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Datasheet

Phalaris aquatica (bulbous canarygrass)

Summary

  • Last modified
  • 22 June 2017
  • Datasheet Type(s)
  • Invasive Species
  • Preferred Scientific Name
  • Phalaris aquatica
  • Preferred Common Name
  • bulbous canarygrass
  • Taxonomic Tree
  • Domain: Eukaryota
  •   Kingdom: Plantae
  •     Phylum: Spermatophyta
  •       Subphylum: Angiospermae
  •         Class: Monocotyledonae
  • Summary of Invasiveness
  • P. aquatica, a perennial grass which can form large clumps and has short rhizomes around the base, has been extensively used as a pasture forage plant. From its native range around the Mediterranean it has been...

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Pictures

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PictureTitleCaptionCopyright
Phalaris aquatica (bulbous canary grass); habit, with a large plant growing on a roadside.
TitleHabit
CaptionPhalaris aquatica (bulbous canary grass); habit, with a large plant growing on a roadside.
Copyright©Trevor James/Hamilton, New Zealand-2015
Phalaris aquatica (bulbous canary grass); habit, with a large plant growing on a roadside.
HabitPhalaris aquatica (bulbous canary grass); habit, with a large plant growing on a roadside.©Trevor James/Hamilton, New Zealand-2015
Phalaris aquatica (bulbous canary grass); habit, with a large plant growing around a power pole.
TitleHabit
CaptionPhalaris aquatica (bulbous canary grass); habit, with a large plant growing around a power pole.
Copyright©Trevor James/Hamilton, New Zealand-2015
Phalaris aquatica (bulbous canary grass); habit, with a large plant growing around a power pole.
HabitPhalaris aquatica (bulbous canary grass); habit, with a large plant growing around a power pole.©Trevor James/Hamilton, New Zealand-2015
Phalaris aquatica (bulbous canary grass); habit, with a large flowering plant growing on a roadside.
TitleHabit
CaptionPhalaris aquatica (bulbous canary grass); habit, with a large flowering plant growing on a roadside.
Copyright©Trevor James/Hamilton, New Zealand-2015
Phalaris aquatica (bulbous canary grass); habit, with a large flowering plant growing on a roadside.
HabitPhalaris aquatica (bulbous canary grass); habit, with a large flowering plant growing on a roadside.©Trevor James/Hamilton, New Zealand-2015
Phalaris aquatica (bulbous canary grass); flowerhead.
TitleFlowerhead
CaptionPhalaris aquatica (bulbous canary grass); flowerhead.
Copyright©Trevor James/Hamilton, New Zealand-2015
Phalaris aquatica (bulbous canary grass); flowerhead.
FlowerheadPhalaris aquatica (bulbous canary grass); flowerhead.©Trevor James/Hamilton, New Zealand-2015
Phalaris aquatica (bulbous canary grass); flowerhead, with emergent anthers.
TitleFlowerhead
CaptionPhalaris aquatica (bulbous canary grass); flowerhead, with emergent anthers.
Copyright©Trevor James/Hamilton, New Zealand-2015
Phalaris aquatica (bulbous canary grass); flowerhead, with emergent anthers.
FlowerheadPhalaris aquatica (bulbous canary grass); flowerhead, with emergent anthers.©Trevor James/Hamilton, New Zealand-2015
Phalaris aquatica (bulbous canary grass); close-up of flowerhead, with emergent anthers.
TitlePhalaris aquatica (bulbous canary grass); flowerhead with emergent anthers.
CaptionPhalaris aquatica (bulbous canary grass); close-up of flowerhead, with emergent anthers.
Copyright©Trevor James/Hamilton, New Zealand-2015
Phalaris aquatica (bulbous canary grass); close-up of flowerhead, with emergent anthers.
Phalaris aquatica (bulbous canary grass); flowerhead with emergent anthers.Phalaris aquatica (bulbous canary grass); close-up of flowerhead, with emergent anthers.©Trevor James/Hamilton, New Zealand-2015
Phalaris aquatica (bulbous canary grass); collar area, showing the ligule.
TitlePhalaris aquatica (bulbous canary grass); collar area, showing the ligule.
Caption
Copyright©Trevor James/Hamilton, New Zealand-2015
Phalaris aquatica (bulbous canary grass); collar area, showing the ligule.
Phalaris aquatica (bulbous canary grass); collar area, showing the ligule.©Trevor James/Hamilton, New Zealand-2015
Phalaris aquatica (bulbous canary grass); bulbous base of a shoot.
TitleBulbous shoot base
CaptionPhalaris aquatica (bulbous canary grass); bulbous base of a shoot.
Copyright©Trevor James/Hamilton, New Zealand-2015
Phalaris aquatica (bulbous canary grass); bulbous base of a shoot.
Bulbous shoot basePhalaris aquatica (bulbous canary grass); bulbous base of a shoot.©Trevor James/Hamilton, New Zealand-2015

