfall51600mm; lower/upper limits

Rainfall Regime

Top of page Bimodal
Winter

Soil Tolerances

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Soil drainage

  • free

Soil reaction

  • acid
  • alkaline
  • neutral

Soil texture

  • heavy
  • light
  • medium

Special soil tolerances

  • infertile

Natural enemies

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Natural enemyTypeLife stagesSpecificityReferencesBiological control inBiological control on
Apion frumentarium Herbivore Leaves/Stems
Apion neofallax Herbivore Leaves/Stems
Apion violaceum Herbivore Leaves/Stems
Cercospora tripolitana Pathogen Leaves
Coniocleonus excoriatus Herbivore Leaves/Stems
Dysaphis emicis Herbivore Roots/Stems
Haploprocta sulcicornis Herbivore Stems
Lixus cribricollis Herbivore Leaves/Stems
Peronospora rumicis Pathogen Leaves/Stems

Notes on Natural Enemies

Top of page Surveys for insects associated with E. spinosa have been made in Morocco, Portugal (Krauss, 1963) and Israel (Scott and Shivas, 1990). Other insects, the weevils Coniocleonus excoriatus, Lixus cribricollis, Perapion neofallax, and Perapion violaceum, the aphid Dysaphis emicis, and the coreid bug Haploprocta sulcicornis are commonly found on plants in its indigenous range and have been proposed for assessment as biological control agents (Scott and Yeoh, 1996). Many of these species also include Rumex as host plants. Pathogens reported from E. spinosa from its indigenous range include Cercospora tripolitana (Hasan, 1979), and Peronospora rumicis (Viennot-Bourgin, 1969). There have been no studies of natural enemies in the introduced range. The weevils Lixus cribricolis (Julien et al., 1982) and Apion miniatum (Yeoh et al., 2002) are the only species from E. spinosa assessed and released in Australia as biological control agents.

In the late 1980s and early 1990s, farmers in Australia reported E. australis plants with distorted leaves that developed a yellow chlorosis and died before setting viable seed. These symptoms were referred to as "doublegee decline" but were later found to be caused by an aphid, Brachycaudus rumexicolens, thought to be native to North America and an insect that was not intentionally introduced into Australia (Berlandier and Scott, 1993; Scott et al., 1994). Brachycaudus rumexicolens has a widespread distribution within Australia and its predicted distribution range (Scott and Yeoh, 1999) overlaps with the known distribution range for E. spinosa (Marshall and Weiss, 1982). Under laboratory conditions, B. rumexicolens readily attacks both E. spinosa and E. australis (Scott and Yeoh, 1998) and although there are no published data on its impact on naturalized populations of E. spinosa, it can cause a 30% reduction in seed weight of E. australis plants growing in pasture and a 80% reduction in seed number in E. australis plants grown in a glasshouse (Yeoh and Scott, 1996). There are also records of B. rumexicolens occurring in Portugal, Spain, Italy, Turkey and the Canary Islands (Berlandier and Scott, 1993) where the aphid was usually collected from Rumex spp. It should, however, also be affecting E. spinosa populations in all these Mediterranean countries as again, the predicted distribution range of the aphid (Scott and Yeoh, 1999) overlaps the known distribution of E. spinosa (Jalas and Suominen, 1979) in this region.

Means of Movement and Dispersal

Top of page Natural Dispersal (Non-Biotic)

The large smooth and heavy subterranean achenes of E. spinosa are unlikely to move away from their site of origin; however, the aerial achenes are designed specifically for dissemination. Ripe aerial achenes detach from the parental plant either as separate units or in clusters on broken bits of the dead branch. As they are small and light, they are readily dispersed by strong winds or water and very few germinate in the immediate vicinity of their mother plant (Evenari et al., 1977).

Vector Transmission (Biotic)

E. spinosa has hard thorny achenes that lie on the ground so that one thorn is always pointing upwards. The spines are slightly reflexed so that they can also hook onto passing objects and the erect habit of the plant would encourage dissemination by this method. Fullaway (1958) notes that in Hawaii, cattle dispersed E. spinosa achenes that attached to their feet. Within the desert habitats of Israel, Evenari et al. (1977) observed various animals spreading the aerial achenes.

