Poa pratensis is a perennial, cool season mat-forming grass. The wide, creeping rootstock produces underground runners and leafy shoots. Runners creep under the surface of the ground and produce upright leafy stems from their ends. The stems are from 15cm to 1m in height, and eventually develop into flower-bearing stems (Clarke & Malte, 1913). Seedhead panicles have an open-pyramid shape and produce numerous small seeds (Bush, 2002). Each branch of the panicle carries several spikelets which are bluish green to purple. Each spikelet has four to five flowers enclosed within two glumes of equal size (Clarke & Malte, 1913). Leaves are smooth, soft and measure 1/8 to ¼ inch wide and 6 to 12 inches long with keeled tips (Bush, 2002). Kentucky bluegrass can be distinguished from other grasses by its narrow leaf blade which is V-shaped in cross section and boat-shaped tip.

Four subspecies have been identified: Poa pratensis alpigena, P. pratensis colpodea, P. pratensis irrigata and P. pratensis pratensis (ITIS 2008). There are also numerous cultivars.

Poa pratensis becomes dormant in summer, but regains green colour in autumn. Growth starts in early spring with tiller buds developing into stems or rhizomes (Bush, 2002). It grows early in the season when most other species are still dormant, and can thus spread very quickly (Wisconsin Department of Natural Resources, 2004).

Kentucky blue grass has value as a pasture grass and hay. It is palatable and is of high fattening value, and provides excellent forage for early livestock grazing (North Dakota Department of Agriculture, 2005). It is also used for beautification of parks and home lawns, and as a turf that is useful for heavy use areas such as campgrounds, golf fairways, picnic areas and ball fields. It is also used in erosion control due to its dense, vigorous turf forming habit. This plant also provides food for elk, deer, rabbits and turkey. Its seeds are eaten by birds and rodents (Bush, 2002).\r\n

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

Kentucky bluegrass can grow in many habitat types including meadows, roadsides, forest edges, dry hills, marshes and along seashores (Clarke & Malte, 1913).

Kentucky bluegrass is a shallow-rooted, perennial grass that reproduces both vegetatively and via seed. Once established plants expand mainly through the formation and growth of rhizomes and tillers, which are responsible for the sod-forming capability of the plant (North Dakota Department of Agriculture, 2005).\r\n

Each panicle (flower) is capable of producing between 100 to 200 seeds that can remain viable for up to two years. Seeds germinate in autumn after a chilling period. Seedlings establish forming a short tuft, rhizomes and tillers (North Dakota Department of Agriculture, 2005).

Poa 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 15.5 to 32°C and it grows best in humid areas. It prefers high sunlight areas 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.

Seed contaminant.

Sod forming grasses such as Poa pratensis are known to have negative effects on native prairie species in the northern Great Plains of the United States (Larson & Larson, 2010 and references therein). It outcompetes native plant species and reduces biodiversity in invaded areas (North Dakota Department of Agriculture, 2005). For example the vital rates and population growth rate of a native grass, Anemone patens was greatly reduced when growing among P. pratensis and other invasive grasses (Williams & Crone, 2006).\r\n

Litter produced by Kentucky bluegrass forms thick mats of “slicks” on the soil surface (Hendrickson & Lund, 2010). Litter from Kentucky bluegrass is known to inhibit seedling establishment of other plant species (Bosy & Reader, 1995). \r\n\r\n\r\n

Kentucky bluegrass has been found to disrupt ecosystem function by altering nitrogen cycling and carbon storage, lowering plant diversity and shifting seasonal forage production. These impacts affect livestock production, wildlife habitat and ecosystem services (Hendrickson & Lund, 2010 and references therein).

Controlled areas should be closely monitored because seeds of Kentucky bluegrass can remain viable for two years and the plant can continue to spread by tillers and rhizomes.\r\n

Physical: Mowing and raking are generally ineffective against Kentucky bluegrass, and can actually stimulate rhizome and tiller production. Therefore mowing is not recommended (Hendrickson & Lund, 2010; North Dakota Deparment of Agriculture, 2005).\r\n

Burning: Burning of Kentucky bluegrass can have variable results. Some studies have found Kentucky bluegrass to be negatively affected by fire (Hendrickson & Lund, 2010 and references therein). 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 important to consider native species composition of the area and what species will replace Kentucky bluegrass. Burning usually needs to be repeated annually for several years (North Dakota Department of Agriculture, 2005)\r\n\r\n\r\n\r\n

Chemical: Glycophosphate is effective in reducing infestations of Poa pratensis (Wisconsin Department on Natural Resources, 2004; 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 the effect on native species (North Dakota Department of Agriculture, 2005).\r\n

In field experiments performed in the UK, Clay et al. (2006) found Poa pratensis to be moderately resistant to resistant to all graminicide herbicides tested. It was only moderately susceptible to susceptible to the broad-acting Glycophosphate in spring and autumn. Resistance was greater with autumn-applied herbicides than with spring applications. Established plants were more resistant than young plants.\r\n

Integrated Management: A study carried out in North Dakota, USA found that burning followed by herbicide (Imazapic) was more effective at reducing Kentucky bluegrass than burning or herbicide alone. Burning removed the heavy thatch layer associated with Kentucky blue grass which may have improved herbicide effectiveness. However this study also found that while burn/herbicide treatment decreased Kentucky bluegrass it caused an increase in smooth brome (Bromus inermis), a similar invasive grass species (Hendrickson & Lund, 2010), a patterns also found in a study by Williams and Crone (2006). Similarly mowing/raking which decreased smooth brome caused an increase in Kentucky bluegrass. Community composition was also important in determining the effectiveness of a control technique (Hendrickson & Lund, 2010). This study highlights the importance of considering other species, community composition and length of time since treatments were applied (Hendrickson & Lund, 2010).