Page 1 Page 2 Page 3 Page 4 Page 5 Page 6 Page 7 Page 8 Page 9 Page 10 Page 11 Page 12 Page 13 Page 14 Page 15 Page 16 Page 17 Page 18 Page 19 Page 20 Page 21 Page 22 Page 23 Page 24 Page 25 Page 26 Page 27 Page 28 Page 29 Page 30 Page 31 Page 32 Page 33 Page 34 Page 35 Page 36 Page 37 Page 38 Page 39 Page 40 Page 41 Page 42 Page 43 Page 4429 IREC Farmers' Newsletter No. 197 — Autumn 2017 The recent discovery of flaxleaf fleabane resistance to paraquat is a clear warning to crop producers that there is no room for complacency with double knock operations. grain producers that there is no room for complacency following a double knock operation. In addition to this recent discovery, an annual ryegrass population from a Western Australian vineyard was confirmed in 2013 to have resistance to both glyphosate and paraquat. This shows that a single plant can develop resistance to both of the main non- selective knockdown herbicides used in Australian grain production.” Paraquat is a widely-used herbicide, being an active ingredient in over 100 herbicide products registered for use in broadacre cropping. It is a group L herbicide and as such is considered a ‘moderate risk’ for herbicide resistance. Having a moderate risk rating means that resistance generally takes longer to occur, not that it won’t occur. “Paraquat resistance typically takes over 15 years of consistent use before resistant weeds are noticeable in the field,” said Mark. “This critical period has now elapsed on many farms where paraquat is used in cereals and broadleaf crops, and for general weed control around the farm.” Paraquat resistance has been present and widespread in barley grass in lucerne production systems for many years in southern NSW and Victoria (Table 1). While paraquat resistance is still relatively rare in other systems, very high level resistance was confirmed in three weed species (crowsfoot grass, blackberry nightshade and cudweed) taken from sugarcane and tomato blocks around Bundaberg in 2015 (Table 1). In the event of widespread resistance to paraquat, Mark is concerned that there are no new herbicide modes of action likely to be commercialised within the next 10 years or more, so we need to protect what we have. Species Common name Year State Crop Hordeum glaucum Northern barley grass 1983 Victoria lucerne Arctotheca calendula Capeweed 1984 Victoria lucerne Hordeum leporinum Barley grass 1988 Victoria lucerne Vulpia bromoides Silver grass 1990 Victoria lucerne Mitracarpus hirtus Small square weed 2007 Queensland mangoes Lolium rigidum Annual ryegrass 2010 South Australia pasture seed Gamochaeta pensylvanica Cudweed 2015 Queensland tomatoes sugar cane Solanum nigrum Blackberry nightshade 2015 Queensland tomatoes sugar cane Eleusine indica Crowsfoot grass 2015 Queensland tomatoes sugar cane Conyza bonariensis Flaxleaf fleabane 2016 NSW grape vines Table 1. Weeds with confirmed resistance to paraquat in Australia. Source: