Invasive Species Compendium

Detailed coverage of invasive species threatening livelihoods and the environment worldwide

Datasheet

Poa annua
(annual meadowgrass)

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Datasheet

Poa annua (annual meadowgrass)

Summary

  • Last modified
  • 27 September 2018
  • Datasheet Type(s)
  • Invasive Species
  • Pest
  • Host Plant
  • Preferred Scientific Name
  • Poa annua
  • Preferred Common Name
  • annual meadowgrass
  • Taxonomic Tree
  • Domain: Eukaryota
  •   Kingdom: Plantae
  •     Phylum: Spermatophyta
  •       Subphylum: Angiospermae
  •         Class: Monocotyledonae
  • Summary of Invasiveness
  • P. annua is a cosmopolitan grass included in the Global Compendium of Weeds (Randall, 2012) and listed as one of the most aggressive weeds invading areas from sea level...

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Pictures

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PictureTitleCaptionCopyright
Poa annua (annual meadowgrass); habit. Netherlands. April  2005.
TitleHabit
CaptionPoa annua (annual meadowgrass); habit. Netherlands. April 2005.
Copyright©Rasbak/via wikipedia - CC BY-SA 3.0
Poa annua (annual meadowgrass); habit. Netherlands. April  2005.
HabitPoa annua (annual meadowgrass); habit. Netherlands. April 2005.©Rasbak/via wikipedia - CC BY-SA 3.0
Poa annua (annual meadowgrass); habit, showing flowers. Netherlands. April  2005.
TitleHabit
CaptionPoa annua (annual meadowgrass); habit, showing flowers. Netherlands. April 2005.
Copyright©Rasbak/via wikipedia - CC BY-SA 3.0
Poa annua (annual meadowgrass); habit, showing flowers. Netherlands. April  2005.
HabitPoa annua (annual meadowgrass); habit, showing flowers. Netherlands. April 2005.©Rasbak/via wikipedia - CC BY-SA 3.0
Poa annua (annual meadowgrass); habit, mature plant, usually 10-20 cm tall.
TitleHabit
CaptionPoa annua (annual meadowgrass); habit, mature plant, usually 10-20 cm tall.
Copyright©Chris Parker/Bristol, UK
Poa annua (annual meadowgrass); habit, mature plant, usually 10-20 cm tall.
HabitPoa annua (annual meadowgrass); habit, mature plant, usually 10-20 cm tall.©Chris Parker/Bristol, UK

Identity

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Preferred Scientific Name

  • Poa annua L.

Preferred Common Name

  • annual meadowgrass

Other Scientific Names

  • Aira pumila Pursh
  • Catabrosa pumila (Pursh) Roem. & Schult.
  • Ochlopoa annua (L.) H.Scholz
  • Poa aestivalis J.Presl
  • Poa algida Trin
  • Poa bipollicaris Hochst.
  • Poa hohenackeri Trin.
  • Poa meyenii Nees & Meyen
  • Poa ovalis Tineo
  • Poa puberula Steud.
  • Poa royleana Nees ex Steud.

International Common Names

  • English: annual bluegrass (USA, Canada, South Africa); annual wintergrass (Australia); goosegrass (Australia)
  • Spanish: champa; espiguela; espiguilla; hierba punta; pasto azul anual; pelosa; poa anual; zacate azul
  • French: paturin annuel
  • Chinese: chao-soo-hoo; zao shu he
  • Portuguese: cabelo-de-cão

