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

Vertebrates
Many stipoid grasses are readily eaten by livestock, including N. neesiana. In the Great Basin region of the USA Stipa spp. sens.
lat. are considered “for the most part valuable forage plants” (Hitchcock and Chase 1971 p. 445). N. neesiana is readily eaten by
sheep, cattle and horses in Argentine pastures in winter and spring, but consumption is much reduced when the plant is flowering
and seeding, except under drought conditions or when stocking rates are high (Gardener et al. 1996b, Gardener 1998). It has
been rated as one of the most valuable winter pasture species in the pampas (Gardener et al. 1996b).
Grasses defend themselves against grazing mammals in a variety of ways, including adaptations of form, habit and phenology,
presence of indigestible structural compounds and presence of toxic chemicals. Very few grass species contain toxic secondary
metabolites that deter grazing and herbivory: less than 0.2% contain alkaloids, and the presence of noxious terpenoids and
cyanogenetic compounds is rare (Tscharntke and Greiler 1995, Witt and McConnachie 2004), although McDonald (1991)
claimed that defensive metabolites are common in cereal and other grasses. Records of toxic effects of stipoids on livestock are
scarce. According to Quattrocchi (2006 p. 1361) “Some” Nassella species “have caused poisoning to mammals”. Randall (2002)
stated that N. neesiana has been recorded as toxic, and the US Food and Drug Admimistration Poisonous Plants Database
(USFDA 2006) lists N. neesiana, citing Kellerman et al. (1988).
Probably most cases of toxicity attributed to grasses are the result of grass fungi. Possibly the best known example is ergot,
Claviceps purpurea, which infects cultivated Secale cereale L., other cereals, and other grasses, the toxic effects of which have
resulted in mass human poisonings (Gair et al. 1983, Wink and Van Wyk 2008). However none of the many Claviceps species
affect Stipeae (Wink and Van Wyk 2008). The Mexican and southwestern USA Achnatherum robustum (Vasey) Barkworth (=
Stipa vaseyi Scribn. = Stipa robusta (Vasey) Scribn.), known as Sleepy Grass, allegedly acts as a “narcotic”, especially on horses
(Hitchcock and Chase 1971) due to infection with endophytic Acremonium fungi. The active principles were identified by
Petroski et al. (1992), the dominant one, lysergic acid amide, likely being responsible for a reportedly extreme “sedative” effect
on animals. However lysergic acid and its derivatives are generally considered to be hallucingens, producing delerium but not
sedation (Wink and Van Wyk 2008). Achnatherum inebrians (Hance) Keng of China and Mongolia, known as Drunken Horse
Grass, probably affects animals by ergot alkaloids produced by the endophytic Neotyphodium gansuense Li and Nan
(Clavicipitaceae) (Moon et al. 2007). The ergot alkaloids consist of two main series, clavine alkaloids and the lysergic acid
amides (Wink and Van Wyk 2008). Such fungal endophytes occur widely in grasses (see section on “Other biotic relationships”
below) and produce a variety of poisonous secondary metabolites that effectively deter pathogen attack and grazing, and
sometimes poison mammals (Tscharntke and Greiler 1995, Jallow et al. 2008), and are thus generally considered to be
symbionts, rather than pathogens (Wink and Van Wyk 2008).
Grass poisoning can also be caused by organic acids, which irritate skin and mucous membranes (Wink and Van Wyk 2008).
Stipa capensis contains glycosides producing a strong acid that can harm cattle (Tsvelev 1984).
Specialist granivorous birds, of which the most important are finches, parrots and pigeons, probably commonly consume stipoid
seeds, however there appear to be few relevant records. Twigg et al. (2009) found from anyalysis of stomach contents that seeds
in the diets of Australian finches (two Emblema spp.) and Alcedinidae (three dove and pigeon spp.) were predominantly