Bec and Ash Marshall, with Harry, plan to keep hay making in their rotation to stop weed seed set and to store soil moisture.
Increasing herbicide resistance in annual rye-grass has thrown up some challenges for Bec and Ash Marshall on their 3300ha farm at Normanville, south-west of Kerang, and led to a new approach to their farming system.
Hold tight - we’re checking permissions before loading more content
“Acknowledging that the solution to our rye-grass problem was not going to come in a drum was the first step in planning a long-term strategy to drive down weed numbers across our farming enterprise,” Bec said.
“Back in 2009, we were following a simple but profitable crop rotation of mostly cereals and a little vetch hay in a good year, herbicides were working well, and we had low grass weed numbers.
“We added lentils to the rotation in 2011, which gave us the option to use crop topping to target grass weed escapes.
“We were reasonably confident that we were doing enough to keep grass weeds under control with broader use of pre-emergent herbicides and opportunistic hay production.”
After a string of drier seasons, the Mallee’s wet start in 2017 signalled a significant turn of events for the Marshalls with their usual weed control program compromised, newly-purchased paddocks bringing with them higher grass weed numbers, and testing revealed that the rye-grass population was developing resistance to trifluralin, clethodim and glyphosate.
“It was clear that we needed to re-assess our farming system and develop a new long-term strategy for control,” Bec said.
“In 2018, we introduced oaten hay to the rotation, and although we have a love-hate relationship with hay, there is no doubt that it has made the biggest difference to the grass population in targeted paddocks.”
Hay has been profitable in its own right the past few years, but the Marshalls will keep it in their rotation just for the weed control effect and the risk management benefit of deep stored soil moisture.
They maintain that if a crop is ‘sown for hay, it’s cut for hay’, with no backing out at the end of the season.
The second tactic introduced in 2018 was to boost crop competition in their barley phase using higher seeding rates and to choose more competitive varieties such as Compass and, more recently, Leabrook, and in good years with sufficient stored moisture, Planet.
“Although it is hard to quantify the effect of increased crop competition on grass weeds, we can see the reduction in weeds in our more competitive barley varieties and know it is worthwhile,” Bec said.
The next tactic employed since 2018 is a more diverse pre-emergent herbicide program that includes mixing and rotating modes of action at every opportunity.
The main aim is to prolong the effective life of trifluralin, the most cost-effective pre-emergent herbicide option in their no-till farming system.
“Herbicide resistance testing is essential to planning an effective herbicide program for the farm,” Bec said.
“You have to know what still works and what will be ineffective to apply. The most expensive herbicide to apply is the one that doesn’t work.
“We use new products to increase diversity and herbicide mixes to minimise resistance. Trifluralin is rarely applied on its own these days unless paddocks are exceptionally clean.
“We find that pre-emergent herbicides provide a good return on investment in our system.
“In the oaten hay phase, we give the paddocks a complete break from pre-emergent herbicides.”
More recently, the Marshalls have needed to respond to escapes of glyphosate-resistant annual rye-grass from some fence-line areas into their crops.
They have introduced the double-knock for all glyphosate applications in crop and non-crop areas.
Bec said they were targeting small weeds with robust rates on their fence-lines, irrigation channels and check banks, as these were their most difficult areas for weed control.
In-crop, they apply glyphosate to terminate their hay crops before cutting and then apply paraquat after the hay is off.
In addition to these newer practices, the Marshalls continue to use narrow windrow burning for harvest weed seed control, albeit infrequently, crop topping all legumes, long grass break phases (three to five years) in their rotation and diversity of crops to vary the timing of planting and harvest operations, and herbicide modes of action.
Their crop rotation is now much more diverse and includes dryland wheat, barley, vetch (hay), oaten hay, lentils and canola, and faba beans on irrigation only.
“We have seen the benefits of resistance testing and implementing tactics that drive down weed numbers fast,” Bec said.
“We thought we were doing enough before, but it only took one year for the weed seed bank to really blow-out.
“We want to do everything we can to avoid that happening in the future, and stopping seed set is the key to keeping the seed bank numbers low across the farm.”
The WeedSmart Big 6 is an integrated weed management program that growers can apply across all cropping systems.
A diverse approach that includes several chemical and non-chemical tactics places downward pressure on the weed seed bank and reduces herbicide resistance risk.
For more information about implementing the WeedSmart Big 6, visit: www.weedsmart.org.au
– Contributed by Cindy Benjamin, WeedSmart
Bec Marshall says they are targeting small weeds with robust rates on their fence-lines, irrigation channels and check banks, as these are their most difficult areas for weed control.
The Marshalls use herbicide resistance testing to help plan an effective herbicide program for the farm. They are using new products to increase diversity and herbicide mixes to minimise resistance, while doing all they can to maintain efficacy in older chemistries.