Identity

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Preferred Scientific Name

  • Phalaris aquatica L.

Preferred Common Name

  • bulbous canarygrass

Other Scientific Names

  • Phalaris stenoptera Hack.
  • Phalaris tuberosa L.

International Common Names

  • English: Australian phalaris; bulbous canary grass; Harding grass; Hardingrass; phalaris; Toowoomba canary grass
  • Spanish: rabillo de cordero
  • French: alpiste bulbeux; herbe de Harding; phalaris tubéreux
  • Chinese: shui ge cao

Local Common Names

  • Germany: knolliges Glanzgras
  • Japan: hädhingu-gurasu
  • Portugal: capini-doce
  • Sweden: knölflen

Summary of Invasiveness

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P. aquatica, a perennial grass which can form large clumps and has short rhizomes around the base, has been extensively used as a pasture forage plant. From its native range around the Mediterranean it has been introduced to several parts of the world, notably North America and Australia. In these countries it has been sown as a pasture species or for revegetation after burning, and has naturalized and spread widely. It outcompetes and displaces native plant species. Tall stands of dry foliage present a fire risk in summer. In Australia it is regarded as an environmental weed in Victoria, New South Wales and South Australia, and as a priority environmental weed in three Natural Resource Management regions.

Taxonomic Tree

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  • Domain: Eukaryota
  •     Kingdom: Plantae
  •         Phylum: Spermatophyta
  •             Subphylum: Angiospermae
  •                 Class: Monocotyledonae
  •                     Order: Cyperales
  •                         Family: Poaceae
  •                             Genus: Phalaris
  •                                 Species: Phalaris aquatica

Notes on Taxonomy and Nomenclature

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Watson and Dallwitz (2015) mention 22 species of Phalaris found in northern temperate areas and South America, although the Plant List (2013) gives accepted names for only 19 species. Phalaris aquatica was long known as P. tuberosa; both names were given by Linnaeus but P. aquatica has precedence.

Description

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P. aquatica forms strong perennial clumps (unless kept grazed), 60-200 cm tall, arising from short knotted rhizomes. Shoots are swollen and tuberous at their bases. Flower stems have smooth internodes. Leaf sheaths are rounded on the back, firm, hairless, light brown or brownish-green. Ligules are 4-9 mm long, membranous, rounded. The leaf blade is hairless, green, tapered to a long fine point, 15-60 cm long, 5-11 mm wide, flat, smooth on the under surface, slightly rough on the margins. The inflorescence is a dense, stiff, cylindrical, spike-like panicle, oblong or slightly tapered top and bottom, 3.5-12 cm long, 0.8-2.5 mm across; main axis smooth, branches hidden. Spikelets are light green, 4.5-6.5 mm long, with two lower sterile florets and an upper fertile one, breaking above the glumes at maturity (from Champion et al., 2012).

Plant Type

Top of page Grass / sedge
Perennial
Seed propagated

Distribution

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Species of the genus Phalaris have now been taken to every continent except Antarctica. P. aquatica originated in countries around the Mediterranean and the Middle East and has been carried to several countries with comparable climates, most notably parts of the USA, Australia, South Africa and New Zealand. The strains taken to these countries mostly originated in North Africa.

