Field survey of flupropanate-resistant Nassella trichotoma in Victoria

A population of Nassella trichotoma (serrated tussock) in Victoria was confirmed as resistant to flupropanate (sodium 2,2,3,3-tetrafluoropropionate) at a property north-west of Melbourne in 2002. To determine the spread of flupropanate resistance, 87 N. trichotoma plants were collected randomly from paddocks and on roadsides within 5 km of the resistant plants in 2003. A pot-dose method of resistance assessment identified plants resistant to flupropanate up to 3.5 km from the site where resistant plants were initially identified. Seeds from these plants showed 0.100% resistance, with sensitive plants often having a low (.5%) level of resistant seed. These results suggest movement of flupropanate resistance through seeds or pollen and show that its spread had occurred within one year of detection. This research emphasises the importance of integrated weed management and the need to rotate herbicide groups to avoid the ris