New light on wild radish evolution

Key points

  • Wild radish is one of the top-five weed challenges for Western Australian growers
  • WA wild radish populations have become 30 per cent more resistant to Group B herbicides in the past seven years.

New AHRI research shows that wild radish can adjust its flowering time in response to control techniques 

New research in Western Australia shows wild radish (Raphanus raphanistrum) is genetically capable of adapting to changing farming systems by modifying its flowering time to ensure survival.

This widespread, highly competitive and prolific weed is becoming harder to control, especially in the northern wheatbelt.

Past surveys by the Australian Herbicide Resistance Initiative (AHRI) have shown an increasing trend in wild radish populations with resistance to Group B herbicides across the WA wheatbelt – from 54 per cent in 2003 to 84 per cent in 2010.

In that period, there was a spike in wild radish resistance to 2,4-dichlorophenoxyacetic acid (2,4-D) from 60 per cent to 76 per cent and resistance to multiple herbicide chemistries was found.

AHRI is repeating its wild radish resistance survey this year using samples collected during 2015 and the GRDC-funded AHRI research is also focusing on shifts in weed phenology.

Portrait of Dr Michael Ashworth

Dr Michael Ashworth has been studying the adaptability of wild radish through a GRDC-funded Australian Herbicide Resistance Initiative project.

PHOTO: Cox Inall 

Using a field-collected population, researcher Dr Michael Ashworth recurrently selected wild radish over five generations for early flowering and over three generations for late flowering.

He then compared the flowering time and size characteristics of the initial weed population (unselected) to the early-flowering and late-flowering selected generations.

“When recurrently grown without flowering time selection, there was no tangible shift in time to reach 50 per cent of the population flowering 59 days after emergence,” he says.

“However, after five generations of early-flowering selection, the number of days to reach 50 per cent of the population flowering dropped to 29 days after emergence.

“Three generations of late flowering time selection also resulted in a significant shift, with flowering time doubling to 50 per cent of the population flowering 114 days after emergence.”

Dr Ashworth says such significant shifts in flowering time illustrate the adaptive capacity of wild radish and highlight the need to monitor weed populations for any changes as a result of new non-herbicide weed-control tactics.

“We need to think hard about how we use our current integrated weed management strategies and continually diversify the way we use them,” he says

Dr Ashworth suggests rotating the seeding order of paddocks, such as seeding the first paddocks last the following season, and using harvest weed-seed control strategies with highly competitive crops.

“It’s not all bad news, as earlier flowering wild radish plants will have lower seed production – that is, be less fit,” he says.

“This means if we stop favouring early-flowering individuals, there will be a rapid correction in flowering time back to what is optimal for that environment.

“Even diverse farming systems need diversity and it is always best to continually rotate your farming practices like you rotate your herbicides, while continually seeking to cater for change.”

More information:

Dr Michael Ashworth,
08 9266 5487,
m.ashworth@curtin.edu.au

Useful resources:

Integrated Weed Management Hub

Australian Herbicide Resistance Initiative

WeedSmart

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GRDC Project Code UWA00146

Region West