Literature review: Impact of Chilean needle grass ... - Weeds Australia

8.4 and 9.3 respectively (Slay 2001, Slay 2002a). The minimum maintenance level of crude protein for livestock is 7% (Slay
2001). Gardener et al. (1999 p. 10) compared N. neesiana productivity and feed analysis with Festuca arundinacea, and Grech
(2007a) compared it with Dactylis glomerata.
Flowering and fruiting
According to Barkworth and Torres (2001 p. 462) and Barkworth (2006) Australian populations “do not appear to set seed in the
exposed inflorescences”. These erroneous statements are possibly based on a few herbarium specimens collected during drought
conditions.
Plants in their first year of growth do not flower (Sethu Ramasamy pers. comm. 13 June 2007). Benson and McDougall (2005)
provided the primary juvenile periods of many other grasses but failed to provide one for N. neesiana. No definitive published
information appears to be available on the juvenile period.
The factors that trigger a shift from vegetative to reproductive growth, are partially known. Low winter temperatures are
necessary for vernalization (Gardener et al. 1996b). (See Sinclair 2002 for the variety of factors involved in floral inducation in
grasses). Rainfall appears to play a role. In southern Victoria bolting generally commences in mid October (D. McLaren, 26
October 2006).
According to Gardener et al. (2003a) the main ‘flowering’ period is November to February in Australia and October to January
in South America (based on herbrium specimens) with some flowering as late as May. Near Guyra on the Northern Tablelands of
NSW ‘flowering’ commenced between early October and early November and finished between early March and late April
(1994 and 1995, Gardener et al. 2003a). Two separate flowering periods were observed near Guyra in 1995, but not in 1996 or
1997. However Gardener et al. (2003a, etc.) had a very broad, inaccurate definition of ‘flowering time’ covering the period from
the first emergence of the panicle from the leaf sheath to the time when the last mature seeds were dropped.
Burkart (1969) may be more accurate, giving the flowering period in Argentina as October and November. In south western
Europe, flowering occurs from May to July (Verloove 2005). Slay (2002c) is pehaps most specific, stating that anthesis
(flowering) occurs around mid-November in New Zealand, while Slay (2001) observed flowering over a period of approximately
17 days from mid to late November in an infestation at Waipawa, New Zealand. In Australia, according to Cook (1999), panicle
production occurs from late spring to early summer, sometimes with a secondary, much less prolific, flush in autumn. Snell et al.
(2007 p. 8) noted that there is “a second panicle seeding period during autumn” in northern NSW. Bedggood and Moerkerk
(2002) state that flowering occurs from early October through to March or April and that panicle seed are produced in autumn in
northern areas. In the ACT N. neesiana usually flowers from November to February (ACT Weeds Working Group 2002). In
South Australia flowering or fruiting inflorescences are present in November and December (Jessop et al. 2006). Flowering in
Victoria is mostly October to February (Walsh 1994) and in Australia generally from spring to early summer with occasional
plants to April (McLaren, Stajsic and Iaconis. 2004).
According to the ACT Weeds Working Group (2002) and Ens (2005 citing Ens 2002a) N. neesiana “ has the ability to flower all
year round” given favourable environmental conditions. Bedggood and Moerkerk (2002) recorded that it will flower in response
to summer rain. High density of tiller production (and thus seed production) appears to require consistent rainfall during the
reproductive period (Gardener et al. 2003a). Slay (2002c) noted that a second flush of panicles can be produced if the normal
late spring panicles are removed by mowing or grazing, and that isolated plants are more likely to have a secondary flowering
period than plants in dense populations.
The flowering periods recorded mostly appear to apply to large populations in broad areas. No information seems to be available
on site specific aspects of flowering, the proportion of the population that has a particular floral phenology, or the individual
variation of a single plant. There is no indication of the duration of flowering on a particular panicle or the sequence and timing
of individual flower opening and closing on a panicle. The time of day that the flowers open and their period of opening do not
appear to have been recorded. Information about the timing of fertilisation, the period of receptivity of the stigma, the period
between pollination and fertilisation and between fertilisation and embro development have rarely been determined for any
plants (de Tirquell 1986) and are unknown for N. neesiana.
The period from flowering to seed maturation is about 7 weeks (Liebert 1996). According to Slay (2002c), seed became viable
within 8 days of flowering, 76% of seed was still ‘soft’ after 14 days, with 60% viable after 22 days. In New Zealand most seed
reaches full maturity between late December and early January and is quickly shed, but seed produced on sub-panicles that
emerge from stem nodes matures later (Slay 2002c).
The seed is a velate caryopsis, i.e. the caryopsis falls free of other spikelet parts (Sendulsky et al. 1986). Panicle seed matures
and is shed from mid to late summer (Gaur et al. 2005), generally in mid December in southern Victoria (D. McLaren, 26
October 2006). Near Guyra on the Northern Tablelands of NSW most seeds matured between late December and mid-February
(1994 and 1995, Gardener et al. 2003a), and was generally shed in December-January (Gardener et al. 2003ba). Slay (2001)
noted that panicle seed at one site was almost all shed simultaneously in early January 2001. Most panicle seed has been shed by
late February in NSW (Duncan 1993) and this is the case in Victoria (Liebert 1996). Stem cleistogene seed from ensheathed
inflorescences matures later than panicle seed, in February (Slay 2002a). In the Melbourne region in 2006 under drought
conditions, most panicle seed was shed in November-December, largely in late November-early December (pers. obs.). Puhar
(1996) noted that seed began to drop at St Albans, Victoria, in early January 2006.
Slay (2002c) modified the Feekes Scale used to define the growth stages of cereals to classify the reproductive growth stages of
N. neesiana (Table 2).
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