Herbicide resistance in wild radish, brome and barley grass populations randomly collected in Australian surveys

Abstract

The GRDC-funded random surveys conducted in Australia at harvest in 2020 reveal that herbicide resistant weed populations are common. However, the incidence of resistance varies significantly for weed species both within cropping regions and across Australia. Nationally, 130 wild radish, 382 brome grass and 251 barley grass populations were collected from cropping fields in WA, SA, Vic, Tas, NSW and QLD at harvest and were treated with a range of herbicides.
In wild radish, high levels of resistance to chlorsulfuron, imazamox+imazapyr (Intervix) and 2,4-D were detected. For the ALS-inhibiting herbicide chlorsulfuron, 71% of populations were resistant, with 47% of populations having cross resistance to the ALS herbicide mixture Intervix. Resistance to the synthetic auxin 2,4-D was observed in 37% of populations. Resistance to other herbicides was low, 15% of populations were resistant to diflufenican, only 3% of populations (all from WA) were resistant to atrazine, while developing resistance to pyrasulfotole+bromoxynil was observed and no resistance to glyphosate was detected. Herbicide resistant wild radish populations were more common in WA than in the other states.
Brome grass and barley grass were screened to quizalofop, clethodim, Intervix, sulfosulfuron and glyphosate. For brome grass, 29% of populations were classed as resistant to sulfosulfuron and a further 10% classed as developing resistance. Sulfosulfuron resistance was found in all states, although resistance to the other herbicides was low and varied between states. For barley grass (screened with paraquat in addition to the herbicides listed above), resistance was generally low for all herbicides across all states, although no resistance to glyphosate was detected. Continual monitoring of the distribution, incidence and frequency of herbicide resistance, and analysis of changes over time, will aid management decisions of farmers and agronomists.