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

AzerbaijanPresentNativeUSDA-ARS, 2015
China
-HunanPresentIntroducedFlora of China Editorial Committee, 2015
IraqPresentNativeUSDA-ARS, 2015
IsraelPresentNativeUSDA-ARS, 2015
LebanonPresentNativeUSDA-ARS, 2015
PakistanPresentIntroducedFlora of Pakistan, 2015
SyriaPresentNativeUSDA-ARS, 2015
TurkeyPresentNativeUSDA-ARS, 2015

Africa

AlgeriaPresentNativeUSDA-ARS, 2015
KenyaPresent only in captivity/cultivationIntroducedCLAYTON, 1970Identification uncertain, occurred near Naiavasha, Kiambu District and Muguga (Nairobi) in 1952-1953
LibyaPresentNativeUSDA-ARS, 2015
MoroccoPresentNativeUSDA-ARS, 2015
South AfricaPresentIntroducedUSDA-ARS, 2015
Spain
-Canary IslandsPresentNativeUSDA-ARS, 2015
TunisiaPresentNativeUSDA-ARS, 2015

North America

USAPresentIntroducedUSDA-NRCS, 2015
-ArizonaPresentIntroducedUSDA-NRCS, 2015
-CaliforniaPresentIntroducedUSDA-NRCS, 2015
-MississippiPresentIntroducedUSDA-NRCS, 2015
-MontanaPresentIntroducedUSDA-NRCS, 2015
-North CarolinaPresentIntroducedUSDA-NRCS, 2015
-OregonPresentIntroducedUSDA-NRCS, 2015
-South CarolinaPresentIntroducedUSDA-NRCS, 2015
-TexasPresentIntroducedUSDA-NRCS, 2015
-VirginiaPresentIntroducedUSDA-NRCS, 2015

South America

ArgentinaPresentIntroducedOram et al., 2009

Europe

AlbaniaPresentNativeUSDA-ARS, 2015
BulgariaPresentNativeUSDA-ARS, 2015
CroatiaPresentNativeUSDA-ARS, 2015
CyprusPresentNativeUSDA-ARS, 2015
FrancePresentNativeUSDA-ARS, 2015
GreecePresentNativeUSDA-ARS, 2015; USDA-ARS, 2015
IrelandPresentIntroducedUSDA-ARS, 2015
ItalyPresentNativeUSDA-ARS, 2015
PortugalPresentNativeUSDA-ARS, 2015
-MadeiraPresentNativeUSDA-ARS, 2015
SpainPresentNativeUSDA-ARS, 2015
UKPresentIntroduced1778Online Atlas of the British and Irish Flora, 2015; USDA-ARS, 2015

Oceania

AustraliaPresentIntroducedUSDA-ARS, 2015
-New South WalesPresentIntroduced Invasive Weeds of Australia, 2015Eastern areas, environmental weed
-South AustraliaPresentIntroduced Invasive Weeds of Australia, 2015South east areas, environmental weed
-TasmaniaPresentIntroducedWeeds of Australia, 2015
-VictoriaPresentIntroduced Invasive Weeds of Australia, 2015Environmental weed
-Western AustraliaPresentIntroduced Invasive Weeds of Australia, 2015South west areas, environmental weed
New ZealandPresentIntroducedEdgar and Connor, 2010

History of Introduction and Spread

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Barry (2007) summarizes the history of P. aquatica in California from the report by Adams and Kay (1985). The species was taken from North Africa to South Africa and then to Australia before being planted at the Californian Agricultural Experiment Station in 1914. In Australia the first herbarium record is from New South Wales in 1885 (Council of Heads of Australasian Herbaria, 2015).

Interestingly, Watson et al. (2000) tell a different story: “It was first introduced into Australia from the United States in 1884 under the name Phalaris commutata by Mr R. Harding, later the curator at Toowoomba Botanic Gardens, where it became known as Toowoomba Canary Grass for some time.” As a result “in the United States, the standard common name for phalaris is Harding Grass in recognition of Mr Harding’s efforts in evaluating and distributing phalaris”. This explains how the species became commonly known as Harding grass.

P. aquatica was first cultivated in Britain in 1778 where it was (and is) sown as cover and food for pheasants, and more rarely for grazing or silage. It was recorded in the wild by 1912 and seems to be increasing, especially in East Anglia and SE England (Online Atlas of the British and Irish Flora, 2015).