Local Common Names

  • Argentina: pastillo de invierno
  • Brazil: pastinho-de-inverno
  • Canada: paturim annuel
  • Chile: hierba de la perdiz; pasto de la perdiz; pasto de las liendres; piagillo
  • Colombia: pasto azul; pata de gallina; piojillo
  • Germany: einjæhriges rispe; Einjæhriges Rispengras
  • India: ghass
  • Italy: fienarola annuale; gramigna delle vie
  • Japan: suzumenokatabira
  • Mexico: pastillo de invierno; zacate poa
  • Netherlands: straatgras; tuintjesgras
  • Poland: wiechlina roczna
  • South Africa: eenjarige blougras
  • Spain: cebadilla
  • Sweden: vitgroee
  • Tanzania: winter grass
  • Turkey: salkim otu
  • UK: annual meadowgrass; annual poa
  • Uruguay: pasto de invierno; pelo de rata
  • Yugoslavia (Serbia and Montenegro): enoletna latovka; jednogodisjna livadarka; vlasnjaca

EPPO code

  • POAAN (Poa annua)

Summary of Invasiveness

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P. annua is a cosmopolitan grass included in the Global Compendium of Weeds (Randall, 2012) and listed as one of the most aggressive weeds invading areas from sea level up to 1200 m in elevation. It can be found from Arctic to the Antarctic regions in practically all terrestrial ecosystems (Holm et al., 1997; USDA-ARS, 2014). It is listed as a weed in 38 crops in more than 80 countries within and outside its native distribution range. It grows in a wide variety of soils, tolerates trampling, mowing, and frozen conditions, and is a frequent weed in areas heavily trafficked by livestock or humans. This species has the potential to outcompete other plants and crops (Holm et al., 1997). 

Taxonomic Tree

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

Notes on Taxonomy and Nomenclature

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The name Poa annua is universally accepted for this common and widespread weed. It is tetraploid (2n=28), and it has been suggested that it is an allotetraploid hybrid between the two diploid species, Poa infirma and Poa supina (Nannfeld, 1937; Tutin 1952). More recently Darmency and Gasquez (1997) showed that spontaneous hybrids were easy to obtain when these species were grown in proximity. The two diploids are now confined to well-separated areas; P. infirma on the Mediterranean and Atlantic borders and P. supina to the mountains of central Europe. This is in striking contrast to the distribution of P. annua which is worldwide.

Description

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P. annua is an annual grass which may persist as a short-lived perennial. It is small in stature and may be variable in form. It is sometimes erect but, in the vegetative state, it is usually geniculate and may root at the nodes. Flowering culms are erect, usually 10-20 cm tall but occasionally taller.

The vegetative parts are completely hairless. The leaves are flat, slightly keeled with characteristic 'tramlines'. The leaves are smooth and abruptly contracted at the apices to give a characteristic 'boat-shaped tip'. A further characteristic is that the leaves are often transversely wrinkled. The leaves are folded in the sheath which is smooth and somewhat compressed. (Contrast this with Poa trivialis where the leaf sheaths and culms are typically rough). The ligule is membranous and typically 2-3 mm (but may be 1-5 mm).

The culms are smooth, bearing open triangular or ovate panicles, 2 - 8 cm long (occasionally up to 12 cm) and composed of solitary or paired branches. The spikelets are 3 - 5 mm long, lanceolate with 3 - 5 florets. The glumes are boat shaped with an acute apex; the lower 1.5 - 3 mm long with 1 vein and the upper 2 - 4 mm long with 3 veins. The lemmas are ovate, 5-veined, 2.5 - 4 mm long with a keel, and may have hairs along the veins. There are no awns. The anthers are 0.6 - 1 mm long and 2 - 4 times as long as they are broad.

Distribution

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P. annua is native to temperate areas of Eurasia. The list of countries in which this species now occurs may not be complete, as P. annua has spread to almost all areas of the world where temperate and subtropical crops are grown, and to some relatively undisturbed habitats. It is the only non-native flowering plant species which has successfully established a breeding population in the maritime Antarctic and has been shown to maintain a seed bank (Wódkiewicz et al., 2014), and has become widespread throughout the sub-Antarctic since its introduction (Williams et al., 2013). It is still being recorded from new locations, for example being found on the forefield of a retreating glacier on King George Island, Antarctica (Olech et al., 2011), and in Venezuelan Guyana for the first time in 2010 (Delascio Chitty and Nozwa, 2010). Cody et al. (2000) reported it as a new record for the mainland Northwest Territories, Canada, after discovering it along an oil pipeline.