Accidental Introduction

The spiny achenes also facilitate the spread of the seed via human activity and the early Portuguese explorers accidentally transported them across the world, including Brazil, on their travels (Steinheil, 1838). There have been at least four separate introductions of E. spinosa into Australia (Marshall and Weiss, 1982).

The achenes readily adhere to objects such as shoes and the tyres of vehicles such as cars, aircraft and machinery. As Gilbey (1974) points out, the spines of E. spinosa are shorter and less robust than those of E. australis, which may explain the slower rates of spread of E. spinosa within Australia. Although the E. spinosa achenes are less likely than E. australis achenes to impale and then remain attached to broad, flat rubber surfaces such as the soles of shoes, their smaller size allows them to wedge between the treads of shoes and tyres. From the patterns of infestations, Weiss and Julien (1975) suspect vehicles transported E. spinosa achenes around within the dried fruit production area of Merbein, Victoria, Australia and achenes from both E. australis and E. spinosa are stated to be disseminated by cars in Hawaii (Goeden, 1978).

As the spread of E. spinosa infestations across Western Australia follow the old stock routes, Gilbey (1974) suspected E. spinosa was introduced as a contaminant of fodder. E. spinosa seeds contaminate grain produce (Gilbey, 1974; Weiss and Julien, 1975) and limits exist on the maximum contamination levels allowed with cereal crops in Australia (Bowran, 1996; Fromm, 1996) and Morocco (WANA, 2001). In Hawaii, E. spinosa was thought to have been accidentally introduced with grass seed (Fullaway, 1958).

Intentional Introduction

Although E. spinosa has limited beneficial characteristics, it is unlikely to have been intentionally introduced anywhere because of the obnoxious, spiny achenes with their resilient properties that makes controlling the species difficult.

Pathway Vectors

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VectorNotesLong DistanceLocalReferences
Clothing, footwear and possessionsEarly explorers Yes
Containers and packaging - woodCrates and bags Yes
Land vehiclesCar tyres Yes
Plants or parts of plantsGrain and fodder Yes
Soil, sand and gravelTransport possible in soil but no documented incidences. Yes
Water Yes
Wind Yes

Plant Trade

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Plant parts liable to carry the pest in trade/transportPest stagesBorne internallyBorne externallyVisibility of pest or symptoms
Leaves seeds
Stems (above ground)/Shoots/Trunks/Branches seeds
True seeds (inc. grain) seeds

Impact Summary

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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 None
Native flora None
Rare/protected species None
Tourism Negative
Trade/international relations Negative
Transport/travel None

Impact

Top of page In Australia, the grain industry (cereals, pulses and oilseeds) has restrictions on the maximum allowable levels of contamination with Emex seed, from 0 (zero) Emex seed/500ml in malt barley in South Australia to 20 Emex seed/500ml in feed barley or lupins in Western Australia. In wheat, 8 Emex seed/500mls is the national maximum standard (Bowran, 1996). E. spinosa, with its erect growth habit and a seed size similar to grain makes it potentially a far larger problem to the Australian grain-growing industry than the currently widespread E. australis (Weiss and Simmons, 1977) if its distribution spreads from 'extremely localized' which it is at present (Pheloung et al., 1996).

Environmental Impact

Top of page In Hawaii, uncontrolled Emex form dense mats of vegetation that shade out and displace useful plants. They then dry up during early summer to leave hillsides devoid of living vegetation and subject to sheet erosion (Goeden, 1978).

Impact: Biodiversity

Top of page In the Santa Monica Mountains, USA, E. spinosa is present in Point Muga State Park (Chester et al., 2002) but the impact of the weed on biodiversity is not documented.

Social Impact

Top of page In non-agricultural situations, the spiny achenes of Emex spp. make them a problem within amenity areas such as sport fields and parks. However, they are usually restricted to car park areas, tracks and other highly disturbed areas (Fromm, 1996).

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
  • Negatively impacts tourism
  • Reduced amenity values
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 In Egypt, E. spinosa is a folk medicine used for stomach disorders and to relieve colic (Watt and Breyer-Brandwijk, 1962) as well as being exploited as livestock fodder and even for human consumption (Shaltout, 2003).

