When it comes to growing canola, one of the key decisions is which herbicide system to use to set up paddocks for following rotations.
Triazine tolerant (TT), Roundup Ready® (RR) technology and the newer Roundup-Triazine (RT®) tolerant varieties all offer different integrated weed management tools to farmers to achieve the best outcome.
Synergy Consulting principal consultant David Pfeiffer said with the introduction of the dual herbicide tolerant Hyola 525RT and Hyola 725RT from Advanta Seeds, he was often asked ‘why move to RT?’
“The key reason for the adoption of RT is the combination of both knockdown and residual activity leading to increased weed control,” he said.
Mr Pfeiffer, who heads the independent network of agronomical businesses servicing Western Australia, Victoria and South Australia, said a canola herbicide systems trial at Mingenew last year comparing RT, RR and TT regimes demonstrated the efficacy of the herbicide system.
“In the trial, all three RT combination herbicide treatments achieved greater than 90 per cent control of ryegrass and wild radish.”
He said standalone Select® provided poor ryegrass control (10pc), highlighting the increase in clethodim resistant ryegrass and explaining the highly unacceptable ryegrass control for TT only system treatments.
Mr Pfeiffer said the TT system also provided inferior radish control relative to RT® due to the post-emergent knockdown application of glyphosate.
“Similarly, the RT canola treatments provided greater radish control relative to the RR treatment with the radish control a result of the extended residual activity from the atrazine.
“The improved residual weed control from the triazine could be seen with the control of later germinating grass and radish after the six-leaf-spray, which with the earlier time of sowing, typically happens before the end of May.
“This is especially the case in the “holes” void of crop that appear across most paddocks from either blocked rows or simply poorer than expected establishment.”
According to Mr Pfeiffer, the second and arguably most important reason for growing RT canola was resistance management.
“The combination of two modes of action reduces the likelihood of resistance developing to either triazine or glyphosate. This does however assume both are susceptible to start with.”
He said that was the message from University of Adelaide’s Dr Chris Preston to those who attended his IWM seminars across WA in September last year.
“He believes the use of different herbicide modes of action within one cropping season such as in the RT canola system is providing multiple opportunities to control weeds and minimise or delay the development of herbicide resistance.”
Mr Pfeiffer also touched on whether weed control was more important than yield in canola cropping.
“This answer will differ among growers.
“We all obviously opt for both; however, if we accept weed control is number one in many continuous cropping systems to ensure at least two ‘cleaner’ cereals following the canola rotation, we need to decrease weed numbers heading into the cereal phase, as there is already enough pressure on the pre-emergent chemistry in cereal crops.”