Risk of Introduction

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P. annua and P. trivialis are common contaminants of grass seed crops (Rowarth et al., 1990) and can be extremely difficult to separate from the desired species. P. annua has annual and perennial types and individual plants can produce large number of seeds (1050-2250 seeds/plant) increasing the risk of introduction into new areas (Holm et al., 1997). 

Habitat

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P. annua is common on a range of agricultural soils and in grassland from lowland to mountain pastures (up to 1213 m in the UK but to much higher altitudes in tropical regions). It is tolerant of a range of soil conditions and of moderate to hard frost, however, it prefers fertile agricultural soils with an adequate water supply. The characteristics of rapid flowering and profuse seeding enable the plant to survive adverse conditions by exploiting a short-lived niche. P. annua is also a common weed in garden, lawns, pastures, golf courses, urban parks, margins of streams and lakes, roadsides, and disturbed sites in coastal forests, mesic forests, and wet forests (Holm et al., 1997; Wagner et al., 1999). 

Habitat List

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

Hosts/Species Affected

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The list of host crops provided reflects those which are most commonly infested with P. annua, and is by no means exhaustive. Whilst most prominent in crops which offer relatively little competition for all or part of the year, P. annua is a potential weed in almost all temperate crops. Notable examples are vegetable crops sown in wide rows and other crops, for example, maize and sugar beet where the crop foliar canopy develops late in the season or is not sustained throughout the growing season. In grassland, it can persist as an annual or short lived perennial in newly established grass swards or where the sward is subject to intensive pressure from trampling, cutting or soil disturbance (in gateways and on golf courses). In New Zealand, it appears to alternate in Waikato dairy pastures with a very different grass, Digitaria sanguinalis. D. sanguinalis is a summer grass whereas P. annua occurs in the same areas as a winter grass (Wardle et al., 1994).

Biology and Ecology

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Genetics

The chromosome number reported for P. annua is 2n = 28 (Holm et al., 1997).

Reproductive Biology

P. annua is a wind-pollinated species. Plants are normally self-pollinated with 0 to 15% outcrossing in natural populations and seeds are viable in only 1 to 2 days after pollination (Holm et al., 1997).

Physiology and Phenology

P. annua is day neutral and flowering begins in early spring in the northern hemisphere. Seed production peaks in May and June and continues at a lower level thereafter. Individuals that grow as annuals die after flowering (Holm et al., 1997).

Longevity

P. annua is a fast-growing species with annual and perennial types (Holm et al., 1997). 

Growth and Population Dynamics

In general, P. annua can be said to be a weakly competitive weed which has been highly successful in occupying niches which allow it to avoid competition with dominant plants. The seed is relatively short-lived (Lawson et al., 1993, suggest 99% decline is reached in 4 to 6 years), but is often moderately dormant and forms a significant presence in the seed bank in many agricultural soils. Holm et al. (1997) summarize a number of publications indicating that the seeds may have an initial dormancy, overcome variously by light, nitrate, chilling and, or, alternating temperatures. A high degree of phenotypic plasticity means that this species is able to develop specialized adaptations and growth forms depending on localized climatic, edaphic and biotic conditions. Standifer and Wilson (1988), comparing material from three different U.S. states illustrated adaptation to different climatic zones in the USA. Till-Bottraud et al. (1990) suggested adaptation to either irrigated or dry areas within California. Lin-Wu et al. (1987), also in California, suggested genetic differentiation among populations on golf courses due to the different management of greens, fairways and rough areas. This conclusion was broadly supported by work on Japanese golf courses (Itoh et al., 1996). The same authors suggest adaptation to the different habitats provided by paddy rice and upland fields (Itoh et al., 1995).