Introductions

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Introduced toIntroduced fromYearReasonIntroduced byEstablished in wild throughReferencesNotes
Natural reproductionContinuous restocking
California South Africa 1914 Forage (pathway cause) Yes Barry, 2007
New South Wales USA 1884-1885 Crop production (pathway cause) Yes Council of Heads of Australasian Herbaria, 2014; Watson et al., 2000
New Zealand 1940-1970 Crop production (pathway cause) Yes Esler, 1987 Naturalized by 1973
South Africa North Africa   Barry, 2007
UK 1778 Hunting, angling, sport or racing (pathway cause) Yes Online Atlas of the British and Irish Flora, 2015 Found naturalized in 1912

Risk of Introduction

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Although difficult to establish from seed, P. aquatica has successfully been cultivated in several countries on different continents and is likely to be further introduced to other countries with suitable environments.

Habitat

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P. aquatica is widespread in California as a result of its use as a forage species and for revegetation after fires. There it is most common in coastal valley and foothill grasslands from Oregon to the Mexican border (Harrington and Lanini, 2000). It is also found in the Sacramento and San Joaquin valleys below 1200 m. It often dominates the vegetation along infrequently cut roadsides and is also often found beside ditches and streams.

In Britain, to which P. aquatica was also introduced, it occurs in woodland glades, the borders of fields, along roadsides and in waste places (Online Atlas of the British and Irish Flora, 2015). It is also found as a casual on rubbish tips and waste ground.

In Australia, introduced P. aquatica is a weed of pastures, grasslands, open woodlands, roadsides, waste areas, disturbed areas, creek banks, riparian vegetation, floodplains and wetlands (Weeds of Australia, 2015). According to Watson et al. (2000), the species is adapted to a wide range of soils, from shallow, moderately acidic, sedimentary soils to deep, self-mulching alkaline clays; however, it grows best on deep, heavy-textured soils of high fertility or on soils that have received regular applications of phosphorus or sulfur or both.

Several authors mention its prevalence along roadsides and on low-lying, damper land, including drains (Harrington and Lanini, 2000; Richardson et al., 2006). The species may be spread along roadsides by mowers throwing the seed, and may also then spread into nearby fields.

Habitat List

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CategoryHabitatPresenceStatus
Terrestrial-managed
Cultivated / agricultural land Principal habitat Productive/non-natural
Disturbed areas Secondary/tolerated habitat Natural
Managed grasslands (grazing systems) Principal habitat Productive/non-natural
Rail / roadsides Secondary/tolerated habitat Natural
Terrestrial-natural/semi-natural
Natural forests Secondary/tolerated habitat Natural
Natural grasslands Secondary/tolerated habitat Natural
Riverbanks Secondary/tolerated habitat Natural
Wetlands Secondary/tolerated habitat Natural

Hosts/Species Affected

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In California, P. aquatica outcompetes and displaces native plant species (Harrington and Lanini, 2000). Where it occurs in Australia it presumably also replaces native grasses and other plants in the areas it invades.

Biology and Ecology

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Genetics

P. aquatica has a chromosome number of 2n = 28 (Flora of China Editorial Committee, 2015).

Reproductive Biology

Although plants of P. aquatica can spread outwards by means of their short rhizomes, the main way in which plants spread is by production of copious seeds. In California flowering occurs between May and June, with viable seed formed between May and September. Seed production varies with plant density, soil type and weather conditions, and can be as much as 40,000 seeds m-2 (Harrington and Lanini, 2000).

Physiology and Phenology

According to Peterson (2001) a summer dormancy period is needed before P. aquatica seeds can germinate, the length of the dormancy period varying widely depending on the genotype of the seed source. Seeds will germinate whenever moisture is available, but germination rates fall if temperatures are below 10oC or above 30oC. 

Plants are very deep-rooted, which helps them survive through droughts.

Longevity

Presumably, once well-established, individual plants of P. aquatica can survive for some years and dense stands of the species presumably sustain themselves through a combination of long-lived plants and reseeding (Peterson, 2001). In Australia the species has a reputation for its excellent persistence and drought tolerance – far better than that of other temperate pasture species like cocksfoot, fescue or perennial ryegrass (Watson et al., 2000).

Activity Patterns

P. aquatica grows weakly as a seedling but is an aggressive competitor once it is established (Peterson, 2001). Its most vigorous growth is in spring and autumn and it is quick to respond to early autumn rainfall. In summer it can enter a period of dormancy which can be broken if summer storms are followed by periods of cool or mild weather. This summer dormancy can be influenced by cultivar, management and climate (Watson et al., 2000).

