Poa pratensis
(smooth meadow-grass)

Pictures

Picture	Title	Caption	Copyright
Title Inflorescence Caption Poa pratensis (smooth-stalked meadowgrass, Kentucky bluegrass); inflorescence. Guilford Co., Greensboro, North Carolina, USA. May, 2011. Copyright Public Domain - Original image by Doug Goldman/USDA-NRCS-NPDT	Inflorescence	Poa pratensis (smooth-stalked meadowgrass, Kentucky bluegrass); inflorescence. Guilford Co., Greensboro, North Carolina, USA. May, 2011.	Public Domain - Original image by Doug Goldman/USDA-NRCS-NPDT
Title Close-up of inflorescence Caption Poa pratensis (smooth-stalked meadowgrass, Kentucky bluegrass); close-up of inflorescence. Guilford Co., Greensboro, North Carolina, USA. May, 2011. Copyright Public Domain - Original image by Doug Goldman/USDA-NRCS-NPDT	Close-up of inflorescence	Poa pratensis (smooth-stalked meadowgrass, Kentucky bluegrass); close-up of inflorescence. Guilford Co., Greensboro, North Carolina, USA. May, 2011.	Public Domain - Original image by Doug Goldman/USDA-NRCS-NPDT
Title Ligule Caption Poa pratensis (smooth-stalked meadowgrass, Kentucky bluegrass); ligule. Guilford Co., Greensboro, North Carolina, USA. May, 2011. Copyright Public Domain - Original image by Doug Goldman/USDA-NRCS-NPDT	Ligule	Poa pratensis (smooth-stalked meadowgrass, Kentucky bluegrass); ligule. Guilford Co., Greensboro, North Carolina, USA. May, 2011.	Public Domain - Original image by Doug Goldman/USDA-NRCS-NPDT
Title Close-up of ligule Caption Poa pratensis (smooth-stalked meadowgrass, Kentucky bluegrass); close-up of ligule. Guilford Co., Greensboro, North Carolina, USA. May, 2011. Copyright Public Domain - Original image by Doug Goldman/USDA-NRCS-NPDT	Close-up of ligule	Poa pratensis (smooth-stalked meadowgrass, Kentucky bluegrass); close-up of ligule. Guilford Co., Greensboro, North Carolina, USA. May, 2011.	Public Domain - Original image by Doug Goldman/USDA-NRCS-NPDT
Title Close-up of node Caption Poa pratensis (smooth-stalked meadowgrass, Kentucky bluegrass); close-up of node. Guilford Co., Greensboro, North Carolina, USA. May, 2011. Copyright Public Domain - Original image by Doug Goldman/USDA-NRCS-NPDT	Close-up of node	Poa pratensis (smooth-stalked meadowgrass, Kentucky bluegrass); close-up of node. Guilford Co., Greensboro, North Carolina, USA. May, 2011.	Public Domain - Original image by Doug Goldman/USDA-NRCS-NPDT
Title Seeds Caption Poa pratensis (smooth-stalked meadowgrass, Kentucky bluegrass); close-up of seeds. Copyright Public Domain - Steve Hurst/USDA-NRCS PLANTS Database	Seeds	Poa pratensis (smooth-stalked meadowgrass, Kentucky bluegrass); close-up of seeds.	Public Domain - Steve Hurst/USDA-NRCS PLANTS Database

Identity

Preferred Scientific Name

• Poa pratensis L.