The adaptability of this species makes ecological generalizations difficult and often meaningless. It exhibits year-round germination if temperature and moisture status is suitable. In temperate regions (for example, lowland UK), it is rarely restricted by low temperature in winter, but frequently restricted by moisture availability in summer. Depending on habitat, climate and management P. annua may vary from a true ephemeral to a short-lived perennial. Annual types flower in all daylengths and mature in 3 to 4 months. Perennial types flower more abundantly in short days with cool temperatures (Holm et al., 1997).

Climate

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ClimateStatusDescriptionRemark
Af - Tropical rainforest climate Tolerated > 60mm precipitation per month
Am - Tropical monsoon climate Tolerated Tropical monsoon climate ( < 60mm precipitation driest month but > (100 - [total annual precipitation(mm}/25]))
As - Tropical savanna climate with dry summer Tolerated < 60mm precipitation driest month (in summer) and < (100 - [total annual precipitation{mm}/25])
Aw - Tropical wet and dry savanna climate Tolerated < 60mm precipitation driest month (in winter) and < (100 - [total annual precipitation{mm}/25])
BS - Steppe climate Tolerated > 430mm and < 860mm annual precipitation
BW - Desert climate Tolerated < 430mm annual precipitation
Cf - Warm temperate climate, wet all year Tolerated 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
Cw - Warm temperate climate with dry winter Preferred Warm temperate climate with dry winter (Warm average temp. > 10°C, Cold average temp. > 0°C, dry winters)
Df - Continental climate, wet all year Tolerated Continental climate, wet all year (Warm average temp. > 10°C, coldest month < 0°C, wet all year)
Ds - Continental climate with dry summer Tolerated Continental climate with dry summer (Warm average temp. > 10°C, coldest month < 0°C, dry summers)
Dw - Continental climate with dry winter Tolerated Continental climate with dry winter (Warm average temp. > 10°C, coldest month < 0°C, dry winters)
EF - Ice cap climate Tolerated Ice cap climate (Average temp. all months < 0°C)
ET - Tundra climate Tolerated Tundra climate (Average temp. of warmest month < 10°C and > 0°C)

Air Temperature

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Parameter Lower limit Upper limit
Mean annual temperature (ºC) 4.9 27.4
Mean minimum temperature of coldest month (ºC) -4

Rainfall

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ParameterLower limitUpper limitDescription
Mean annual rainfall90430mm; lower/upper limits

Soil Tolerances

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Soil drainage

  • free
  • impeded

Soil reaction

  • acid
  • alkaline
  • neutral

Soil texture

  • heavy
  • light
  • medium

Notes on Natural Enemies

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A plant with such a widespread distribution may be expected to have a range of pests and parasites. This does indeed appear to be the case.

The numerous pests do not appear to detract from the general success of the species, although some are occasionally serious in situations where P. annua is a desired component, for example, of golf greens. The coleopteran, Listronotus maculicollis has been reported as a cause of damage on golf courses in New York, USA (Vittum and Tashiro, 1987) and the scarabaeid, Phyllopertha horticola was found to be very patchily distributed on a golf tee in Berkshire, UK by Gange et al. (1991). Crutchfield and Potter (1995) studied the importance of scarabaeidae on Poa pratensis but found that survival of larvae of Popillia japonica and Cyclocephala lurida was as high or higher on P. annua.

Fungal diseases have also been studied for this species, both as a cause of disease and as potential biological control agents. Landschoot (1996) isolated Leptosphaeria korrae from circular patches of chlorotic plants on three golf courses in Pennsylvania, USA. Hsiang et al. (1995) concluded that Pythium species were a cause of cool-season die back of golf course turfgrass in Ontario and Quebec, Canada. In India, Singh and Bedi (1991) reported infestation of P. annua with a powdery mildew, Sclerophthora macrospora. Sclerotinia homoeocarpa was isolated from tissue affected with 'dollar spot' in western Washington, USA by Stahnke and Foss (1994)

The bacterium Xanthomonas campestris has been shown to be an effective pathogen of P. annua (Imaizumi et al., 1997), although inconsistent results have been observed by McCarty and Tucker (2005) due to the microbe’s sensitivity to environmental changes.