Population Size and Structure

P. aquatica can form dense stands that outcompete and displace native vegetation (Harrington and Lanini, 2000).

Nutrition

P. aquatica grows best in high fertility conditions, but can tolerate low fertility soils (Lambrechtsen, 1975). Watson et al. (2000) report that, in Australia, “a productive phalaris pasture has very high requirements for nitrogen (N), phosphorus (P), potassium (K) and sulphur (S).” Nitrogen can be provided by either a strong legume component or regular dressings of nitrogenous fertilizer (Watson et al., 2000).

Associations

In Australia, where P. aquatica is commonly grown as a pasture species, it grows better if associated with a leguminous plant such as Trifolium subterraneum, Trifolium repens or Medicago sativa (Watson et al., 2000).

Environmental Requirements

Due to weak growth, P. aquatica seedlings will establish only if there is minimal competition. The species tolerates some shade, hence its occurrence in open woodlands (Peterson, 2001; Weeds of Australia, 2015), but prefers open ground (Harrington and Lanini, 2000). Watson et al. (2000), describing the requirements of P. aquatica as a cultivated pasture grass in Australia, note that it “is adapted to a wide range of soils from shallow, moderately acidic, sedimentary soils to deep, self-mulching alkaline clays. However, phalaris grows best on deep, heavy textured soils of high fertility, or soils having received regular applications of phosphorus or sulphur fertiliser, or both, to promote good clover growth which will meet the high nitrogen requirements of phalaris.” They continue: “It will persist in winter-dominant rainfall areas where the average annual rainfall is 500 mm. Phalaris is not very productive in districts with less than 500 mm except in very favourable situations. It is important for phalaris that most of this rain falls in autumn to late spring to coincide with its main growth period.”

P. aquatica is well adapted to mild, moist winters and hot, dry summers like those of its native Mediterranean and so is well suited to similar climates like those of south-west North America and southern Australia. In Australia it will persist where the average annual rainfall is 500 mm or more, with most falling in autumn to late spring (Watson et al., 2000). The species can survive low winter temperatures and severe frosts as well as high summer temperatures. It grows best at 15o to 25oC. It often shows a period of dormancy during the summer.

Climate

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ClimateStatusDescriptionRemark
Cf - Warm temperate climate, wet all year Preferred Warm average temp. > 10°C, Cold average temp. > 0°C, wet all year
Cs - Warm temperate climate with dry summer Preferred Warm average temp. > 10°C, Cold average temp. > 0°C, dry summers

Rainfall Regime

Top of page Winter

Soil Tolerances

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Soil reaction

  • acid
  • alkaline

Soil texture

  • heavy
  • medium

Special soil tolerances

  • shallow

Natural enemies

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Natural enemyTypeLife stagesSpecificityReferencesBiological control inBiological control on
Formicidae Herbivore Seeds not specific N/A N/A
Halotydeus destructor Herbivore Whole plant not specific N/A N/A
Penthaleus Herbivore Whole plant not specific
Teleogryllus commodus Herbivore Whole plant not specific

Notes on Natural Enemies

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In North America, Harrington and Lanini (2000) claim that no insects or fungi are known to be effective in controlling P. aquatica. However, in Australia, Watson et al. (2000) report that phalaris pastures are sometimes seriously damaged by blue oat mites (Penthaleus spp.), redlegged earth mites (Halotydeus destructor), aphids (various species), seed-harvesting ants (various species), field crickets (such as Teleogryllus commodus), white curl grubs (various species of scarab grubs), and slugs and snails during the establishment stage. Established phalaris pastures are usually more resistant to insect attack.

Means of Movement and Dispersal

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Natural Dispersal

According to DiTomaso and Healy (2003), seeds can be dispersed for short distances by animals and for greater distances by water.

Vector Transmission (Biotic)

In Australia harvester ants are well known distributors (and consumers) of the seeds of phalaris and other grasses (Watson et al., 2000).

Accidental Introduction

Although deliberately introduced to several countries where it has naturalized, its further spread within those countries has been by natural means, along roadsides and water courses (Harrington and Lanini, 2000). In Britain it has been accidentally introduced and dispersed as a wool, esparto and bird-seed alien and grass seed contaminant (Online Atlas of the British and Irish Flora, 2015).

