Australia
March 27, 2013
Adopting a zero weed seed set policy is a critical component of an integrated management strategy needed to combat wild radish, which has been declared a serious emerging issue in the southern cropping region.
Southern grain growers and their advisers have been told that thwarting herbicide-resistant wild radish – already a major established problem in the Western Australian wheat belt – requires a thorough understanding of the weed’s biological complexity and a concerted management effort.
Speaking at Grains Research and Development Corporation (GRDC) grains research Updates in the south, wild radish authority Bill Campbell has encouraged the southern cropping industry to learn from the WA experience.
Mr Campbell, of Nufarm Australia Ltd, based in WA, said growers and advisers could not afford to be apathetic about radish resistance and what is required to farm sustainably into the future.
He said that requirement involved the imperative adoption of a “multi mode of action, don’t tolerate any seed set” approach to all populations of wild radish.
“The big message to advisers and growers is manyfold – resistance testing, a thorough understanding of why and how radish has become problematic in any one paddock, and a through appreciation that the seed bank must be managed and a zero seed set policy adopted are all essential components to combating wild radish,” Mr Campbell said. “General farm hygiene is also an important component.”
Mr Campbell said that over the past 12 years in WA, where intensive cropping systems are more prevalent than in the south, herbicide resistance in wild radish had become more widespread and control notably more complex with the rapid loss of base chemistries.
“The unique biology of wild radish makes it a highly-adaptive, street-wise opponent.
“It is not only an out-crossing species proficient at sharing and spreading genetic change but has complex seed dormancy mechanisms that ensure subsequent germination during a season (and over a number of years), always preserving a portion of its gene pool from particular selective pressures within a crop and different crops over time. This biological complexity highlights the importance of seed bank management.”
Mr Campbell said that ultimately the erosion and running down of seed banks with a truly integrated weed management approach was the only way to eliminate some very special resistance genetics, “otherwise, the evolutionary process continues”.
Extensive Nufarm trials in WA have resulted in categorisation of wild radish population genetics into five defined stages of evolution or resistance development.
These five stages are: truly susceptible populations; partially susceptible populations; populations overtly resistant to individual mode of action (MOA) only; high level of MOA resistance with the first stages of stacked multiple resistance; and high levels of stacked multiple resistance, for which three-way MOA treatments with existing chemistry are not effective.
Stacked resistance is a form of multiple resistance where plants in a population independently develop resistance to herbicides with a different MOA and then eventually interbreed to produce individual plants resistant to more than one herbicide group.
Mr Campbell said it was possible to develop a paddock-specific strategy for controlling radish by knowing the resistance genetics present and the stage of resistance development and therefore the cost of treatment required.
“Best management practice is not to rely solely on new chemistries but to use mixtures of both old and new chemistry across populations to minimise selection pressure on all groups,” Mr Campbell said.
He said late spraying on larger plants in trying to limit operations to one spray only and utilising less than full label rates were among a number of fundamental errors that contributed to the promotion of resistance in WA.
GRDC-funded research across the western and southern regions is quantifying the extent of the wild radish problem and developing management systems to lower the weed’s on-farm seed bank.
To listen to the Radish Runs Wild episode of Driving Agronomy, in which Bill Campbell is interviewed, visit www.grdc.com.au/Driving-Agronomy or find the Driving Agronomy podcast on iTunes by searching for “GRDC”.
More information on herbicide resistance is available via www.weedsmart.org.au
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