Means of Movement and Dispersal

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P. annua spreads by seeds. Individual plants can produce between 1050 and 2250 seeds/plant. Seeds can be dispersed by wind, water or attached to animal fur, livestock and vehicles. Seeds may also be spread as a contaminant in grass and crop seeds and in soils (Holm et al., 1997). 

Pathway Causes

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CauseNotesLong DistanceLocalReferences
Animal productionSeed adhered to livestock Yes Yes Holm et al., 1997
Crop production Yes Yes Holm et al., 1997
Disturbance Yes Yes Holm et al., 1997
Escape from confinement or garden escapeWeed in gardens, yards and parks Yes Yes Holm et al., 1997
ForageWeed in pastures Yes Yes Holm et al., 1997
Garden waste disposal Yes Yes Holm et al., 1997

Pathway Vectors

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VectorNotesLong DistanceLocalReferences
Clothing, footwear and possessionsSeeds can be dispersed adhered to clothes Yes Yes Holm et al., 1997
Debris and waste associated with human activitiesWeed in gardens , yards, parks , agriculture and pasturelands Yes Yes Holm et al., 1997
Land vehiclesSeed Yes Yes Holm et al., 1997
LivestockSeeds can be dispersed adhered to livestock Yes Yes Holm et al., 1997
Machinery and equipmentSeed Yes Yes Holm et al., 1997
Soil, sand and gravelSeed Yes Yes Holm et al., 1997
WaterSeed Yes Yes Holm et al., 1997
WindSeed Yes Yes Holm et al., 1997

Impact Summary

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CategoryImpact
Cultural/amenity Negative
Economic/livelihood Positive and negative
Environment (generally) Negative

Economic Impact

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Holm et al. (1997) indicate that P. annua is a weed of 38 crops in 80 countries and is most frequently reported as a weed of vegetables, cereals, turf, sugarbeet, potatoes and orchards.

P. annua has frequently been listed as one of the major weed species in a wide range of crops and regions of which a few examples follow: sports turf in the UK (Raikes et al., 1994); vegetable crops in New South Wales, Australia (Greenhalgh and Michael, 1989) and vines and soft fruit in the European Union (Clay, 1987). It is among the most important monocotyledonous weeds in Pakistan (Hussain and Rashid, 1989) and is common in oilseed rape in north-east Scotland (Whytock and Carnegie, 1990). It was one of the most frequent weeds in a survey of orchards in Portugal (Sa et al., 1989).

On a plant-for-plant basis, P. annua is only weakly competitive. Woolley and Sherrott (1993) reported that an economic response to control in winter wheat was only obtained when populations exceeded 714 plants/m² in the drier regions of the UK and 416 plants/m² in the wetter climate of South Wales. Lutman et al. (1995) produced a tentative index of the competitive abilities of eleven weed species in autumn-sown oilseed rape and placed P. annua low in the list.

Despite a relatively low competitive ability, this plant is a significant weed in many crops. Populations may build up to very high levels and, at such levels, an economic response is obtained and the soil seed bank may become very high. In such densely infested land, any gap in the crop will rapidly be colonized and completely occupied by P. annua, thus causing difficulties in crop harvest and management. In weakly competitive crops, or crops where the weed is able to establish a foliar canopy significantly before the crop, the situation is much more serious.

P. annua is believed to play an important part in the transmission of barley yellow dwarf luteovirus between successive crops of wheat and barley by acting as an alternate host to the virus and to its principal vectors; the cereal aphids, Sitobion avenae, Rhopalosiphum padi and Metopolophium dirhodum (Masterman et al., 1994; Kendall et al., 1996). An analogous situation occurs with the transmission of maize rough dwarf fijivirus by the cicadellid Laodelphax striatella for which P. annua is an alternate host (Grancini 1988). It has also been observed that P. annua supports high numbers of larvae of the Argentine stem weevil, Listronotus bonariensis, which is a pest of tall fescue in dairy pastures in New Zealand (Prestidge et al., 1989).