Intentional Introduction

P. aquatica has been deliberately introduced to a number of countries for use as a forage crop. This use has been most marked in Australia and California but it has also been introduced to South American countries and to South Africa.

Pathway Causes

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CauseNotesLong DistanceLocalReferences
Animal production Yes Yes Barry, 2007
Forage Yes Yes Barry, 2007

Pathway Vectors

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VectorNotesLong DistanceLocalReferences
Hides, trophies and feathers Yes Yes
Host and vector organisms Yes
Livestock Yes
Plants or parts of plants Yes Yes
Water Yes

Plant Trade

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Plant parts liable to carry the pest in trade/transportPest stagesBorne internallyBorne externallyVisibility of pest or symptoms
True seeds (inc. grain) No No

Impact Summary

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CategoryImpact
Economic/livelihood Positive
Environment (generally) Positive and negative

Economic Impact

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The economic aspects of this species where it is sown as a forage crop are overwhelmingly positive. Its invasion into natural areas has very little economic effect other than the cost of control by government agencies or private individuals. Improved cultivars have been developed in Argentina, Greece, Israel, Tunisia (Oram et al., 2009), Australia (Watson et al., 2000), California (Dyer and O’Beck, 2005) and New Zealand (Rumball, 1980).

Where grown as a fodder, phalaris can often poison sheep, cattle, goats and horses. The causes and effects of such poisoning have been reviewed by Alden et al. (2014) and Connor (1977). These toxicoses present as either ‘phalaris staggers’ or ‘phalaris sudden death’. Although alkaloid toxins have been implicated in both, their identification and mechanism of action are still not fully understood. The average Australian phalaris farmer experiences outbreaks of poisoning between once every 4 years and once every 20 years (Alden et al., 2014). Some of the new cultivars have proven less toxic to livestock (Oram and Edlington, 1996).

Environmental Impact

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Impact on Habitats

In south-east Australia, Muyt (2001) reports that P. aquatica regularly spreads out from sown pastures, road verges and drainage ditches to invade indigenous vegetation. Once dense stands are established, most indigenous ground flora will be excluded and any overstorey recruitment of native species will be severely impeded. Similarly, in the USA, Harrington and Lanini (2000) note that this species spreads along roadsides, from where it spreads into nearby areas of native vegetation, where it can outcompete and displace native plant species.

Impact on Biodiversity

P. aquatica reduces native plant diversity in areas it invades.

Risk and Impact Factors

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Impact mechanisms

  • Competition - shading
  • Competition - smothering
  • Poisoning

Impact outcomes

  • Ecosystem change/ habitat alteration
  • Modification of successional patterns
  • Threat to/ loss of native species

Invasiveness

  • Benefits from human association (i.e. it is a human commensal)
  • Has high reproductive potential
  • Long lived
  • Proved invasive outside its native range
  • Reproduces asexually
  • Tolerant of shade
  • Tolerates, or benefits from, cultivation, browsing pressure, mutilation, fire etc

Uses

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Economic Value

There are more than 1.6 million ha of pasture containing phalaris in New South Wales; Watson et al. (2000) quoted district agronomists in 1990, indicating that the potential area of phalaris-based pastures in New South Wales was 3 million ha. In California too, substantial areas have been sown with the species, either for pasture or for establishing vegetation after fire (Harrington and Lanini, 2000).

Watson et al. (2000) mention a number of advantages of phalaris pastures, including: good quality grazing for cattle, sheep, goats and horses; plants are competitive and robust and resist invasions by many weeds; tolerance of extended periods of heavy grazing; excellent recovery after bush fires; good regrowth after attack by plague locusts and wingless grasshoppers; good field resistance to underground attack by soil-dwelling pests; good performance in poorly drained and waterlogged soils; excellent frost resistance and high productivity during winter; excellent resistance to livestock trampling; and quick response to autumn rainfall.

Social Benefit

Presumably the species improves the economy of the local farmers and their families in areas where it is grown.

