Poa annua found on sub-Antarctic islands are frequently found with leaves and inflorescences coloured with a dark reddish-purple pigment (Walton 1975).
Establishment of new plants can occur at any time of the year, though it is less likely under dry conditions. This weed is usually an annual, dying once it has set seed. The typical life cycle in New Zealand is to establish in late autumn and to finish seeding and die off in spring once it starts getting too dry. Annual bluegrass may be found in lawns at any time of the year if summer irrigation is sufficient to allow it (Massey University 2008).
Annual bluegrass colonises disturbed habitats and is not generally found in natural communities. Typical habitats include open forests, streambanks, lawns, gardens, agricultural fields and roadsides (GOERP, 2009). It prefers sites sheltered from wind including depressions, building sites, dumps, earthworks and old caterpillar tracks (Olech, 1996). It may also colonise bare soil on new landslips and sites heavily grazed by rabbits, but it tends to be outcompeted by native species within several years on these sites if disturbance is not continued (Scott & Kirkpatrick, 2005). It may also be found around water, including springs, streams and lagoons and may colonise steep rocky moraines (glacial debris) and gravel flats (Scott & Kirkpatrick, 2005). \r\n
Poa annua tolerates a wide range of severe climatic conditions, making it a potentially invasive species for the Sub-Antarctic region. On one volcanic island in the region annual bluegrass was noted to occur on volcanic ash (ash has a low organic content and is both unstable and porous with a pH of about 6.8) (Longton, 1966). Poa annua is also noted to thrive on disturbed well trodden ground, for example, in and around gentoo penguin rookeries in the Falklands (Davies, 1939 in Moore & Sladen, 1966), and at sites of reindeer trampling and elephant seal wallowing (Pratt & Smith, 1982).
Seed densities are commonly 200 000 per square metre in infested lawns, which is equivalent to 20 seeds in every square centimetre (Massey University 2008). Seed production can occur even when the plant is mowed as low as 1mm (GOERP, 2009). Seeds can lie dormant and viable for up to six years. (GOERP, 2009).
Principal source:
Compiler: IUCN/SSC Invasive Species Specialist Group (ISSG) with support from the EU-funded South Atlantic Invasive Species project, coordinated by the Royal Society for the Protection of Birds (RSPB)
Updates with support from the Overseas Territories Environmental Programme (OTEP) project XOT603, a joint project with the Cayman Islands Government - Department of Environment
Review:
Publication date: 2010-08-23
Recommended citation: Global Invasive Species Database (2024) Species profile: Poa annua. Downloaded from http://www.iucngisd.org/gisd/species.php?sc=1418 on 07-10-2024.
P. annua is a major weed in golf courses, which are usually composed of creeping bentgrass (Agrostis stolonifer) and Kentucky bluegrass (Poa pratensis). Annual bluegrass reduces the aesthetics, functionality and quality of these grasses due to its lighter green colour, unsightly seedheads and shallow root system (Hart & McCullough, 2007). It also has poor disease, drought and wear tolerances that create unsightly patches in creeping bentgrass and Kentucky bluegrass. Thus golf courses infested with P. annua often require more water, fungicides and management (McCullough & Hart, 2009).
Chemical:\r\nHigh genetic variability in P. annua means that herbicides may be effective on some varieties, but other varieties are tolerant making complete control challenging. Rimsulfuron (TranXit GTA) may be effective at controlling infestations in Bermudagrass (Cynodon spp.) turf in the Southern United States. Bispyribac-sodium (Velocity) has had some success as a selective control of P. annua in bentgrass fairways (Christian, 2006). Ethofumesate (Nortron or Expo 500) can be used to kill annual bluegrass in ryegrass turf. Pendimethalin (Stomp) can be fairly safely applied over most turf to kill annual bluegrass as it germinates. A growth regulator called paclobutrazol is now being marketed in Australia to help with management of annual bluegrass in turf. In gardens, paths and waste areas annual bluegrass is susceptible to most herbicides. Selective grass herbicides such as fluazifop (Fusilade) can give very poor control of this particular grass; haloxyfop (Gallant) is the best to use (Massey University, 2008). \r\n\r\n\r\n
Physical: Manual removal by hand pulling or hoeing can be effective in early spring, but is very labour intensive and only feasible when infestations are small (GOERP, 2009).\r\n
Biological control: The bacteria Xanthomonas campestris pv. poae and Pseudomonas putida have had some successes in managing annual bluegrass infestations. A negative relationship between annual bluegrass and the amount of arbuscular mycorrhizal fungi in soil has been reported, although the opposite trend has been reported for another weed species Agrostis stolonifera (Gange et al., 1999).\r\n
Cultural: Good cultural practices tend to be the best way of dealing with annual bluegrass on turfs. Techniques to relieve soil compaction and aerate the soil will help desirable species compete well with annual bluegrass. Summer irrigation may assist annual bluegrass. Excess phosphate should be avoided. Dense swards of the desired turf species will stop new seedlings establishing, especially in autumn when germination of new annual bluegrass seedlings will be greatest (Massey University, 2008).