Preferred Common Name

• smooth meadow-grass

Variety

• Poa sergievskajae

Other Scientific Names

• Poa montana Honck.
• Poa nymannii Tineo
• Poa oligeria Steud.
• Poa pachyantha Keng f. ex S.L.Chen
• Poa paratunkensis Kom.
• Poa peckii Chase
• Poa pinegensis Roshev.
• Poa pratensis subsp. latifolia (Weihe ex Mert. & W.D.J. Koch) Schübl. & G. Martens
• Poa pratensis subsp. sabulosa (Roshev.) Tzvelev
• Poa pratensis subsp. sergievskajae (Prob.) Tzvelev
• Poa pratensis subsp. skrjabinii Tzvelev
• Poa pratensis subsp. sobolevskiana (Gudoschn.) Tzvelev
• Poa pratensis subsp. turfosa (Litv.) Vorosch.
• Poa pratensis subsp. zhukoviae Yurtsev & Tzvelev
• Poa pratensis var. hatusimae (Ohwi) Ohwi
• Poa pratensis var. majdelii (Roshev.) Bondar ex Korovina
• Poa pratensis var. rigens (Hartm.) Laest.
• Poa pratensis var. sabulosa Roshev.
• Poa pratensis var. stricta Hook.
• Poa pratensis var. subglabriflora (Roshev.) Bondarenko ex Korovina
• Poa pratensis var. transnominata Bondarenko ex Korovina
• Poa pratensis var. transnominatum Bondar ex Korovina
• Poa pratensis var. turfosa (Litv.) Bondarenko ex Korovina
• Poa pratensis var. umbrosa Parn.
• Poa pratensis var. urjanchaica (Roshev.) Bondarenko ex Korovina
• Poa pseudopratensis Beyer
• Poa rigens Hartm.
• Poa sobolevskiana Gudoschn.
• Poa stenachyra Keng ex Keng f. & G.Q.Song
• Poa subcaerulea var. anceps (Gaudich.) Soó
• Poa subglabriflora Roshev.
• Poa todarii Lojac.
• Poa turfosa Litv.
• Poa urjanchaica Roshev.

International Common Names

• English: bird grass; blue grass; common meadow-grass; English grass; green grass; June grass; Kentucky bluegrass; narrow-leaf meadow grass; northern meadow grass; smoothstalk bluegrass; smooth-stalked meadow grass; spreading bluegrass
• Spanish: grama de prados; poa cmun; poa de los prados; zacate poa
• French: pâturin des prés
• Portuguese: capim-do-campo; erva-de-febra

Local Common Names

• Germany: schmalblättriges Rispengras; Wiesen- Rispengras; Wiesenrispengras
• Italy: fienarola dei prati; gramigna dei prati
• Japan: Nagahagusa
• Netherlands: gewoon beemdgras
• Sweden: Aengsgroee

EPPO code

• POAPR (Poa pratensis)

Summary of Invasiveness

P. pratensis is a perennial, cool season mat-forming grass. It is native to Europe and Asia and has probably been introduced to the USA and Canada, where it is invasive in the northern prairie states, as well as in New Zealand, Indian Ocean islands and South Africa. The wide, creeping rootstock produces underground runners and leafy shoots. In the USA, where it is known as Kentucky bluegrass, it is regarded as a crop in some systems but as a weed in others. It is highly valued as a pasture and turf grass, particularly in golf courses, but is considered an invasive weed in natural grassland ecosystems, where it outcompetes native species, reduces biodiversity and alters nitrogen cycling and ecosystem function. It is defined as ‘high risk’ for the Pacific region and invasive in Hawaii by PIER (2016).

Taxonomic Tree

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

Notes on Taxonomy and Nomenclature

Description

P. pratensis is a herbaceous perennial grass species with shallow creeping rhizomes. It grows from 10 to 90 cm in height. The leaves have boat-shaped tips, narrowly linear, up to 20 cm long and 3-5 mm broad, smooth or slightly roughened, with a rounded to truncate ligule 1-2 mm long. The broad, blunt leaves spread at the base, forming close mats. The conical panicle is 5-20 cm long, with 3 to 5 branches in the basal whorls; the oval spikelets are 3-6 mm long with 2 to 5 florets, and are purplish-green or grey. Seeds tightly enclosed in the lemma and palea, 2mm long.

Distribution

P. pratensis is certainly native to Europe and Asia and probably some countries of northern Africa. It has been introduced to Mexico, South America, southern Africa, Atlantic islands, Antarctica, Australia, New Zealand and Pacific islands including Hawaii.

Its status in North America is not completely clear, with some authorities suggesting it is native across most of USA and Canada (Fernald, 1950; Canadensys, 2016) while others believe it is exotic (Hitchcock, 1950; ISSG, 2016). BONAP (2016) and USDA-NRCS (2016) take an intermediate view, suggesting that some forms of the plant may be native, at least in the northern states of the USA and Canada, while others (presumably those of commercial interest) have been introduced. Overall, it seems most probable that it is effectively introduced across North America. In any case it is most common in the north and much less common in southern states. Most introductions have been deliberate, for cultivation. In some cases it may continue to be restricted to cultivation, and not naturalised, but it has not been possible to make this distinction in the Table below.