Threatened Species

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Threatened SpeciesConservation StatusWhere ThreatenedMechanismReferencesNotes
Gratiola amphiantha (little amphianthus)NatureServe NatureServe; USA ESA listing as threatened species USA ESA listing as threatened speciesAlabama; Georgia; South CarolinaCompetition - monopolizing resourcesUS Fish and Wildlife Service, 1993

Risk and Impact Factors

Top of page Invasiveness
  • Invasive in its native range
  • Proved invasive outside its native range
  • Has a broad native range
  • Abundant in its native range
  • Highly adaptable to different environments
  • Is a habitat generalist
  • Tolerates, or benefits from, cultivation, browsing pressure, mutilation, fire etc
  • Pioneering in disturbed areas
  • Highly mobile locally
  • Benefits from human association (i.e. it is a human commensal)
  • Fast growing
  • Has high reproductive potential
Impact outcomes
  • Altered trophic level
  • Damaged ecosystem services
  • Ecosystem change/ habitat alteration
  • Modification of hydrology
  • Modification of nutrient regime
  • Modification of successional patterns
  • Monoculture formation
  • Negatively impacts agriculture
  • Reduced amenity values
  • Reduced native biodiversity
  • Threat to/ loss of native species
Impact mechanisms
  • Competition - monopolizing resources
  • Competition - smothering
  • Pest and disease transmission
  • Hybridization
  • Rapid growth
Likelihood of entry/control
  • Highly likely to be transported internationally accidentally
  • Difficult to identify/detect as a commodity contaminant
  • Difficult to identify/detect in the field
  • Difficult/costly to control

Uses

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P. annua cannot be said to have any real use in productive agriculture although it may provide some forage in very poor grassland. In ornamental and sports turf the situation is more complex. It is often regarded as a weed, supplanting more desirable species but, in some swards, it provides the only effective green cover. It is frequently the dominant species on golf tees and greens, and varieties have been bred for this purpose in the USA.

Uses List

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Animal feed, fodder, forage

  • Forage

Environmental

  • Host of pest

General

  • Ornamental

Similarities to Other Species/Conditions

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Poa infirma is also small in stature but is erect in habit, always annual and rarely a weed. It is native to sandy coastal soils in the extreme south west of the UK, south-western Europe, North Africa and Asia. The spikelet is more linear with 5 - 6 distant or only slightly overlapping florets. Unopened anthers are 0.2 - 0.5 mm long and about as long as broad.

In contrast, P. trivialis is usually an agricultural weed in arable crops and productive grassland. It may be confused at a very early seedling stage but is easily distinguished at maturity. It is a much larger grass with culms up to 90 cm tall. It is perennial but succeeds as an autumn germinating annual in winter cereal crops. Leaves taper more gradually to the tip and ligules are up to 10 mm long with an acute point. Leaf sheaths and culms are usually rough. Panicles are larger and spikelets more compressed. P. trivialis is diploid (2n=14).

Prevention and Control

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Cultural Control

Cultural control is by ploughing to achieve inversion of the soil. Many seeds will survive to create a problem when the soil is re-inverted, but the limited seed life of this and other small seeded grasses still makes this an effective measure. Hoeing and harrowing may be very effective in suitable conditions but P. annua is one of the more resistant plants because of its ability to develop adventitious roots in damp conditions.

Chemical Control

Chemical control of P. annua has been studied comprehensively, and no less than 26 active ingredients are recommended for its control in the UK, some alone and some used in mixtures which are listed below. Two general caveats must, however, be mentioned;

1. P. annua, in contrast to many other grass weeds, including P. trivialis, has an innate ability to resist herbicides of the aryloxy phenoxy propionate (for example, fluazifop-butyl) and cyclohexanedione groups (for example, sethoxydim). This is caused by an insensitive form of the acetyl-coenzyme A carboxylase (ACCase) enzyme which is the target of these chemicals (Herbert et al., 1996, 1997).

