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

esults of grazing trails reported by Grech (2005a) at Greenvale, Victoria, showed that cattle reduced the amount of panicle seed
produced in comparison to ungrazed paddocks by 95%, and in comparison to sheep grazed paddocks by 77%, when stocking at a
normal rate for the district, at 12 Dry Sheep Equivalent ha -1 . Both sheep and cattle continued to gain weight over the spring.
Strategic grazing can be combined with spray-topping and/or wiping before flowering. Grazing management is predicated on
acceptance of N. neesiana as an ineradicable pasture component and making best use of the feed it offers. In pasture situations it
is a weed one can ‘learn to love’ (Storrie 2006).
Shade
Establishment of Pinus radiata to shade out N. neesiana is being investigated by Hawkes Bay Regional Council in New Zealand
(Slay 2002a). Five years after plantation establishment, N. neesiana was “weaker, rotting and forming a dense thatch” (Slay
2002a p. 33).
Quarantine and restriction of dispersal
Bourdôt (1988) recommended a range of measures to restrict seed dispersal: restricting livestock access to seeding plants,
appropriate mangement for contaminated stock, not harvesting fodder from infested land, cleaning of contaminated vehicles,
machinery and clothing, and eradication from flood-prone land. Additionally Liebert (1996) mentioned the use of only weed-free
fodder and seed, and not moving contaminated soil. These measures can be implemented by strategically timed slashing and
mowing, restricted grazing (including droving of livestock along infested roadsides), fodder harvesting (Liebert 1996, Frederick
2002), and vehicle movement, signage to alert people to N. neesiana presence, particularly on roadsides (Liebert 1996, Frederick
2002), machinery hygiene programs (Frederick 2002, Moerkerk 2006a), State-wide quarantine (DPIW 2007) and other measures.
The presence of stem cleistogenes requires that fodder harvested from infested swards at any time should not be fed out in
uninfested areas.
To minimise seed movement on livestock the Tasmanian Department of Primary Industries and Water has prescribed measures
in Regulations under the Weed Management Act 1999. The length of hairs on the coat is not to exceed 25 mm, seeds are not to be
adhering to the animal, a permit for importation is required and the animals must be imported to an approved facility or
slaughterhouse. Suggested actions include liaison with suppliers and confinement of the animals in holding pens until they have
been thoroughly inspected and have completed “bowel evacuation” (DPIW 2007 p. 3). Similar hygiene activities are
recommended for clothing, machinery, soil and other materials. Persons wishing to dispose of contaminated materials must
contact a government officer who shall determine whether removal to a quarantine place or destruction in situ is most
appropriate (DPIW 2007).
Integrated management in native vegetation
Spot spraying with glyphosate is the usual management method in natural or semi-natural areas (e.g. at Organ Pipes National
Park, McDougall and Morgan 2005). Repeated herbicide treatments are commonly required to kill mature plants (Muyt 2001)
and several cycles of treatment and monitoring are required for long-term control (Liebert 1996, Frederick 2002). Liebert (1996)
considered the residual activity of flupropanate made it unsuitable for use in native vegetation. Bedggood and Moerkerk (2002)
noted that investigations were underway in the ACT to determine spraying times when the native plants were dormant and thus
less likely to be impacted. However native C 3 grasses probably generally have similar growth periods to N. neesiana, so the
scope for such temporal selectivity appears very limited. Victorian experience is that native species are always damaged
(Bedggood and Moerkerk 2002, citing C. Hocking).
Liebert (1996) suggested that burning before November could help to kill seeds and promote germination of cleistogenes, which
could be sprayed with glyphosate the following autumn.
Lunt and Morgan (2000) recommended maintenance of dense swards of the dominant grass as the most efficient means of
limiting the establishment and density of N.neesiana in T. triandra grasslands, and re-establishment of dense T. triandra after
herbicidal control of N. neesiana. They reported slower and comparatively little invasion where T. triandra cover exceeded 50%,
and in one invaded grassland, proximity to large infestations did not appear to be a significant factor in determining the presence
of the weed in particular quadrats (Lunt and Morgan 2000). Oversowing of T. triandra does not appear to reduce the soil seed
bank of N. neesiana, possibly because the growing periods of the two species has little overlap, however Austrostipa or
Austrodanthonia spp. may be more suitable (Beames et al. 2005). Direct drilling of T. triandra seed after spraying has been
found to provide effective control (Liebert 1996 citing Craig Bray).
Current best practice management in invaded Themeda-dominated grasslands has been detailed by Beames et al. (2005) and
Hocking (2005b) and involves finely targetted biannual or more frequent glyphosate spraying before flowering, followed by
establishment of T. triandra. Fire can be integrated into these programs both to improve germination of native and N. neesiana
seeds and open up the landscape, and the broadcasting of native seeds is recomended. A brief case study of such an approach
was provided by Snell et al. (2007).
Muyt (2005) recommended selective mowing with catcher mowers at the edges of dense stands, but the scale and irregular
distribution of patches in most infestations make this approach impractibable.
In uninvaded grasslands, best practice management is focused on minimisation of major disturbance, and the maintenance of
existing native grass sward density and cover. Many herbicides used to control Nassella spp. have severe impacts on native
vegetation and can result in major weed invasion similar to those which occur after ploughing (Hocking 1998). As noted in more
detail above, when the dominant native grass dies or is killed by disturbance, the N and P held in the plant is released into the
soil, creating a nutrient flush which enables successful establishment of Nassella spp. (Henderson and Hocking 1997, Wijesuriya
and Hocking 1997, Hocking 1998).
A range of techniques have been developed for re-establishment of native grasses and replacement of N. neesiana in native
grasslands (McDougall 1989, Stafford 1991, Hocking 2005b) and have been recommended for use for paticular areas (e.g. Muyt
2005). However the development of effective techniques requires much improved understanding of the underlying ecological
processes (Hocking and Mason 2001).
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