Distribution Table

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.

History of Introduction and Spread

According to Cook (2015), P. pratensis arrived in the USA from Europe during colonial times (1600s) and rapidly spread west along with European settlers. It performed well in north central Kentucky for forage, which led to the common name Kentucky bluegrass. It continued to spread both west and north until it became an important grass throughout northern USA and Canada from coast to coast. P. pratensis was introduced to Hawaii in 1879 (Wilcox, 1015) and to the Antarctic in 1954 (Pertierra et al., 2013). Earliest dates of collection according to GBIF (2016) include 1900 for South Africa, 1828 for New Zealand, 1848 for Australia, 1850 in Chile and 1893 in Mexico.

Habitat

P. pratensis is widespread throughout the UK and north-eastern USA in plant assemblages of pasture and arable land, roadsides, waste-ground, forest edges, dry hills, marshes, along seashores and walls. P. pratensis is used for hay, grazing and for park and sportsground turf (Clarke and Malte, 1913; Phillips, 1980).

Habitat List

Hosts/Species Affected

P. pratensis has been reported to impact on, Triticum aestivum, Hordeum vulgare and Anemone patens.

Biology and Ecology

Genetics

P. pratensis is very variable genetically, with chromosome numbers ranging from 2n=14 to 154, but the most common numbers are 2n = 28 or 56 (Missouri Botanic Garden, 2016). The genetic variability in P. pratensis has been studied by Raggi et al. (2015) where they found relatively little consistent variation between cultivated and wild types, but variation according to region of collection. The most distinct variation is shown by populations from China and Mongolia and it is suggested that this is a likely area of origin of the species.

Reproductive Biology

P. pratensis may hybridize but some forms produce seed apomictically, whereby the seed forms from cells contained within the ovary wall of the flowers (the progeny are identical to the parent plant) (Hubbard, 1959). Breeders have been able to make controlled crosses and in many cases the resulting crosses are still highly apomictic. Many early cultivars, including ‘Merion’, are simple selections of highly apomictic plants.

Physiology and Phenology

Seeds of P. pratensis germinate in autumn after a chilling period. In a study by Aamlid and Arntsen (1997), the optimum constant temperature for germination was 16°C but higher rates of germination were obtained under fluctuating temperatures. Light was beneficial at constant temperatures, but had no benefit, or was even inhibitory at alternating temperatures. Germination is delayed under dry soil conditions, more so than in related Poa species (Springer and Goldman, 2016). Seedlings establish forming a short tuft, rhizomes and tillers (North Dakota Department of Agriculture, 2005). It may take up to three years for plants to establish fully from seed but is then very long-lived.

Valuable detail on the phenology and ecology of P. pratensis are provided by Sather (2016). He records that the growth of each aerial shoot or underground rhizome is indeterminate until its shoot apex is triggered by environmental stimuli to initiate floral development. Each tiller or rhizome produces a single terminal aerial flowering stem. Floral initiation is induced by a period of vernalisation involving both an inductive developmental stage and a photoperiodic requirement before the inflorescence is initiated. Vernalisation is not transferred from one shoot to another, with the consequence that aerial shoots from either tillers or rhizomes formed in any given year (whether spring or fall) must overwinter before they will bloom. This requirement applies even though apical dominance is removed by removing the flowering culm. Flowering in the UK occurs from May to early July (Phillips, 1980). Each panicle (flower) is capable of producing between 100 and 200 seeds. Seeds can remain viable for up to two years.

Environmental Requirements

P. pratensis is best adapted to well-drained, fertile, medium-textured soils of limestone origin, although it can survive on poorly-drained and heavy textured soils. It prefers soils of pH 6.0 to 7.5. Optimum temperatures for growth are between 15 to 32°C and it grows best in humid areas. It prefers high sunlight but can do well in light shade if moisture and nutrients are sufficient. It is usually dormant during dry or hot weather but can survive severe droughts (ISSG, 2016). Frost is tolerated but tolerance is reduced under increased nitrogen availability (Malyshev and Henry, 2012).

