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

Storrie and Lowien 2003). However under Victorian legislation governing pesticide use these permits did not legalise use: offlabel
use, with certain provisions, not being illegal.
Label registration for all Nassella species was finally achieved for a flupropanate product in 2004 (McLaren et al. 2005). Label
recommendations were for application to actively growing plants, by boom or spot spraying, once per year, in urban open space,
woodlands, roadsides, nature reserves and pastures. Other products with on-label uses soon followed. As of October 2007 the
only other herbicide with specific label recommendatons for N. neesiana was glyphosate, registered only for spot spraying,
although a number of minor use permits were in operation (Snell et al. 2007).
Glyphosate
Glyphosate prevents synthesis of essential aromatic amino acids. It is probably the world’s most widely used herbicide. It is a
non-selective, systemic, water soluble herbicide, absorbed by foliage, rapidly translocated throughout the plant and non-residual,
being inactivated on contact with soil (Tom.lin 1997). It has relatively rapid activity, kills all plants, and creates bare ground, so
when there is a soil seed bank of N. neesiana the plant quickly re-establishes (Liebert 1996). Pritchard (2002) found it gave
excellent initial control, preventing seed formation when applied at the boot stage, but that 10 months after application many
tussocks showed new growth.
Off-target damage from glyphosate can be high, but depends on the selectivity of the application method. There is no
withholding period for livestock grazing or other agricultural activity although stock grazing should not be undertaken for 7 days
after application (Snell et al. 2007)..
Flupropanate
Flupropanate (flupropanate-sodium, formerly called tetrapion) is an halogenated (fluorine) alkanoic acid which functions as an
inhibitor of fat sysnthesis. It is a water soluble, systemic herbicide with low contact activity, taken up mainly by roots, and used
only for control of perennial and annual grasses in pastures and uncultivated areas (Tomlin 1997). It is moderately selective and
slow acting, with soil residual effects that kill emerging seedlings (Parsons and Cuthbertson 1992, McLaren et al. 2005).
Recommended rates for control of mature N. neesiana are 1.5-3 L ha -1 (Grech et al. 2009a). Effects on target plants may be
noticeable after 3-5 months but it may take upt to 12 months for plants to die (Snell et al. 2007). Pritchard (2002) found only
slight foliage death 15 weeks after treatment but recorded 92-95% kill of tussocks after 45 weeks. The residual effects are
increased at higher application rates and their duration is dependent on rainfall, which leaches the herbicide from the soil
(Michelmore 2003). Fluporanate activity and behaviour is dependent on soil type – higher rates are used on fertile basalt soils
and in higher rainfall areas, lower rates on infertile soils derived from sedimentary and granitic rocks and in lower rainfall areas
(Snell et al. 2007). Flupropanate provides some selectivity: Austrodanthonia, Austrostipa spp. and Microlaena are killed,
especially at higher applications rates, while T. triandra, Bothriochloa macra and Poa labillardieri Steud. are generally tolerant
at label rates. Phalaris aquatica L., Dactylis glomerata L. and Festuca arundinacea are affected but recover, while young
Trifolium subterraneum L. are severely affected (Michelmore 2003). In Australia, a withholding period for grazing stock or
cutting for stock food of 4 months minimum after blanket application is mandatory, and 14 days for spot application, along with
some other restrictive provisions for production agriculture (McLaren et al. 2005).
Flupropanate has been the preferred herbicide for spot spraying in agricultural areas and on land lacking significant native cover
(Liebert 1996). An infestation in Geelong, originally with 80% cover, was reduced to 10% cover after spraying in 3 consecutive
years and the broadleaf weeds that initially colonised were short-lived and some native grasses began to establish (Liebert 1996).
Grech (2007a) found that set-stocking combined with flupropanate spraying resulted in more bare ground and an increase in
infestations. Of the range of herbicide and stocking options examined, flupropanate combined with strategic grazing and pasture
rehabilitation provided the best control. Grech et al. (2009b) found that low rate treatments with flupropanate (0.25 and 0.75 L
Ha -1 ) we ineffective in controlling N. neesiana seedlings. Grech et al. (2009a) found that flupropanate at 2 L Ha -1 effectively
controlled N. trichotoma in pot trials, but not N. neesiana, and that a range of native and exotic grasses was unaffected apart
from a transient decline in growth.
A major disadvantage of flupropanate is the creation of bare ground that persists for long periods (Snell et al. 2007). These areas
may be prone to subsequent reinvasion.
2,2-DPA
2,2-DPA is an halogenated alkanoic acid which acts by precipitation of protein (Tomlin 1997). It is a systemic herbicide
absorbed by leaves and roots, used mostly for control of annual and perennial grasses (Tomlin 1997). It is selective for some
grasses at low rates, and at high rates provides non-selective control of monocots (Parsons and Cuthbertson 1992). It is generally
considered to be less effective and useful than the two most favoured herbicides, and does considerably more damage to nontarget
species than flupropanate (Michelmore 2003). Pritchard (2002) found it quickly killed foliage, but 45 weeks after
application had only reduced the number of tussocks by 40%. Hartley (1994) found that 2,2-DPA reduced seed production by
90-99%, but detected resistance to 2,2-DPA in New Zealand after 2 years of annual or biannual application.
Hexazinone
Hexazinone is an inhibitor of photosynthesis and is a non-selective contact herbicide, absorbed by leaves and roots (Tomlin
1997), mainly the latter (Parsons and Cuthbertson 1992). It has a long residual life in soil (Parsons and Cuthbertson 1992) and
maintains bare ground for long periods, and is available commonly in granular preparations.
Triazines
Atrazine is a triazine chemical which acts by inhibiting photosynthesis. It is a water soluble, selective systemic herbicide,
absorbed mainly through the roots but also through foliage, mainly used to control broadleaf weeds and annual grasses (Tomlin
1997). It is relatively rapid acting and has pronounced residual effects for 6 months or more after application (Parsons and
Cuthbertson 1992). Simazine is another triazine compound that acts by inhibiting photosynthesis. It is mainly root-absorbed and
provides selective pre-emergence control of grasses and broad-leaved weeds, with long residual control at high application rates
(Parsons and Cuthbertson 1992). Pritchard (2002) found that both atrazine and simazine application at the boot stage resulted in
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