Economic impact of paraquat in Australia

Paraquat herbicides have played an important role in crop protection in Australia for many years. There are no effective alternative herbicides to paraquat with its unique properties and mode of action. It is a vital part of weed control in many crops, both in its own right and in fighting resistance to glyphosate. This article summarises the findings of a recent report, explaining how paraquat benefits Australian farming and the country’s whole economy.

Role of paraquat

Paraquat is a non-selective


A chemical product used for eliminating all types of weeds (annual and perennial grasses and broadleaved weeds).

Authoritative On-line References and Resources An invaluable source of contemporary information about herbicides and weeds from Iowa State University.
herbicide controlling a very broad spectrum of weeds before sowing annual crops and in orchards, vineyards and other perennial crops.
Paraquat has properties that give many benefits as a herbicide. These include very fast action and rainfastness. The report1 indicated that in Australia several other benefits were regarded by farmers and other stakeholders as being especially valuable:
  • Paraquat is bound extremely tightly immediately on contact with soil clay particles and with organic matter. This means that paraquat can be sprayed right up to base of woody plants and that the bark of orchard trees and grapevines provides effective protection. Deactivation on soil contact means that paraquat does not leach


    The natural process by which water soluble substances are carried downward through the soil into groundwater.
    . It can be used safely in sugarcane plantations near the Great Barrier Reef, for example.
  • Paraquat is used to fight weed resistance to the critically important herbicide glyphosate. The rise of glyphosate resistant weed


    The inherited ability of a plant/weed to survive a dose of a herbicide normally lethal to that species.

    Authoritative On-line References and Resources The International Survey of Herbicide Resistant Weeds monitors the evolution of resistant species and assesses their impact. All confirmed instances of new cases are listed.
    species in Australia is summarised in Table 1. Paraquat has a different mode of action to glyphosate and is used very effectively in the ‘double-knock’ technique.
  • Paraquat has many other uses including ‘spray-topping’ to improve the quality of pastures.
Table 1. Glyphosate resistant weeds in Australia and dates of first confirmations of resistant populations.
Species New South Wales Queensland South Australia Victoria Western Australia
Lolium rigidum (Rigid ryegrass)  1997 X 1999 1996 2003
Echinochloa colona (Jungle rice)  2007 2009 X X 2010
Urochloa panicoides (Liverseed grass) 2008 X X X X
Chloris truncata (Windmill grass)  2010 X X X X
Conyza bonariensis (Hairy fleabane) 2010 2011 2011 X X
Bromus diandrus (Ripgut brome) X X 2011 X X
Sonchus oleraceus (Annual sowthistle) 2014 X X X X

Estimating value

Three approaches were used to estimate the value of paraquat to the Australian economy over 10 years. One method was to simply take the total amount Australian farmers spend on paraquat herbicides and add the cost of application. This assumes that the cost is at least recouped by farmers in the extra value of their crops or they would not buy it at that price. This would be expected to be the smallest estimate of value, because, in fact, benefits worth considerably more than the cost would be expected in order to make the purchase worthwhile. The second method was based on the conclusion from a study by CropLife America that, as a whole, herbicides account for 25% of the total value of crop production, ie without herbicides competition from weeds would reduce yields by 25%. Accounting for actual use of paraquat as a proportion of all herbicides used in the relevant crops gives an estimate of the value of paraquat in terms of crop output. The third method recognised paraquat’s role in the context of other weed control methods, in particular, in mitigating the proliferation of glyphosate resistant weeds. Without paraquat, glyphosate resistant weeds would become a much more serious problem, which would have a considerably greater impact on crop yields in reality. Figure 1: Estimates of the value of paraquat to the Australian economy over 10 yearsThe estimated values of the use of paraquat in Australian agriculture over a 10 year period calculated by these methods range from $AUS 570 million - $AUS 1800 million and are illustrated in Fig. 1. In addition, the use of paraquat brings benefits to employment and foreign trade. You can read more about the benefits of paraquat here.

Other articles on the benefits of paraquat to Australian agriculture

Several articles in The Paraquat Information Center attest to the benefits of using paraquat in Australian agriculture. These include:

Spray-topping with paraquat improves cereal-grass rotations

Paraquat can be used to improve the species composition of pastures for livestock grazing and reduce the carryover of grass weed


The leaves are "narrow" as opposed to the "broad" leaves of broadleaved weeds. Also called 'monocots' having one seed leaf opposed to 'dicots' having two seed leaves.

Authoritative On-line References and Resources

The International Weed Science Society represents individual associations around the world. 
seeds into following cereal crops. The technique used is known as spray-topping.
Read more

Paraquat protects glyphosate in Aussie double-knock

Australian researchers have found that spraying paraquat in a ‘Double Knock’ system is a very effective way to restrict the evolution of glyphosate resistant weeds. Survivors of glyphosate burndown are sprayed with paraquat up to two weeks later. The Double Knock ensures that weeds are hit with two different modes of action. Read more

Four more weeds develop resistance in Australia

Resistance to glyphosate was suspected in four new weed species in 2007. Three of these were subsequently confirmed. Read more

Barnyardgrass develops herbicide resistance

In 2007, Echinochloa colona (barnyard grass, jungle rice) was confirmed as having developed resistance to glyphosate. Previously, only resistant populations of Lolium rigidum (rigid ryegrass) had been observed. Read more


Deloitte Access Economics (2013). The economic impact of paraquat.


The brand name of the leading paraquat product in Australia and in around 90 other countries is Gramoxone. Another popular product in Australia is a mixture of paraquat and diquat sold as Spray.Seed.