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Poa Seed

Poa Seed

Poa Seed

Poa annua can have either a tufted, slightly creeping or creeping (prostrate) growth habit depending on the genotype due to the extremely diverse grass species. There are commonly two forms of Poa annua which include an annual genotype, which is commonly tufted and a perennial genotype, which is (semi-)prostrate. Huff (2002) goes even further and breaks down the perennial genotype into two further categories, (i) a short lived, perennial type adapted to various turf (lawns, fairways, tees etc.) referred to as a “turf-type”, and (ii) a long-lived, perennial type that thrives under the extremely close mowing heights of golf greens, referred to as “greens-type”. The variation present within the species allows herbicide resistance and a high degree of regenerative potential.

Poa

Culms (stems) of the Poa annua plant can be up to 30 cm if left unmown. The soft, narrowly linear, flat, smooth leaves are up to 3.5 mm wide. Foliage is often lime green in colour for the annual genotypes and darker green in colour for the perennial genotypes. In rare instances a Poa plant can have no inflorescence or more commonly they can produce multiple to several inflorescence (panicles) which can grow up to 7 cm if left unmown. Perennial genotypes often produce fewer inflorescences and form patches from short stolons (McCarty et al., 2008). Spikelets of the inflorescence are up to 5.5 mm are closely spaced with 3-7 flowers (Darke et al., 1994). Poa has a shallow fibrous root system that can establish well, particularly if the Poa annua plant or plants are within a routinely mown, well maintained sward.Annual and perennial biotypes exist. Both forms produce by seed plus short stolons for the perennial biotypes. The annual genotype can complete its lifecycle in approximately 2 months. However, during this short period, substantial damage can take place if seed is able to germinate freely. It has been estimated that annual Poa seed densities are commonly 200,000 per square metre in infested lawns, which is equivalent to 20 seeds in every square centimeter (Massey University, 2013). Poa annua can flower and establish at any time of the year, although this is less likely under dry conditions. Inflorescence emerge after a growing point changes from the vegetative to the reproductive state. Subsequent elongation of the stem (now called a flowering culm) elevated the inflorescence so that developing seed can disperse and provide new plants when conditions for germination and seedling growth are favorable (Turgeon, 2003).

Annual Poa annua predominantly dominates turf that is weakened by wear, deficient in nutrients, excessively wet and grows in compacted soil. Perennial Poa is usually found within closely mown golf courses, within tees to greens under routine high maintenance, Both biotypes are seen in major sports stadia across Australia that either has a standalone ryegrass (Lolium spp.) or combination of green couch (Cynodon spp.) and ryegrass playing surface. It is likely that Poa seed has been brought in by various means (wind, footwear, unclean machinery, contamination etc.). Poa annua prefers a pH of 6 to 7 and flowers prolifically at very low cutting heights which also disrupts the quality and appearance of the turf surface.“In the USA approximately 80% of Poa annua germination occurs in the autumn in a 60 day window; studies here in Australia indicate that the main flush of germination also occurs in the autumn with some germination occurring in the spring. However, the more perennial types can flower all year round with a major pulse in the late winter and spring (Neylan and Peart, 2009).” The potential for an explosive weed population is possible given there is often a very large seed bank. Seedbank persistence can be 4-6 years (WAH, 2013). Favorable environmental triggers include: (Source: turffinder.com)

 

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