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 (achenes) with three thorny spines, arranged at 120° to each other with one always facing 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 highly dependent on environmental conditions (Weiss and Simmons, 1979). Gilbey (1974) and Gilbey and Weiss (1980) differentiate 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 that point horizontally or downwards (so as to be hook-like) and the lower half of the seed capsule is truncate 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 being reported in Parsons and Cuthbertson (1992). In E. australis, the aerial achene, 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 Cultural Control

Williams et al. (1984) state that because E. spinosa becomes more competitive with increased soil nitrogen levels, there will be an increased need for control on soils of high nitrogen status or where additional nitrogen is added as a fertiliser. In Jordan, chemical application costs are only 25% of that of hand weeding, but weeds within most of the dryland farming area remain controlled primarily by cultural methods including high seeding rates so as to out-compete the weeds, delaying cultivation until after the weeds have germinated and improving tillage methods so as to restrict vertical seed movements within the soil (Turk and Tawaha, 2003). Within horticulture, weed competition can cause high yield decreases with economic injury levels being near zero weeds/m² for some weeds within sown tomato crops. Transplanting of vegetable seedlings rather than direct sowing of seeds allows for more thorough weed control prior to planting and gives the crop a competitive advantage over the weeds. In Hawaii, prior to the use of biological control, heavy infestations where hoes were inadequate were ploughed and then Kikuyu grass (Pennisetum clandestinum) planted to suppress the weed (Fullaway, 1958; Nakao, 1966).

Mechanical Control

Hand hoeing was the common practice used for controlling weeds, including E. spinosa, in crops such as sesame in Egypt, however growers are now switching to herbicides because they are cheaper and more effective (Ibrahim, 1988). In rainfed cereal crops in Jordan, increases of >7% for wheat and >4% for barley were observed following hand weeding of E. spinosa (Turk and Tawaha, 2003), and supplemented tillage as a weed control method, but again hand weeding is no longer economical. In Hawaii, prior to the introduction and establishment of the biological agent P. antiquum, small infestations of E. spinosa were hand weeded. Cultivation can stimulate the germination of Emex spp. achenes by burying those resting on the soil surface or by bringing deeply buried achenes closer to the surface where aeration, light and fluctuating temperatures can break seed dormancy (Hagon and Simmons, 1978; Weiss, 1980). Emex seedlings can then be killed by either a herbicide or a follow-up cultivation (Pearce, 1973). In general, weed control by cultivation is usually more effective in years with early rather than late autumn rains as most have already germinated, but there is a limit as to how late crop planting can be delayed before insufficient soil moisture at the end of the growing season will reduce crop yields (Turk and Tawaha, 2003).

Chemical Control

Herbicide-resistant weeds are an increasing problem promoted by the heavy reliance on post-emergent herbicides and in particular by the persistent use of the same type of chemical. Weed management strategies should aim to minimize herbicide usage (e.g. by cultural methods), avoid the consecutive use of herbicides that belong to the same herbicide group, and realise 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.

As Emex seeds can remain viable in the seed bank for many years, it is important to note that methods of chemical control will only affect plants that germinate in the current season and control measures will need to be repeated annually to completely deplete the seed bank. The timing of the application of herbicides is critical for the control of E. spinosa, with spraying recommended whilst the plants are at the rosette stage (Bischof, 1978). For the physiologically, morphologically and ecologically similar E. australis, Gilbey (1990) advises that herbicides become ineffective if applied after the runners have formed and even if the plants are killed at this stage some achenes will have already formed near the crown and therefore already contributed to the seed bank.

Members of the Polygonaceae (including Emex spp.) are highly susceptible to dicamba, and it has proved effective in Hawaii (Motooka, 2002). To overcome the problems in using knapsack sprayers for herbicide application, a 'drizzle' method has been developed in which concentrated droplets of herbicides are squirted as a fine jet stream from up to 5 m away from the target weed which breaks up into large, sparsely distributed droplets that then drizzle onto the plant. By utilizing the drizzle method rather than conventional methods, labour requirements are reduced by 83-98%. Dicamba is registered for the control of E. spinosa within pastures, forests and non-cropping situations in Hawaii using this drizzle method (Motooka et al., 2002) and herbicide trials using this method gave >86% control even with unfavourable spraying conditions (Motooka, 2002) and the drizzle method is also to apply the non-specific herbicides glyphosate and hexazinone.