Climate

Air Temperature

Natural enemies

Notes on Natural Enemies

P. pratensis is affected by a very wide range of fungal and nematode enemies, but none are known to be very widespread or damaging. Of greatest economic significance perhaps are those which affect P. pratensis on golf courses and other amenities.

Among many insects P. pratensis is eaten by the caterpillars of the meadow brown (Maniola jurtina) and gatekeeper (Pyronia tithonus) butterflies. Adults of the common sun beetle (Amara aenea) feed on the developing seeds. The leafhopper Eupelix cuspidata and the grassbug Myrmus miriformis feed on young blades and developing seeds.

Impact Summary

Economic Impact

In the UK and China, P. pratensis has been reported as a weed in agricultural crops such as wheat and other cereal crops (Yann and QinHua, 2009; Bayer, 2016).

Environmental Impact

In a recent review, DeKeyser et al., (2015) comment that P. pratensis has become the most-common species on the untilled, native prairie sites of much of North and South Dakota, one of the most endangered ecosystems in North America. Toledo et al., (2014) found that invasion of the prairies in northern USA may bring negative consequences to ecosystem services, such as pollination, habitat for wildlife species and alteration of nutrient and hydrologic cycles, among others. All these impacts can negatively affect livestock production as well as wildlife habitat and ecosystem services (Hendrickson and Lund, 2010). In addition to this, P. pratensis can outcompete native plant species and therefore reduce biodiversity in invaded areas (North Dakota Department of Agriculture, 2005). The vital rates and population growth rate of a native US species, Anemone patens, was observed to be greatly reduced when growing with P. pratensis and other invasive grasses (Williams and Crone, 2006).

Litter produced by P. pratensis has been observed to form thick mats of ‘slicks’ on the soil surface (Hendrickson and Lund, 2010). The litter is known to inhibit seedling establishment of other plant species (Bosy and Reader, 1995).

P. pratensis is also a host of Aspergillus versicolor, a fungus which produces a mycotoxin causing mycotoxicosis in livestock (Rekha et al., 2016).

Despite being a non-native grass species in the USA, P. pratensis provides important habitat and oviposition sites for the rare grass skipper Polites mardon (Beyer and Schultz, 2010).

Social Impact

P. pratensis is an important plant of sports turf, especially on golf courses, parks and private gardens.

Risk and Impact Factors

• 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
• Tolerant of shade
• Highly mobile locally
• Benefits from human association (i.e. it is a human commensal)
• Long lived
• Fast growing
• Has high reproductive potential
• Has propagules that can remain viable for more than one year
• Reproduces asexually
• Has high genetic variability

• Ecosystem change/ habitat alteration
• Modification of fire regime
• Modification of hydrology
• Modification of nutrient regime

• Highly likely to be transported internationally accidentally
• Highly likely to be transported internationally deliberately
• Difficult to identify/detect as a commodity contaminant

Uses

Economic value

The main use of P. pratensis is for sports turf, especially for golf courses. It is also used in private gardens and parks and in ball fields and other heavy use areas such as picnic areas, as it thrives from mowing (USDA, 2002).

Environmental Services

P. pratensis and its seeds can be an important component in the diets of elk, mule deer, and bighorn sheep, numerous species of small mammals, songbirds, cottontail rabbit, wild turkey and prairie chickens. In P. pratensis-dominated grasslands there can be an abundance of small mammals which provide food for foraging raptors (USDA Forest Service, 2015)

P. pratensis is highly palatable to horses, cattle and sheep. It produces relatively low yields compared to other pasture grasses, but can be very productive in northeast USA on closely grazed intensive rotational grazing systems (USDA, 2002).

Despite being a non-native grass species in the USA, P. pratensis provides important habitat and oviposition sites for the rare grass skipper Polites mardon (Beyer and Schultz, 2010).

