herbicide. Although twice as expensive as using a single glyphosate spray, the "Double Knock" system is widely relied upon by farmers as a resistance management strategy. Nevertheless, herbicide resistance has been seen for both herbicides in Western Australia. A computer simulation showed that with alternating annual use between glyphosate and paraquat, only one field in five would be expected to have glyphosate-resistant annual ryegrass (Lolium rigidum) after 30 years, compared to nearly 90% of fields sprayed only with glyphosate. A "Double Knock" regime with paraquat cleaning-up after glyphosate was predicted to keep all fields free of glyphosate resistant ryegrass for at least 30 years. Toxicity Paraquat is toxic to humans (Category II) by the oral route and moderately toxic (Category III) through the skin. Pure paraquat, when ingested, is highly toxic to mammals, including humans, causing severe inflammation and potentially leading to severe lung damage, acute respiratory distress syndrome (ARDS), and death. The mortality rate is estimated between 60-90%. Paraquat is also toxic when inhaled and is in the Toxicity Category I (the highest of four levels) for acute inhalation effects. For agricultural uses, the EPA determined that particles used in agricultural practices (400–800 μm) are not in the respirable range. Paraquat also causes moderate to severe irritation of the eye and skin. Diluted paraquat used for spraying is less toxic; thus, the greatest risk of accidental poisoning is during mixing and loading paraquat for use. The standard treatment for paraquat poisoning is first to remove as much as possible by pumping the stomach. Fuller's earth or activated charcoal may also improve outcomes depending on the timing. Haemodialysis, haemofiltration, haemoperfusion, or antioxidant therapy may also be suggested. Immunosuppressive therapy to reduce the inflammation is an approach suggested by some, however only low certainty evidence supports using medications such as glucocorticoids with cyclophosphamide in addition to the standard care to reduce mortality. It is also unknown if adding glucocorticoid with cyclophosphamide to the standard care has unwanted side effects such as increasing the risk of infection. Oxygen should not be administered unless SpO2 levels are below 92%, as high concentrations of oxygen intensify the toxic effects. Death may occur up to 30 days after ingestion. Lung injury is a main feature of poisoning. Liver, heart, lung, and kidney failure can occur within several days to weeks that can lead to death up to 30 days after ingestion. Those who suffer large