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

neesiana seeds are similar to those of some of the more robust seeded Austrostipa spp. which McBarron (1976 p. 135)
considered to be “undoubtedly ... the major cause of seed troubles for livestock, especially sheep in New South Wales”. These
Austrostipa spp. are commonly cited as one of the main undesirable attributes of native pastures, requiring timely destocking to
avoid problems (Garden et al. 2000). Seeds of Austrostipa spp. penetrate the eyes, mouthparts (Whittet 1969), skin and flesh
(Mulham and Moore 1970) of sheep. “Wrinkled, long-woolled and young sheep are particularly susceptible ... the wrinkles and
long wool collecting more of the seed, and the softer skin of young sheep allowing easier and deeper penetration. Severe damage
to the eyes, jaws and feet can be caused by the seeds, which have also been known to penetrate the abdomen and internal organs
... in extreme cases blindness, lameness, fever and death can result” (Mulham and Moore 1970 p. 105). Austrostipa and Aristida
spp. are the most common contributors to ‘vegetable fault’ (plant contamination) of wool in Australia (Grice 1993).
N. neesiana seeds are an irritant of skin (Wells et al. 1986) and “readily bore into the skins of animals, causing painful wounds”
(Hayward and Druce 1919). Irritation of livestock by attached seeds causes discomfort and loss of condition (Wheeler et al.
1990). Lambs appear to be particularly susceptible to eye injury (Bourdôt and Ryde 1986).. Infestation of livestock with seeds
may be exacerbated by rain, as happens with Austrostipa (McBarron 1976). The hides of cattle are too thick for the seed to
penetrate (Gardener et al. 1996b) but cattle may suffer injuries to the mouth and intestinal tract. The seeds “cause discomfort”
for dogs and humans (Liebert 1996), and can injure pet animals (Snell et al. 2007) and could be expected to cause a range of
serious medical problems based on their similarity to other stipoid seeds (see McBarron 1976). Awned seeds in general can
readily penetrate the soft tissue of the buccal and gastrointestinal tracts, producing inflammation, abcesseses and tooth and gum
disease (McBarron 1976). They may pass through the skin into muscle and can occasionally penetrate internal organs,
potentially causing fatal injuries (McBarron 1976). However penetration of skin, carcases and eyes by N. neesiana seeds is rare
on the northern tablelands of NSW (Cook 1999).
The seeds are a contaminant of wool (Hayward and Druce 1919, Wells et al. 1986, Auckland Regional Council 2002). The halflife
of seeds in the coats of sheep exposed to seeding plants for 17 days and then removed from exposure was measured at 7.5
days, with nearly half the seed remaining embedded after 100 days and only very slow subsequent seed loss (Gardener et al.
2003a). Upon removal of exposure, half the seeds on sheep had the callus embedded in the skin, but this reduced to 5% after 35
days, and few seed penetrated through the skin into flesh (Gardener et al. 2003a). The seeds damage pelts, and reduce the quality
of carcases and hides (Bourdôt and Ryde 1986, Bourdôt and Hurrell 1992, Slay 2002, Auckland Regional Council 2002).
In the context of livestock grazing N. neesiana is a ‘conflict of interest’ species (Grice 2004b) because it is a valuable fodder for
much of the year (Gardener 1998, Grech et al. 2004, Grech 2007a). Although it has harsh, often hairy leaves and tall course
culms (Connor et al. 1993), it is considered to produce moderate quality, palatable forage during winter and early spring (Slay
2002c) and to be of “modest” grazing value (Connor et al. 1993). In Argentina “it produces fairly good fodder” (Hayward and
Druce 1919 p. 228) and is considered one of the most important winter grazing species, valued because of its perenniality,
persistence, long life and good quality feed with relatively high crude protein levels in the young foliage (Gardener 1996,
Gardener et al. 1999). Its undesirability as a pasture species results not only from the problems caused by the seeds but from the
rapid reduction in foliage that accompanies the production of large numbers of unpalatable flowering stems in late spring and
summer, which results in a large seasonal reduction in carrying capacity at a critical time of year. Livestock avoid the plant in its
reproductive phase, so it gradually displaces more valuable pasture grasses (McWhirter et al. 2006). Its feed value (crude protein
and digestibility) is less than that of deliberately grown pasture grasses at the same stage of growth (Gardener et al. 1996b,
Gardener 1998, Cook 1999). It generally has a lower feed value than the widely cultivated, moderate feed value Dactylis
glomerata and is less reponsive to applications of N fertiliser (Grech et al. 2004, Gaur et al. 2005). But it responds well to
clipping (as a simulation of grazing), the regrowth sward after clipping having significantly higher crude protein, metabolisable
energy and digestible dry matter contents than growth in unclipped swards (Grech et al. 2004). Fertilisation and clipping can be
used to improve its usefulness as fodder (Grech et al. 2004) but grazing can promote its dominance when pasturage consists of
more palatable species (Liebert 1996, Gardener 1998).
N. neesiana is undesirable also because it can contaminate other agricultural produce, including hay (Frederick 2002).
Increased fire risk has rarely been seen as a problem. Bartley et al. (1990) argued that “the greater height and density” of N.
neesiana swards at Laverton North Grassland Reserve presented “a much greater fire hazard than native grasses”. According to
Liebert (1996 p. 9): “Regional fire authorities recognise the fire risk ... and consequently slash swards from November to
December”. However, comparative biomass production and breakdown assessments appear to be lacking and there appears to
have been no proper evaluation of fire risk, which should involve comparisons with alternative vegetation states.
All plants deplete soil moisture and the amounts of water used at particular times may have implications for co-occuring species
or have a wider ecological impact. Slay (2001) observed that soil moisture in early January under a dense ungrazed sward was
20.8%, while where the sward had been sprayed with glyphosate at flowering time it was 26.6% due to reduced transpiration and
the reduction of evaporation due to dead thatch. Infestations in T. triandra grasslands presumably deplete soil moisture in spring
and early summer, at the same time as the inter-tussock species are growing and before the main growing period of T. triandra.
The overall effect could be a premature drying-out of the grassland landscape.
Like other weeds N. neesiana can have beneficial impacts, although apart from its fodder value, these have hardly ever been
recorded in its invasive range. Slay (2002a) noted that well stablished populations can provide erosion control on steep land.
Control and management
N. neesiana is difficult to control and according to Gardener and Sindel (1998 p. 78) there is “overwhelming evidence” that it is
“almost impossible to eradicate” because of the difficulty of killing mature plants, the size and longevity of the soil seed bank
and the production of basal cleistogenes. Gardener et al. (1996a p. 243) considered there then existed “no widely successful
management techniques which result in the eradication or long term reduction”, while Gardener et al. (2003a p. 613) judged that
“chemical and mechanical control have had little success to date, at best temporarily slowing its spread”. Slay (2002c p. 24)
considered that the “overall tenacity” of Chilean needle grass made it “an extremely stubborn weed to manage and control”. He
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