P. pratensis is also an excellent erosion control plant due to its dense, vigorous turf forming habit. It can be used as a mix with legumes or other grasses for erosion control in conservation cover, waterways, field borders, heavy use areas and critical areas such as steep banks and pond edges. It is also used alone or in seed mixtures as permanent cover for tree plantings and orchards (USDA, 2002).

Similarities to Other Species/Conditions

P. pratensis is similar in appearance to a number of closely related species in the same genus. P. pratensis flowers from May to July, as opposed to P. annua, which is in flower for eight months of the year. P. pratensis has a fairly prominent mid-vein in the middle of the blade. The ligule of P. pratensis is extremely short and square-ended, in contrast to P. annua and P. trivialis, in which it is silvery and pointed. P. pratensis is a dark green compared to the apple green colour of P. annua and P. trivialis.P. angustifolia may also be confused with P. pratensis; it differs mainly in narrower, stiffer leaves, but in any case is regarded by some authorities as a subspecies of P. pratensis. P. compressa, often occurring with P. pratensis in Europe and in the USA, is distinct in having flattened stems.

Prevention and Control

Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.

Physical/Mechanical Control

Mowing and raking are generally ineffective against P. pratensis and can actually stimulate rhizome and tiller production. Williams and Crone (2006) found that mowing and raking decreased Bromus inermis (smooth brome), a similar invasive grass, but increased P. pratensis. Common varieties of P. pratensis however, perform well when lightly grazed or mowed at 5 cm or higher, actually improving the stand. However, when intensively grazed, or mown below 5 cm, diseases can then develop which generally destroy the stand. The dwarf or compact turf varieties require mowing below 2 cm; so mowing is therefore not recommended for control unless there is disease already present in the stand below cutting level (North Dakota Department of Agriculture, 2005; Hendrickson and Lund, 2010). For eradication complete turf removal down to 12-25 cm is recommended.

Sather (2016) comments that the most widely used management procedure for controlling P. pratensis in natural areas is the use of fire. In Kansas and Nebraska, USA three successive years of annual spring burning are considered sufficient for conversion of rangeland from P. pratensis to dominance by native warm season grasses. In the north it appears that much longer periods of annual burning are required. In central North Dakota, refuge managers suggest that even longer periods may be required and that P. pratensis may never be eliminated but only held in control by fire. The timing of the prescribed burn, moisture and site conditions are important factors that may influence the response of the plant to burning. It is also critical to consider native species composition of the area prior to burning. Burning usually needs to be repeated annually for several years (North Dakota Department of Agriculture, 2005). USDA Forestry Service (2015) makes detailed comments on the factors influencing the effectiveness of fire in control of P. pratensis.

Chemical Control

In the USA, glyphosate is effective in reducing infestations of P. pratensis (North Dakota Department of Agriculture, 2005). Imazapyr and sulfometuron methyl can also provide control. However, chemical control may not be the preferred method of control in some regions due to its effect on native species (North Dakota Department of Agriculture, 2005), as these chemicals will likely also affect the native species that are desired. Sather (2016) records that atrazine, DMPA (‘Zytron’), DCPA (‘Dacthal’) and trifluoralin at suitable doses can provide some selective suppression of P. pratensis in a pasture situation.

In field experiments performed in the UK, Clay et al. (2006) found P. pratensis to be moderately resistant to resistant to all graminicide herbicides tested. It was only moderately susceptible to the broad-acting glyphosate in spring and autumn. Resistance was greater with autumn-applied herbicides than with spring applications. Established plants were more resistant than young plants. Bayer (2016) recommend chlortoluron, isoproturon, diflufenican and flufenacet alone or in mixtures for control of Poa species including P. pratensis in winter wheat and barley

IPM

A study in North Dakota, USA, found that burning followed by the application of a herbicide (imazapic) was more effective at reducing P. pratensis than burning or using a herbicide alone. Burning removed the heavy thatch layer associated with P. pratensis, which may have improved herbicide effectiveness. However, this study also found that while burn/herbicide treatment decreased P. pratensis, it caused an increase in smooth brome (Bromus inermis) (Hendrickson and Lund, 2010).

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Contributors

24/06/16 Updated by:

Chris Parker, Consultant, Bristol, UK

22/06/15 Original text by:

Philip Roberts, CABI, UK

Distribution Maps