2. In addition to the innate resistance described above, some populations of P. annua have evolved resistance to herbicides which are normally effective. Most commonly, resistance has evolved to the triazine herbicides (Barros and Dyer, 1988; Cavalloro 1989) in situations where triazines are used frequently - maize fields, orchards, nurseries, vineyards and uncropped areas such as railways. Clay (1989) has described a case of evolution of co-resistance to simazine and paraquat where hops had been treated with these two chemicals for about 25 years.

The following list of recommended herbicides is compiled from the UK Pesticide Guide, 1998 (Whitehead, 1998). It has wider utility, but includes only herbicides approved under the UK Control of Pesticides Regulations 1986. Thus, chemicals for which the manufacturer makes no label claim are not included. Some further herbicide recommendations can be found in Mamarot and Rodriguez (1997).

Herbicides recommended in beet crops are chloridazon, ethofumesate, lenacil, metamitron and tri-allate; in beans (Vicia faba) they are simazine, cyanazine + pendimethalin, pendimethalin + prometryne, terbutryne + trietazine and tri-allate; in Phaseolus beans they are fomasafen and monolinuron + paraquat; in cereals they are isoproturon, linuron + trifluralin, methabenzthiazuron, terbutryne, tri-allate, cyanazine + terbuthylazine and diflufenican + terbuthylazine; in oilseed rape they are carbetamide, metazachlor and tri-allate; in grass leys they are ethofumesate + bromoxynil + ioxynil; in peas they are cyanazine + pendimethalin, pendimethalin + prometryne and terbutryne + trietazine and in onions and leeks they are chloridazon, monolinuron and tri-allate.

Many of the same herbicides are recommended for control of P. trivialis, but for this species there is the additional option of diclofop-methyl in most broad-leaved crops, and clodinafop or fenoxaprop-ethyl in cereals.

Preemergent herbicides such as benefin, bensulide, dithiopyr, oryzalin, oxadiazon, pendimethalin, and prodiamine and their combinations such as benefin/oryzalin have been found effective for limiting germination of P. annua in turf in the USA. They should be applied a few weeks before weed seeds germinate to be most effective, as they have no effect on emerged plants. There are a few relatively new postemergent herbicides that control P. annua, but none of them can be used in all turf species. Foramsulfuron, sulfosulfuron, and trifloxysulfuron, for example, can be used only on warm-season turfgrass species. In ornamental crops, clethodim is listed by the University of California as the only postemergent herbicide for broadleaved ornamentals which has an effect on P. annua.

Intensive herbicide use in turf has led to reports of resistance to an increasing number of herbicides. Brosnan et al. (2012) reported a glyphosate-resistant biotype of P. annua in Tennessee. In 2001, Lowe et al. reported dinitroaniline-resistant P. annua. Acetolactate synthase (ALS)-inhibiting herbicides such as trifloxysulfuron, foramsulfuron, and bispyribac-sodium have been effective for P. annua control in turfgass, but resistant biotypes have been reported on golf courses in South Carolina and Georgia, USA (Cross et al., 2013). Brosnan et al. (2014) report the development of resistance to prodiamine in Tennessee, and suggest indaziflam for control of resistant populations.

Biological Control

McCarty et al. (2005) report on trials for using the bacterium Xanthomonas campestris to control P. annua, but say that inconsistent results have been observed due to the pathogenic microbe's extreme sensitivity to changes in their environments. Use of arbuscular mycorrhizas to slowly reduce the abundance of P. annua and increase the growth of desirable perennial grasses in sports turf is discussed by Gange and Whitfield (2004) and Bary et al. (2005).

References

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Contributors

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22/04/14 Updated by:

Julissa Rojas-Sandoval, Department of Botany-Smithsonian NMNH, Washington DC, USA

Pedro Acevedo-Rodríguez, Department of Botany-Smithsonian NMNH, Washington DC, USA