In Australia, E. spinosa infestations are usually mixed with E. australis (Weiss and Julien, 1975; Weiss and Simmons, 1977) although most publications that discuss the chemical control of Emex spp. in Australia actually discuss only the control of E. australis (Gilbey, 1974; 1990; 1996) presumably due to the apparent lack of herbicides that are specifically registered for controlling E. spinosa. Parsons (1992) lists 104 products that are registered for use on E. australis but not one of these is listed for the control of E. spinosa. Fromm (1996) states that farmers in South Australia considered 'Emex spp.' to be less of a problem weed in 1991 than it was in 1985 because they were now controlled with sulfonylureas then available for use in the cereal phase of their rotational farming system.

Bischof (1978) makes a general comment that E. spinosa within the Mediterranean region can be controlled with MCPA or 2,4-D. In Jordan, however, Turk and Tawaha (2003) noted that "in hot, dry areas 2,4-D application is not recommended for wheat and barley because (of its) negative effect on yield and yield components" reporting decreases in yields of >22% for wheat and >8% for barley whereas hand weeding increased yields. In Morocco, metribuzin and pendimethalin are the authorized herbicides for E. spinosa control in tomato crops (Rzozi, 1999). In Libya, control of E. spinosa and other broadleaved weeds in sugar beet growing on irrigated sandy soils, pyrazon and lenacil are used (Siwicki, 1967) which are also widely used as a pre-emergent herbicide for the control of annual broadleaf weeds in beet crops throughout Europe (Thomson, 1989). However, so as to avoid crop damage, lower rates of application are recommended for use on sandy soils (Siwicki, 1967; Thomson, 1989). In Israel, the selective pre-emergent herbicide oxadiazon was effective for control of E. spinosa, other broadleaved weeds and grasses in transplanted Chinese cabbage (Lifshitz et al., 1987b), and pronamide alone, or in combination with oxadiazone, in transplanted iceberg lettuce (Lifshitz et al., 1987a). In Egypt, E. spinosa other annual broadleaved weeds are controlled by linuron or diuron, or for total control of all annual weeds, mixed with pendimethalin (Ibrahim et al., 1988).

Biological Control

In Australia, E. australis is a serious weed and in order to suppress this species, attempts have been made to import and establish biological control agents that attack Emex spp., including those from E. spinosa (Scott and Yeoh, 1996; Yeoh et al., 2002). Perapion antiquum, a weevil from E. australis in South Africa, was released on four islands in Hawaii providing substantial to complete control at 600-1200 m elevation (Julien and Griffiths, 1998) whereas two other weevils, Perapion neofallax and Perapion violaceum were also released but did not establish. Unlike the situation in Hawaii, E. spinosa continues to exist in Australia without impact from any of its native biological control agents. Perapion antiquum was released extensively in Australia during the 1970s and 1980s and establishment was recorded at one site but no control was achieved; climatic reasons have been suggested for the different degrees of success in Hawaii and Australia (Scott, 1992).

Surveys for insects associated with E. spinosa have been made in Morocco, Portugal (Krauss, 1963) and Israel (Scott and Shivas, 1990). Other insects, the weevils Coniocleonus excoriatus, Lixus cribricollis, Perapion neofallax, and Perapion violaceum, the aphid Dysaphis emicis, and the coreid bug Haploprocta sulcicornis are commonly found on plants in its indigenous range and have been proposed for assessment as biological control agents (Scott and Yeoh, 1996). Many of these species also include Rumex as host plants. Pathogens reported from E. spinosa from its indigenous range include Cercospora tripolitana (Hasan, 1979), and Peronospora rumicis (Viennot-Bourgin, 1969). There have been no studies of natural enemies in the introduced range. The weevils Lixus cribricolis (Julien et al., 1982) and Apion miniatum (Yeoh et al., 2002) are the only species from E. spinosa assessed and released in Australia as biological control agents.

Integrated Control

Integrated weed management programmes for tomato crops in Europe and Israel utilize weed control methods such as false seedbed preparations together with mechanical (harrowing, hoeing, split hoes etc) and/or chemical weed control methods (Tei et al., 1999). In Morocco where E. spinosa is a major weed of transplanted tomatoes in plastic tunnels, they are hoed 3-4 times with no herbicide usage whereas for crops in the open fields hoeing occurs 1-2 times with 5-80% of the total area treated with herbicides, depending upon rainfall (Rzozi, 1999).

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