Uses List

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Animal feed, fodder, forage

  • Fodder/animal feed
  • Forage

Environmental

  • Revegetation
  • Wildlife habitat

Similarities to Other Species/Conditions

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Harrington and Lanini (2000) comment on the similarity of P. aquatica to three other species of Phalaris found in North America (and elsewhere, including Australia and New Zealand), namely P. arundinacea, P. canariensis and P. minor. These authors report that the base of the stem of P. aquatica produces a reddish sap when cut, unlike the other species. In addition, the other three species have winged glumes, with the wing widest in the upper third of the glumes of P. canariensis and P. minor. The glume wing margins of P. minor usually have tiny teeth whereas the margins are entire in the other two species. P. canariensis and P. minor are both annuals, usually have shorter inflorescences and lack the tuberous swelling at the base of the stem of P. aquatica. P. arundinacea is a perennial, like P. aquatica, but has more distinct rhizomes and the inflorescence is compact at first but later becomes more open as the branches spread. Hybrids between P. aquatica and P. arundinacea have been produced.

Prevention and Control

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Control

Peterson (2001) reports that localized occurrences of P. aquatica should not be regarded as highly negative features in grasslands or other plant communities. If the plant community is relatively competitive with P. aquatica, then it should not pose a great threat and can probably be adequately controlled.

Cultural Control and Sanitary Measures

Areas where the native vegetation is healthy and vigorous ought to repel invasions by P. aquatica (Peterson, 2001)Harrington and Lanini (2000) claim that cultivation is generally not an effective control measure because P. aquatica is a prolific seeder and can also regenerate from small pieces of rhizome left in the soil. Repeated cultivation would be needed when the plants were actively growing. They add that cultivation may, however, be used to remove a flush of seedlings and this would also reduce the size of the seedbank. According to DiTomaso et al. (2013), grazing by livestock or geese can suppress P. aquatica growth and remove biomass, thus enhancing any herbicide applications. Burning of new shoots in early spring can suppress the weed, although it is not effective for total control. However, as with grazing, burning can make subsequent herbicide applications more effective by removing excess biomass (DiTomaso et al., 2013). Burning during winter can reduce subsequent growth for about 2 years (Peterson, 2001).

Physical/Mechanical Control

Hand pulling is practical only for small areas as it requires a large time commitment. It can be effective if done over the entire population 2-3 times every year for 5 years. Close mowing late in the season can reduce plant vigour and remove excess biomass to make chemical control more effective; regrowth should not be allowed before treatment (DiTomaso et al., 2013). Peterson (2001) points out that frequent removal of herbage during the active growth period of the grass reduces total biomass and increases mortality. According to the Bureau of Land Management of the US Department of the Interior (BLM, 2012), frequent clipping of P. aquatica during the active growth phase can be effective at preventing spread and reducing tillering. Clipping the grass later in the spring retards growth better than clipping at the beginning of flowering. Clipping at the end of the growing season when soil moisture is low reduces growth the following year.

Biological Control

Since P. aquatica is a valuable pasture species, any attempts at biological control are not likely to be welcomed by farmers.

Chemical Control

Several herbicides are effective at controlling P. aquatica but relatively high rates are required. Peterson (2001) found that 2,4-D amine, 2,4-D ester, dicamba and picloram all gave good control of six-week-old seedlings. Effective control of P. aquatica was noted in studies involving application of the approved herbicides clethodim, glyphosate and sulfometuron (DiTomaso et al., 2013). Some pre-emergent herbicides no longer approved for use in the EU gave good control in the past (Berry and Buchanan, 1974, quoted in Peterson, 2001). 

Monitoring and Surveillance (Incl. Remote Sensing)

Peterson (2001) says that areas requiring close monitoring are those close to private grazed land or weedy areas containing P. aquatica, as such places may pose a constant threat.

References

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Adams TE; Kay B, 1985. Perennial grasses for California rangelands. Davis, California, USA: UC Davis Department of Agronomy and Range Science. [Range Science Report No. 3.]

Alden R; Hackney B; Weston LA; Quinn JC, 2014. Phalaris toxicoses in Australian livestock production systems: prevalence, aetiology and toxicology. Journal of Toxins, 1(1):7.

Barry S, 2007. The history of Harding grass in California. Keeping Landscapes Working, 4(3):6-7. http://cesantaclara.ucanr.edu/news_719/Keeping_Landscapes_Working/?newsitem=25462

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05/05/2015  Original text by:

Ian Popay, Consultant, New Zealand

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